Method for removing impurities and method for recovering metals

Abstract

Provided are a method for removing impurities that can effectively remove impurities from a lithium containing solution before electrodialysis, and a method for recovering metals. A method for removing impurities by removing at least a part of the impurities from a lithium containing solution that contains lithium ions and impurity metal ions derived from lithium ion battery waste, the method including: an impurity removal step of, before subjecting the lithium containing solution to electrodialysis, adding a pH adjusting agent comprising a lithium hydroxide solution to the lithium containing solution to increase a pH of the lithium containing solution, thereby depositing and separating the impurities.

Description

METHOD FOR REMOVING IMPURITIES AND METHOD FOR RECOVERING METALS

[0001] This specification discloses a method for removing impurities and a method for recovering metals.

[0002] In recent years, it has been widely studied for recovery of valuable metals from battery waste such as lithium ion battery waste discarded for expired product life, manufacturing defects or other reasons, in terms of effective utilization of resources.

[0003] To recover metals from lithium ion battery waste, for example, battery powder obtained through a heat treatment or the like is brought into contact with an acid leaching solution such as sulfuric acid, thereby leaching metals in the battery powder into an acid leaching solution. This provides a metal containing solution in which nickel, cobalt, manganese, aluminum, iron, and the like are dissolved.

[0004] Each metal is then separated from the metal containing solution. Specifically, as described in, for example, Patent Literatures 1 to 3, aluminum and iron which are impurities, as well as manganese, among the metals dissolved in the metal containing solution, are sequentially or simultaneously separated by neutralization or solvent extraction. Nickel and cobalt are then separated by solvent extraction and concentrated to remove them.

[0005] In such a process, for example, electrodialysis may be used so that a lithium containing solution such as an extracted solution is a lithium hydroxide solution or the like.

[0006] For example, Patent Literature 4 discloses: “a method for producing lithium hydroxide, comprising feeding an aqueous lithium carbonate solution or suspension to an anode tank in an electrolysis device comprising an anode tank, a cathode tank, and a cation exchange membrane to conduct electrolysis and generating a lithium hydroxide solution in the cathode tank through the cation exchange membrane”.

[0007] Also, Patent Literature 5 proposes: “a method for producing lithium hydroxide, comprising feeding an aqueous solution of lithium salts to a salt chamber to extract an acid from an acid chamber, and to extract an aqueous solution of lithium hydroxide from an alkali chamber using an electrodialysis device, wherein the electrolysis device comprises one or more sets of the acid chamber, the salt chamber, the alkali chamber and a water electrolysis chamber, wherein cation exchange membranes and anion exchange membranes are alternately provided between an anode and a cathode, wherein the one or more sets are arranged in the following order from the anode side to the cathode side: an anode chamber formed by the anode and the cation exchange membrane, the acid chamber defined by said cation exchange membrane and the anion membrane, the salt chamber defined by said anion exchange membrane and another cation exchange membrane, the alkali chamber defined by said anion exchange membrane and another cation exchange membrane, and the water electrolysis chamber defined by said anion exchange membrane and a new cation exchange membrane, and wherein the water electrolysis chamber made of the anion membrane on the most cathode side is defined by the cathode instead of the cation membrane".

[0008] [PTL 1] Japanese Patent Application Publication No. 2010-180439 A [PTL 2] U.S. Patent Application Publication No. 2011 / 0135547 A1 [PTL 3] Japanese Patent Application Publication No. 2014-162982 A [PTL 4] Japanese Patent Application Publication No. 2009-270188 A [PTL 5] Japanese Patent Application Publication No. 2011-31232 A

[0009] If the lithium containing solution to be used for electrodialysis as described above contains impurity metal ions other than lithium ions, the impurities may be deposited in the electrodialysis, resulting in short life time of the electrodialysis membrane or other problems. The impurities as used herein are referred to as impurities with the intention of distinguishing them from lithium ions that are the main components of the lithium containing solution used for electrodialysis, but they are also metals that can be recovered.

[0010] In order to suppress the occurrence of problems in electrodialysis due to the presence of impurity metal ions, it is considered that the lithium containing solution is brought into contact with a resin such as a chelating resin and a cation exchange resin, prior to electrodialysis, and the impurity metal ions in the lithium containing solution are removed by adsorbing them onto the resin.

[0011] However, when the impurities are removed by the resin, many types of chemicals are needed to regenerate the resin for reuse, as well as a large number of facilities are also needed accordingly. Therefore, alternative methods other than the use of the resin are desirable for removing impurity metal ions from the lithium containing solution.

[0012] This specification discloses a method for removing impurities that can effectively remove impurities from the lithium containing solution prior to electrodialysis, and a method for recovering metals.

[0013] Disclosed in this specification is a method for removing impurities by removing at least a part of impurities from a lithium containing solution that contains lithium ions and impurity metal ions derived from lithium ion battery waste, the method including an impurity removal step of, before subjecting the lithium containing solution to electrodialysis, adding a pH adjusting agent comprising a lithium hydroxide solution to the lithium containing solution to increase a pH of the lithium containing solution, thereby depositing and separating the impurities.

[0014] Also disclosed in this specification is a method for recovering metals by leaching the metals in battery powder derived from lithium ion battery waste, and separating and recovering the metals from a metal containing solution obtained by the leaching, the method including: returning a residue containing the impurities separated from the lithium containing solution in the impurity removal step of the method for removing impurities as described above back to at least one step of steps included in the leaching of the metals in the battery powder as well as the separation and recovery of the metals, and recovering at least a part of the impurities in the residue.

[0015] According to the method for removing impurities described above, the impurities can be effectively removed from the lithium containing solution before electrodialysis.

[0016] [Fig. 1] Fig. 1 is a flow chart illustrating an example of a metal recovery process including an impurity removal method according to an embodiment. [Fig. 2] Fig. 2 is a flow chart illustrating an example of a preprocessing step for obtaining battery powder from lithium ion battery waste. [Fig. 3] Fig. 3 is a cross-sectional view schematically illustrating an example of a bipolar membrane electrodialysis device that can be used in an electrodialysis step included in the metal removal method in Fig. 1. [Fig. 4] Fig. 4 is a graph illustrating a relationship between a pH and a ratio of each metal ion concentration obtained in a test for removing impurities from a lithium containing solution according to Test Example 1. [Fig. 5] Fig. 5 is a graph illustrating a relationship between a pH and a current efficiency of a lithium containing solution obtained in an electrodialysis test according to Test Example 2. [Fig. 6] Fig. 6 is a graph illustrating a relationship between a Li concentration of a lithium containing solution and a current efficiency obtained in an electrodialysis test according to Test Example 3.

[0017] Embodiments of the method for removing impurities and the method for recovering metals described above will be described below in detail. The method for removing impurities according to an embodiment includes an impurity removal method that is performed before subjecting a lithium containing solution that contains lithium ions and impurity metal ions to electrodialysis in order to remove at least a part of the impurities from the lithium containing solution. The lithium containing solution contains lithium ions and impurity metal ions derived from lithium ion battery waste.

[0018] In the above impurity removal step, a pH adjusting agent containing a lithium hydroxide solution is added to the lithium containing solution to increase a pH of the lithium containing solution. As a result, the impurity metal ions in the lithium containing solution are converted to compounds such as hydroxides, which are deposited and precipitated. The lithium ions in the lithium hydroxide solution contained in the pH adjusting agent are not substantially deposited and remain in the solution in the form of metal ions together with lithium ions contained in the lithium containing solution since before the impurity removal step. The impurities can be effectively removed from the lithium containing solution by separating the residue containing impurities deposited due to the increase in the pH by means of solid-liquid separation or the like.

[0019] The impurity removal method according to this embodiment may be incorporated into a metal recovery method including the respective steps illustrated in Fig. 1 as an example. In Fig. 1, the battery powder derived from lithium ion battery waste is subjected to an acid leaching step, a metal separation step, an impurity removal step, an electrodialysis step, and a crystallizing step in this order. The battery powder can be obtained by subjecting the lithium ion battery waste to the preprocessing step, as illustrated in Fig. 2. Here, the descriptions will be given with reference to Figs. 1 and 2, however Figs. 1 and 2 are merely examples and are not limited to such specific flows.

[0020] (Lithium Ion Battery Waste) The lithium ion battery waste of interest is lithium ion batteries which can be used in various electronic devices such as mobile phones and which have been discarded due to the expired life of the product, manufacturing defects or other reasons. The recovery of valuable metals from such lithium ion battery waste is preferred in terms of effective utilization of resources.

[0021] The lithium ion battery waste has housings containing aluminum and may contain, in the housings, cathode active materials composed of single metal oxide containing lithium and one selected from the group consisting of nickel, cobalt and manganese, or composite metal oxides containing lithium and two or more of those, or the like, and aluminum foils (cathode substrates) to which the cathode active materials are applied and fixed by, for example, polyvinylidene fluoride (PVDF) or other organic binders. In addition, the lithium ion battery waste may contain copper, iron, or the like. Further, the above housings may generally contain an electrolytic solution having an electrolyte such as lithium hexafluorophosphate dissolved in an organic solvent such as ethylene carbonate and diethyl carbonate.

[0022] (Preprocessing Step) In many cases, the lithium ion battery waste is subjected to a preprocessing step. The preprocessing step may include at least one of roasting, crushing and sieving. The lithium ion battery waste becomes battery powder through the preprocessing step. The roasting, crushing, and sieving in the preprocessing step may optionally be performed, respectively, or they may be performed in any order. The battery powder means a powder obtained by subjecting the lithium ion battery waste to any preprocessing to concentrate cathode material components. The battery powder may be obtained as a powder by crushing and sieving the lithium ion battery waste with or without a heat treatment to concentrate the cathode material components.

[0023] In the roasting, the above lithium ion battery waste is heated. The roasting decomposes and removes the electrolyte and organic binder, and can also convert metals such as lithium and cobalt contained in the lithium ion battery waste into a form that is easily soluble in the acid leaching solution during the acid leaching step. Although the roasting changes the composition of the cathode active material, the roasted material is also referred to as the cathode active material. During the roasting, the lithium ion battery waste is preferably heated, for example, maintained in a temperature range of 600°C to 800°C for 0.5 to 6 hours. The roasting can be carried out in either an air atmosphere or an inert atmosphere such as nitrogen, and the roasting in their atmospheres in that order or vice versa. As a roasting furnace, for example, a batch type stationary furnace or a continuous type rotary kiln furnace, or other various types of furnaces can be used.

[0024] After roasting, crushing can be performed. The crushing selectively separates the cathode active materials from the aluminum foils to which the cathode active materials are applied, while destroying the housings of the lithium ion battery waste. Various known apparatuses or devices can be used in the crushing. In particular, it is preferable to use an impact-type crusher that can crush lithium ion battery waste by applying an impact while cutting it. Examples of the impact-type crusher include a sample mill, a hammer mill, a pin mill, a wing mill, a tornado mill, and a hammer crusher.

[0025] After crushing the lithium ion battery waste, the sieving is performed by sieving it using a sieve having appropriate openings. Thus, aluminum or copper remains on the sieve, and the battery powder that has removed Al or Cu to some extent is obtained under the sieve. If the battery powder contains nickel, the nickel content is, for example, 1% by mass to 30% by mass, and typically 5% by mass to 20% by mass. If it contains cobalt, the cobalt content in the battery powder is, for example, 1% by mass to 30% by mass, typically 5% by mass to 20% by mass. The battery powder may also contain, for example, 2% to 8% by mass of lithium, 1% to 30% by mass of manganese, 1% to 10% by mass of aluminum, 1% to 5% by mass of iron, and 1% to 10% by mass of copper.

[0026] In order to extract substantially only lithium from the battery powder, the battery powder can be brought into contact with water prior to an acid leaching step as described below to leach the lithium in the battery powder into water. In this case, the battery powder as the water leached residue is subjected to the acid leaching step. However, the battery powder may be subjected to the acid leaching step without the water leaching. When the water leaching is not carried out, the lithium ion concentration in the liquid can be easily maintained at a higher level in wet processes after the acid leaching step.

[0027] (Acid Leaching Step) In the acid leaching step, the metals in the battery powder are brought into contact with an acid leaching solution containing a mineral or inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid to leach the metals. This dissolves the metals in the battery powder to provide a leached solution that contains those metals as metal ions. As used herein, the solution containing metals in the battery powder as metal ions is referred to as a metal containing solution. The metal containing solution includes the above leached solution obtained in the acid leaching step and sent to the next metal separation step, and a solution in the middle of the metal separation step.

[0028] For a pH, it may preferably be -0.5 to 3.0 in the acid leaching solution during leaching, and may be 0.5 to 2.0 in the leached solution after leaching is completed. During leaching, for example, the acidic leaching solution may be stirred at 100 rpm to 400 rpm using an agitator if necessary, and a temperature of the solution may be 50°C to 80°C, or further 65°C to 70°C.

[0029] Here, the residue containing impurities obtained in the impurity removal step described below is preferably returned back to the steps included in the leaching of the metals in the battery powder as well as the separation and recovery of the metals (the acid leaching step and the metal separation step in the example of Fig. 1), and especially returned back to the acid leaching step. As described in detail below, the residue after the impurity removal step can contain at least one selected from the group consisting of nickel, cobalt, manganese, and magnesium as a compound such as a hydroxide. By returning the residue back to the acid leaching step, for example, by mixing it with the battery powder to bring it into contact with the acid leaching solution together with the battery powder, or by adding the residue to the leached solution, not only the metals in the battery powder but also the metals as impurities in the residue can be separated and recovered in the metal separation step. This makes it possible to suppress metal loss.

[0030] The metal containing solution obtained in the acid leaching step may have a cobalt ion concentration of 10 g / L to 50 g / L, a nickel ion concentration of 10 g / L to 50 g / L, a manganese ion concentration of 0 g / L to 50 g / L, an aluminum ion concentration of 1.0 g / L to 20 g / L, an iron ion concentration of 0.1 g / L to 5.0 g / L, and a copper ion concentration of 0.005 g / L to 0.2 g / L. The concentrations of the metal ions in the solution can be confirmed by analysis using an ICP optical emission spectrometer.

[0031] (Metal Separation Step) In the metal separation step, each metal ion is separated from the metal containing solution obtained in the above acid leaching step. The metal separation step may include, for example, neutralization, manganese extraction, cobalt extraction, and nickel extraction in this order, as described below.

[0032] In neutralization, the pH of the metal containing solution is increased and the neutralized residue is separated to obtain a neutralized solution. The neutralization includes, for example, an aluminum removal stage of depositing and removing at least a part of the aluminum ions by increasing the pH of the metal containing solution, and, after that, an iron removal stage of adding an oxidizing agent to oxidize the iron ions, and optionally further increasing the pH, thereby depositing and removing iron ions. However, if the metal containing solution is substantially free of iron ions, the iron removal stage may be omitted. In each of the aluminum removal stage and the iron removal stage, the pH may be in the range of 3.0 to 4.5. In the iron removal stage, the ORP value during oxidation may be 300 mV to 900 mV. After aluminum is precipitated in the aluminum removal stage and iron is precipitated in the iron removal stage, each neutralization residue as the precipitates can be removed by solid-liquid separation such as filtration using known device and method such as filter presses and thickener.

[0033] In the aluminum removal stage and iron removal stage, as an alkaline pH adjusting agent, lithium hydroxide, sodium hydroxide, sodium carbonate, and ammonia can be used, for example. In particular, as the lithium hydroxide solution, the solution obtained in the electrodialysis step as described below can be used, and in this case, lithium ions are circulated in a series of step in the wet process. The oxidizing agent used in the iron removal stage is not particularly limited as long as it can oxidize iron, but it may preferably be manganese dioxide, a cathode active material, and / or a manganese-containing leached residue obtained by leaching a cathode active material.

[0034] For the metal containing solution as the neutralized solution, the remaining of manganese and possibly aluminum ions can also be extracted and removed by solvent extraction. In this case, the remaining of manganese and aluminum ions is extracted, resulting in a manganese extracted solution that have removed them.

[0035] In the manganese extraction, a phosphate ester-based extracting agent (di-2-ethylhexyl phosphate (abbreviated as D2EHPA or product name: DP-8R), and the like), or a mixture of the phosphate ester-based extracting agent and an oxime-based extracting agent made of aldoxime or mainly based on aldoxime (2-hydroxy-5-nonylacetophenone oxime (trade name: LIX 84), 5-dodecyl salicylaldoxime (trade name: LIX 860), a mixture of LIX 84 and LIX 860 (trade name: LIX984), 5-nonyl salicylaldoxime (trade name: ACORGAM 5640) and the like) can be used. During extraction, an equilibrium pH is preferably 2.3 to 3.5, and more preferably 2.5 to 3.0. The alkaline pH adjusting agent used herein may preferably be a lithium hydroxide solution obtained in an electrodialysis step as described below, but separately prepared sodium hydroxide or the like may also be used.

[0036] At the time of extraction, it is desirable to carry out extraction by countercurrent type multistage extraction in which directions of the flow of the aqueous phase and the solvent used for each extraction are opposite to each other. By doing so, the extraction of other metal ions such as cobalt ions, nickel ions, and lithium ions can be suppressed, and the extraction rate of manganese ions can be increased. In the case of the countercurrent type multistage extraction, it is effective to set the equilibrium pH at the first stage of extraction to a value in the above range, and decrease the equilibrium pH at the time of extraction through successive stages. The cobalt extraction and nickel extraction as described below are also desirable to carry out the countercurrent type multistage extraction.

[0037] Cobalt extraction can then be performed. In the cobalt extraction, cobalt ions are separated from the manganese extracted solution obtained after the manganese extraction by solvent extraction. In this case, the magnesium ions that may be contained in the metal containing solution may also be extracted and removed. In the cobalt extraction, it is preferable to use a solvent containing a phosphonate ester-based extracting agent such as 2-ethylhexyl phosphonate (trade name: PC-88A, Ionquest 801). During extraction, an equilibrium pH can preferably be 5.0 to 6.0, and more preferably 5.0 to 5.5. As the alkaline pH adjusting agent used herein, it is preferable to use a lithium hydroxide solution obtained in an electrodialysis step as described below, but separately prepared sodium hydroxide or the like may also be used.

[0038] The solvent that has extracted the cobalt ions can be scrubbed as necessary and then stripped with a stripping solution containing sulfuric acid, hydrochloric acid, or nitric acid, for example, at a pH of 2.0 to 4.0. The stripped solution can be then heated and concentrated to crystallize the cobalt ions as cobalt salts.

[0039] In nickel extraction, nickel ions are extracted in a solvent containing a carboxylic acid-based extracting agent such as neodecanoic acid and naphthenic acid in order to separate the nickel ions from the cobalt extracted solution after the extraction of the cobalt ions. In this case, an equilibrium pH is preferably 6.0 to 8.0, and more preferably 6.8 to 7.2. The pH adjusting agent used to adjust the pH may also be lithium hydroxide or the like, but a lithium hydroxide solution obtained in an electrodialysis step as described below is preferably used.

[0040] The cobalt extracted solution to be used for the nickel extraction preferably has a lower lithium ion concentration. This is because if the lithium ion concentration is higher, deposits containing lithium are generated during the extraction of nickel ions, so that smooth operation of extraction may be prevented. Specifically, the cobalt extracted solution often contains anions of inorganic acids such as sulfate ions. So, when the saturated solution of lithium salts made by the anions of inorganic acids and lithium ions contained in the cobalt extracted solution is a saturated lithium salt solution, the lithium ion concentration of the cobalt extracted solution during nickel ion extraction is preferably less than or equal to the lithium ion concentration of the saturated lithium salt solution. The saturated lithium salt solution as used herein means a saturated solution of lithium salts formed by major anions of inorganic acids (such as sulfate ions, nitrate ions or chloride ions) and lithium ions contained in the cobalt extracted solution. If the cobalt extracted solution contains the highest amount of sulfate ions among the anions of inorganic acids contained therein, then the above lithium salt is lithium sulfate.

[0041] Further, a pH adjusting agent containing lithium ions may be used to adjust the equilibrium pH during nickel ion extraction. In this case, the lithium ion concentration of the cobalt extracted solution during nickel ion extraction means the lithium ion concentration of the mixed solution of the cobalt extracted solution and the pH adjusting agent before the pH adjusting agent is used (before mixing), and the lithium ion concentration in the mixed solution is preferably less than or equal to the lithium ion concentration of the saturated lithium salt solution. The pH adjusting agent containing lithium ions includes, but not limited to, for example, lithium hydroxide. Lithium hydroxide may be in solid, such as powder, or in solution. The lithium hydroxide solution may be the lithium hydroxide solution obtained in the lithium recovery step as described below.

[0042] However, if the pH adjusting agent such as lithium hydroxide solution is used to adjust the equilibrium pH during nickel ion extraction, the lithium ion concentration locally increases at the point where the cobalt extracted solution is brought into contact with the pH adjusting agent, and the lithium ion concentration there exceeds the solubility, resulting in remarkable formation of precipitates containing lithium salts. The reason why the precipitates are deposited would be that the mixture of the cobalt extracted solution (aqueous phase) and the solvent (organic phase) is stirred in the nickel extraction step, so that the surfaces of the lithium salts will be covered by the solvent immediately after deposition, and as a result, the lithium salts are difficult to be dissolved in the aqueous phase and are deposited as precipitates. Therefore, when using the pH adjusting agent containing lithium ions, the sum of the value of the lithium ion concentration (g / L) of the cobalt extracted solution before the pH adjusting agent is used (before mixing) and the value of the lithium ion concentration (g / L) of the pH adjusting agent may be less than or equal to the value of the lithium ion concentration (g / L) of the saturated lithium salt solution. In other words, this means that when the value of the lithium ion concentration (g / L) of the cobalt extracted solution before the use of the pH adjusting agent (before mixing) is X, the value of the lithium ion concentration (g / L) of the pH adjusting agent is Y, and the value of the lithium ion concentration (g / L) of the saturated lithium salt solution is Z, the relationship of the equation: X + Y <= Z may be satisfied. For example, when the anions of the main inorganic acid in the cobalt extracted solution are sulfate ions, and the lithium ion concentration of the cobalt extracted solution before the pH adjusting agent is used (before mixing) is 10 g / L, the lithium ion concentration of the pH adjusting agent is 20 g / L, and the lithium ion concentration of the saturated lithium sulfate solution at a temperature of 40°C is 42.5 g / L, each value is substituted into the above equation to yield 10 + 20 = 30 <= 42.5, indicating that the above relationship is satisfied. Satisfying the above relationship effectively suppresses the local increase in the lithium ion concentration during mixing with the pH adjusting agent and the resulting generation of precipitates. In many cases, the solubility depends on the temperature. The above solubility is the solubility at the temperature at which extraction is performed.

[0043] In the extraction of nickel ions, the lithium ion concentration of the cobalt extracted solution is preferably adjusted so that the lithium ion concentration of the extracted solution separated from the solvent is less than 15 g / L.

[0044] The solvent that has extracted the manganese ions and / or the aluminum ions may be subjected to scrubbing as necessary, and subjected to stripping using a stripping solution containing sulfuric acid, hydrochloric acid, or nitric acid, for example, at a pH of 1.0 to 3.0. Thereafter, the stripped solution may be electrolyzed and dissolved as necessary, and then heated to concentrate it, so that the nickel ions can be crystallized as nickel salts such as nickel sulfate.

[0045] At least a part of the lithium containing solution after the nickel ions have been extracted can be mixed with the acid leaching solution and the mixture can be used in the acid leaching step. This allows the lithium ions contained in the lithium containing solution to be circulated in a series of steps including the acid leaching step and metal separation step. Preferably, after the lithium ion concentration of the lithium containing solution has been increased to some extent by thus circulating the lithium ions, an impurity removal step and an electrodialysis step as described below are carried out.

[0046] (Impurity Removal Step) The lithium containing solution after the metal separation step mainly contains lithium ions, but a trace amount of at least one metal ion selected from the group consisting of nickel ions, cobalt ions, manganese ions, and magnesium ions, typically nickel and / or magnesium ions, may also be contained. As used herein, such metals are referred to as impurities because they remain dissolved in the lithium containing solution other than lithium ions at this stage, but such impurities can be desirable to be recovered in view of the overall process of recovering metals from lithium ion battery waste.

[0047] In the impurity removal step, for example, a pH adjusting agent can be added to a lithium containing solution that may have a pH of 3.0 to 6.0 to increase the pH of the lithium containing solution, preferably to 8 to 13. When the pH is thus increased, the impurity metal ions of the lithium ions and impurity metal ions in the lithium containing solution can be selectively deposited and precipitated.

[0048] The pH adjusting agent should contain at least a lithium hydroxide solution and is preferably composed entirely of the lithium hydroxide solution. This is to prevent contamination of the other metals into the lithium containing solution when other metal salt solutions are used. The lithium ions in the pH adjusting agent maintains their metal ion form along with lithium ions in the lithium containing solution, and can also remain in the liquid after solid-liquid separation. Therefore, after the impurity removal step, the lithium ion concentration of the lithium containing solution increases.

[0049] As described above, even if the lithium ion concentration is lowered in nickel extraction to suppress the generation of deposits, the use of the pH adjusting agent containing the lithium hydroxide solution in the impurity removal step causes the lithium containing solution after the impurity removal step to have a higher lithium ion concentration with the addition of the lithium ions contained in the pH adjusting agent. In the electrodialysis step described below, the use of a lithium containing solution having a high lithium ion concentration may have advantages such as higher current efficiency. From this point of view, it is also preferable to use the pH adjusting agent containing the lithium hydroxide solution in the impurity removal step.

[0050] At least a part of the lithium hydroxide solution contained in the pH adjusting agent preferably employs a dialyzed solution obtained in the electrodialysis step as described later. In other words, it is suitable to use at least a part of the dialyzed solution as at least a part of the pH adjusting agent in the impurity removal step. This allows the lithium ions to circulate within a series of steps in the wet process and maintain the lithium ion concentration in the liquid at a higher level.

[0051] If the pH of the lithium containing solution, which is increased by adding the pH adjusting agent, is too low, the target impurity components may not be fully separated, and on the other hand, if the pH is too high, the lifetime of the membrane used in the subsequent electrodialysis step may be reduced. Therefore, the pH of the lithium containing solution after the pH adjusting agent is added is preferably from 8 to 13, and more preferably from 10 to 12.

[0052] The liquid temperature when increasing the pH of the lithium containing solution can be from 10°C to 70°C. At this time, the lithium containing solution may also be stirred for 10 to 30 minutes, for example. The higher the liquid temperature, the shorter the reaction time, but heating is not necessarily required.

[0053] After the impurities are sufficiently precipitated by increasing the pH of the lithium containing solution, the residue containing the impurities can be separated from the lithium containing solution by solid-liquid separation using a filter press, thickener or the like. Since the residue thus separated contains metals that were impurities, it is preferable to return the residue back to at least one step of the steps included in the leaching of the metals in the battery powder as well as the separation and recovery of metals in order to recover at least a part of the residue. The residue is particularly suitable to be returned to the acid leaching step as described above.

[0054] The lithium containing solution after the impurity removal step may, for example, have a lithium ion concentration of 10 g / L to 30 g / L, a nickel ion concentration of 1 mg / L or less, a magnesium ion concentration of 1 mg / L or less, a cobalt ion concentration of 1 mg / L or less, and a manganese ion concentration of 1 mg / L or less. The lithium containing solution used in the next step, the electrodialysis step, may preferably have a lithium ion concentration of 15 g / L or higher.

[0055] It should be noted that the impurities can also be removed by adsorption on resins such as chelating resins or cation exchange resins, but in this case, many chemicals and facilities are required to regenerate the resins after use. Since this embodiment removes the impurities by increasing the pH as described above, it does not require such a large number of chemicals and facilities, and is expected to be carried out at a relatively low cost as compared to the use of the resin.

[0056] (Electrodialysis Step) The lithium containing solution after the impurity removal step is a solution in which the impurities have been sufficiently removed. For such a lithium containing solution, electrodialysis can be satisfactorily performed in the electrodialysis step. In other words, when the lithium containing solution that contains a large amount of impure metal ions (especially divalent or higher metal ions) is used for electrodialysis, problems occur that the impurities are deposited during electrodialysis and the electrodialysis membrane (ion exchange membrane and the like) becomes unusable in a short period of time. In this embodiment, the impurity removal step is performed before the electrodialysis step, thereby reducing the occurrence of such problems in the electrodialysis step.

[0057] In the electrodialysis step, electrodialysis is performed, for example, using a commercially available bipolar membrane electrodialysis device, thereby creating a lithium hydroxide solution from a washed solution. As an example, a bipolar membrane electrodialysis device 1 (hereinafter, also referred to as an “electrodialysis device”) shown in Fig.3 has, in a cell, an anode 2 and a cathode 3; and a bipolar membrane 4, an anion exchange membrane 5, a cation exchange membrane 6, and a bipolar membrane 7, which are arranged in this order between the anode 2 and the cathode 3 from the anode 2 side to the cathode 3 side. These separate the interior of the cell into a desalination chamber R1 between the anion exchange membrane 5 and the cation exchange membrane 6, an acidic chamber R2 between the bipolar membrane 4 and the anion exchange membrane 5, and an alkaline chamber R3 between the cation exchange membrane 6 and the bipolar membrane 7. The bipolar membranes 4 and 7 are constructed by laminating a cation exchange layer and an anion exchange layer, respectively.

[0058] In order to carry out electrodialysis by the illustrated electrodialysis device 1, the washed solution is placed in the desalination chamber R1, and pure water is also placed in each of the acidic chamber R2 and the alkaline chamber R3, and a predetermined voltage is applied to the anode 2 and the cathode 3. Then, lithium ions (Li+) in the washed solution in the desalination chamber R1 pass through the cation exchange membrane 6 and move to the alkaline chamber R3. In the alkaline chamber R3, water (H2O) is decomposed by the bipolar membrane 7 and hydroxide ions (OH-) are present, so that a lithium hydroxide solution is obtained as a dialyzed solution.

[0059] On the other hand, the anions of the inorganic acid in the washed solution in the desalination chamber R1 pass through the anion exchange membrane 5 and move to the acidic chamber R2. In the acidic chamber R2, an acidic solution such as a sulfuric acid solution is generated by the anions and hydrogen ions (H+) generated from water (H2O) by the bipolar membrane 4. As a result, the dialyzed solution (lithium hydroxide solution) obtained in the alkaline chamber R3 contains substantially no anions of inorganic acid. It should be noted that the anions of the inorganic acid are sulfate ions (SO42-) in the illustrated example, but they may be nitrate ions (NO3-) or chloride ions (Cl-) depending on the type of the acid used in the acid leaching step.

[0060] In the desalination chamber R1, the lithium salt is separated from the washed solution as described above, and a desalinated solution remains. The anion concentration of the inorganic acid tends to be higher in the acidic solution than in the dialyzed solution (lithium hydroxide solution), and tends to be higher in the desalinated solution than in the dialyzed solution (lithium hydroxide solution).

[0061] The pH of the lithium containing solution to be used in the electrodialysis step may preferably be somewhat higher, such as 8 to 13, and even 10 to 12. The lithium ion concentration of the lithium containing solution to be used in the electrodialysis step may preferably be 15 g / L or higher, and even 25 g / L or higher. This is because the higher the pH, the higher the current efficiency of electrodialysis, as will be described in detail in Test Example 2 in the Example section. However, if the pH is too high, it may shorten the lifetime of the membrane incorporated into the electrodialysis device. Therefore, the pH of the lithium containing solution to be used in the electrodialysis step is preferably in the above range.

[0062] The dialyzed solution (lithium hydroxide solution) obtained by the electrodialysis as described above can be effectively used as a pH adjusting agent in the metal separation step. After the electrodialysis, the lithium hydroxide solution may optionally be used as a pH adjusting agent after increasing the lithium ion concentration of the lithium hydroxide solution by heat concentration or the like.

[0063] (Crystallizing Step) A part of the lithium hydroxide solution as the dialyzed solution obtained in the electrodialysis step can be subjected to a crystallizing step. For example, when the lithium hydroxide solution is returned back to the wet process as a pH adjusting agent as described above, the lithium in the battery powder newly added to the wet process may gradually increase the lithium ion concentration in the liquid. Depending on the lithium ion concentration, the crystallizing step may be performed to recover lithium hydroxide.

[0064] In the crystallizing step, a crystallizing operation such as heat concentration or vacuum distillation can be performed in order to deposit lithium hydroxide. For the heat concentration, a higher temperature during crystallizing leads to faster progression of the process, which is preferable. However, the temperature of the crystallized product after crystallizing can be a temperature of less than 60°C at which water of crystallization is not released. This is because anhydrous lithium hydroxide that has released the water of crystallization is deliquescent and thus difficult to be handled. The lithium hydroxide produced in the crystallizing step may be subjected to a pulverization process or the like in order to adjust it to required physical properties.

[0065] Next, tests related to the impurity removal method and the metal recovery method as described above were conducted, which will be described below. However, the descriptions herein are merely for illustrative and are not intended to be limited. In the following tests, an ICP emission spectrometer SPS3300 manufactured by Hitachi High-Tech Science Corporation was used for the measurement of the metal ion concentrations, and a multi-water quality meter MX-43X and a composite electrode GST -5841C manufactured by DKK-TOA CORPORATION was used for the measurement of the pH.

[0066] (Test Example 1) The battery powder was leached with sulfuric acid to obtain a metal containing solution, which was then subjected to neutralization, manganese extraction, cobalt extraction, and nickel extraction in this order to obtain a lithium containing solution having a Ni concentration of 0.012 g / L, a Mg concentration of 0.007 g / L, and a Li concentration of 15.5 g / L.

[0067] To the above lithium containing solution (test solution) was added a lithium hydroxide solution having a concentration of 28 g / L as a pH adjusting agent to increase the pH of the test solution to a predetermined value, and stirred and maintained for 20 to 30 minutes, and a test was then conducted for measuring the concentration of each metal ion in the treated solution. As a result, a graph illustrating the relationship between the pH and the ratio of the concentration of each metal ion in the treated solution to the concentration of each metal ion in the test solution was obtained, as illustrated in Fig. 4.

[0068] It is found from Fig. 4 that the ratio of Ni and Mg in the treated solution decreases as the pH of the lithium containing solution is increased, and nickel and manganese are deposited and precipitated accordingly. In particular, it is found that nickel is sufficiently removed at a pH of 10 or higher and manganese is sufficiently removed at a pH of 11.3 or higher. By returning the resulting residue, which is the precipitate, back to the steps included in the leaching of the metals in the battery powder as well as the separation and recovery of the metals, it is expected that the above nickel and manganese can be effectively recovered.

[0069] (Test Example 2) A test was conducted for subjecting each of a plurality of lithium containing solutions having a Li concentration of 15.5 g / L and different pH values to electrodialysis to prepare lithium hydroxide solutions (dialyzed solutions). The electrodialysis conditions were a constant voltage of 32 V and a liquid feed rate of 0.13 L / min / m2. To adjust the pH of the lithium containing solution, a lithium hydroxide solution having a concentration of 12 g / L was used.

[0070] A graph illustrating the relationship between the pH and the current efficiency obtained as a result of that test is shown in Fig. 5. The current efficiency was calculated by: (〈amount of lithium decreased in desalting solution (mol) × 96485 (C / mol)） / 〈amount of integrated current (A・s / cell) × number of cells〉%). The current efficiency was obtained by the same method for Test Example 3, described below.

[0071] It is found from Fig. 5 that as the pH of the lithium containing solution used for electrodialysis is higher, the current efficiency in electrodialysis is more improved. Therefore, increasing the pH of the lithium containing solution to remove the impurities in the lithium containing solution before electrodialysis would contribute to improving the current efficiency in electrodialysis.

[0072] (Test Example 3) A test was conducted for subjecting each of a plurality of lithium containing solutions having different Li concentrations in the range of 10 g / L to 20 g / L to electrodialysis to prepare lithium hydroxide solutions (dialyzed solutions). The electrodialysis conditions were a constant voltage of 32 V, and a feed rate of 0.13 L / min / m2.

[0073] A graph illustrating the relationship between the Li concentration (material liquid concentration) and the current efficiency obtained as a result of that test is shown in Fig. 6. It is found from Fig. 6 that as the Li concentration of the lithium containing solution used for electrodialysis is higher, the current efficiency in electrodialysis is more improved. Therefore, increasing the pH of the lithium containing solution using the lithium hydroxide solution and the Li concentration of the lithium containing solution to remove the impurities in the lithium containing solution before electrodialysis would contribute to improving the current efficiency in electrodialysis. Fig. 6 also illustrates the Li loss ratio, which is a value obtained by dividing the amount of Li in the dialyzed solution by the amount of Li in the lithium containing solution, and the Li loss ratios were equivalent regardless of the Li concentration of the lithium containing solution.

[0074] The above results suggest that the impurity removal method as described above may effectively remove the impurities from the lithium containing solution prior to electrodialysis.Description of Reference Numerals

[0075] 1. bipolar membrane electrodialysis device 2 anode 3 cathode 4, 7 bipolar membrane 5 anion exchange membrane 6 cation exchange membrane R1 desalination chamber R2 Acidic chamber R3 alkaline chamber

Claims

1. A method for removing impurities by removing at least a part of the impurities from a lithium containing solution that contains lithium ions and impurity metal ions derived from lithium ion battery waste, the method comprising: an impurity removal step of, before subjecting the lithium containing solution to electrodialysis, adding a pH adjusting agent comprising a lithium hydroxide solution to the lithium containing solution to increase a pH of the lithium containing solution, thereby depositing and separating the impurities.

2. The method for removing impurities according to claim 1, wherein the impurity metal ions comprise at least one selected from the group consisting of nickel ions, cobalt ions, manganese ions, and magnesium ions.

3. The method for removing impurities according to claim 1, wherein the pH of the lithium containing solution is increased to 8 to 13 in the impurity removal step.

4. A method for recovering metals by leaching the metals in battery powder derived from lithium ion battery waste, and separating and recovering the metals from a metal containing solution obtained by the leaching, the method comprising: returning a residue containing the impurities separated from the lithium containing solution in the impurity removal step of the method for removing impurities according to any one of claims 1 to 3 back to at least one step of steps included in the leaching of the metals in the battery powder as well as the separation and recovery of the metals, and recovering at least a part of the impurities in the residue.

5. The method for recovering metals according to claim 4, wherein the method further comprises an acid leaching step of bringing the metals in the battery powder into contact with an acid leaching solution to obtain the metal containing solution, and wherein the residue is returned back to the acid leaching step of the steps included in the leaching of the metals in the battery powder as well as the separation and recovery of the metals.

6. The method for recovering metals according to claim 4, wherein the method further comprises an electrodialysis step of subjecting the lithium containing solution after the impurity removal step to the electrodialysis using a bipolar membrane to obtain a dialyzed solution comprising a lithium hydroxide solution.

7. The method for recovering metals according to claim 6, wherein at least a part of the dialyzed solution is used as at least a part of the pH adjusting agent in the impurity removal step.

8. The method for recovering metals according to claim 6, wherein the impurity metal ions comprise nickel ions and / or magnesium ions, and wherein the lithium containing solution to be used for the electrodialysis step has a nickel ion concentration of 1 mg / L or less and a magnesium ion concentration of 1 mg / L or less.

9. The method for recovering metals according to claim 6, wherein the lithium containing solution to be used for the electrodialysis step has a pH of 8 to 13.

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