Method for recovering metal

Abstract

A method for recovering metal from lithium-ion battery waste includes: an acid leaching step for leaching metals in battery powder obtained from lithium-ion battery waste by an acid to obtain a metal-containing solution containing metal ions of cobalt ions and / or nickel ions; an extraction step for extracting one kind of metal ions from the metal-containing solution by solvent extraction to obtain a metal concentrated solution; a crystallization step for crystallizing the metal ions in the metal concentrated solution to obtain a metal salt and a crystallized liquid; a liquid circulation step for returning at least a part of the crystallized liquid to the extraction step and / or the crystallization step to be used; and a liquid removal step in which the metal concentrated solution after the extraction step contains sodium ions and part of the metal concentrated solution is withdrawn without being subjected to the crystallization step.

Description

Metal recovery method

[0001] This document describes a method for recovering metals from lithium-ion battery waste.

[0002] To recover valuable metals from lithium-ion battery waste, for example, the lithium-ion battery waste may be roasted or otherwise subjected to other predetermined dry pretreatments to obtain battery powder, which may then be subjected to wet treatment (see, for example, Patent Document 1).

[0003] 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 are dissolved. Next, aluminum ions and iron ions are removed from the metal-containing solution by neutralization if necessary, and then aluminum ions, manganese ions, cobalt ions, and nickel ions are separated from the metal-containing solution by solvent extraction. The metal-enriched solutions of the cobalt-containing solution and nickel-containing solution obtained by the solvent extraction of cobalt ions and nickel ions are sometimes subjected to crystallization treatment to extract metal salts such as cobalt salts and nickel salts. Lithium ions can then be recovered as lithium hydroxide or the like from the lithium-containing solution in which lithium ions remain.

[0004] International Publication No. 2018 / 181816

[0005] The post-crystallization solution obtained after extracting the metal salts in the above crystallization treatment may contain cobalt ions or nickel ions as metal ions. In order to suppress the loss of valuable metals such as cobalt and nickel, it is desirable to return the post-crystallization solution containing the above metal ions to the solvent extraction of cobalt ions or nickel ions, or to add it to the pre-crystallization solution and subject it to crystallization again.

[0006] On the other hand, the metal-containing solution contains sodium ions due to the sodium content of lithium-ion battery waste. For example, if the sodium ion concentration in the solution increases due to the circulation of lithium ions through a series of processes from neutralization to hydroxide, the sodium ion concentration in the metal-enriched solution after solvent extraction and the above-mentioned solution after crystallization also increases. This raises concerns about an increase in the sodium content in the metal salt.

[0007] This specification provides a metal recovery method that can effectively suppress an increase in sodium ion concentration in the liquid from solvent extraction to crystallization.

[0008] The metal recovery method described in this specification is a method for recovering metals from lithium-ion battery waste, and includes an acid leaching step in which metals in battery powder obtained from lithium-ion battery waste are leached with acid to obtain a metal-containing solution containing at least one metal ion selected from cobalt ions and nickel ions; an extraction step in which one of the metal ions is extracted from the metal-containing solution by solvent extraction to obtain a metal-enriched solution; a crystallization step in which the metal ions in the metal-enriched solution are crystallized to obtain a metal salt and a post-crystallization liquid; a liquid circulation step in which at least a portion of the post-crystallization liquid is returned to the extraction step and / or the crystallization step for use; and a liquid draining step in which the metal-enriched solution after the extraction step contains sodium ions and a portion of the metal-enriched solution is drained without being subjected to the crystallization step.

[0009] According to the above-described metal recovery method, an increase in the sodium ion concentration in the liquid during the period from solvent extraction to crystallization can be effectively suppressed.

[0010] 1 is a flow chart showing a metal recovery method according to an embodiment of the present invention, and FIG. 2 is a flow chart showing an example of a pretreatment process for obtaining battery powder from lithium ion battery waste, and FIG. 3 is a flow chart showing an example of a precursor production process and a positive electrode active material production process in which the metal-concentrated solution obtained by the metal recovery method of FIG.

[0011] The present invention will be described in detail below with reference to an embodiment thereof. The metal recovery method of one embodiment is a method for recovering metals from lithium-ion battery waste, and includes an acid leaching step, an extraction step, a crystallization step, a liquid circulation step, and a liquid removal step, as shown in FIG.

[0012] In the acid leaching process, metals in battery powder obtained from lithium-ion battery waste are leached with acid to obtain a metal-containing solution containing at least one metal ion selected from cobalt ions and nickel ions. In the extraction process (cobalt extraction process, nickel extraction process), one of the metal ions is extracted from the metal-containing solution by solvent extraction to obtain a metal-enriched solution (cobalt-containing solution, nickel-containing solution). In the crystallization process, the metal ions in the metal-enriched solution are crystallized to obtain metal salts (cobalt salt, nickel salt) and a crystallized solution. Because the crystallized solution contains cobalt ions and nickel ions, a liquid circulation process is performed to reduce their loss, as shown by the dashed line in Figure 1, and at least a portion of the crystallized solution is returned to the extraction process and / or crystallization process for reuse.

[0013] Here, for example, as described below, if lithium ions are circulated through a series of processes by, for example, subjecting the post-extraction solution (lithium-containing solution) after the nickel extraction process to a hydroxide process and returning the resulting lithium hydroxide solution or lithium hydroxide to a previous process, sodium ions originating from lithium-ion battery waste, etc., are concentrated in the solution of the series of processes. In this case, if the above-mentioned liquid circulation process is performed, the sodium ion concentration in the metal-enriched solution and the crystallization solution gradually increases due to the circulation of the solution from the extraction process to the crystallization process. To address this issue, in this embodiment, a liquid withdrawal process is performed in which a portion of the metal-enriched solution after the extraction process is withdrawn without being subjected to the crystallization process. This effectively suppresses the increase in sodium ion concentration in the solution from the extraction process to the crystallization process.

[0014] The extraction step, crystallization step, and liquid-removal step can be performed for at least one of the cobalt ions and the nickel ions. In the illustrated example, the extraction step, crystallization step, and liquid-removal step are performed for each of the cobalt ions and the nickel ions.

[0015] In more detail, the battery powder used in the flow of Fig. 1 may be obtained by subjecting lithium-ion battery waste to pretreatment processes such as roasting, crushing, and sieving, as exemplified in Fig. 2. Here, the details of each process will be described according to Figs. 1 to 3, but Figs. 1 to 3 are merely examples and are not limited to such specific flows.

[0016] (Lithium-ion battery waste) The lithium-ion battery waste in question is lithium-ion secondary batteries that can be used in mobile phones and various other electronic devices, and which have been discarded due to the end of the battery product's life, manufacturing defects, or other reasons. Recovering valuable metals from such lithium-ion battery waste is desirable from the perspective of effective resource utilization. Lithium-ion battery waste refers to lithium-ion batteries that are eligible for recycling, regardless of whether they are traded for a value, free of charge, or treated as industrial waste.

[0017] Lithium-ion battery waste has an aluminum-containing casing as an exterior that encases the battery. This casing can be made of aluminum alone, aluminum and iron, or aluminum laminate. Lithium-ion battery waste may also contain a cathode active material, such as a single metal oxide containing lithium and one or more selected from the group consisting of nickel, cobalt, and manganese, or a composite metal oxide containing two or more selected metals. The cathode active material may also be coated and fixed to an aluminum foil (cathode substrate) with an organic binder, such as polyvinylidene fluoride (PVDF). Lithium-ion battery waste may also contain copper, iron, etc. Furthermore, the casing of lithium-ion battery waste typically contains an electrolyte solution, such as lithium hexafluorophosphate, dissolved in an organic solvent. Examples of organic solvents that may be used include ethylene carbonate and diethyl carbonate.

[0018] (Pretreatment Process) In many cases, lithium-ion battery waste undergoes a pretreatment process as a dry process, but wet processing may also be included as part of the process. In the pretreatment process, at least one of roasting, crushing, and sieving may be performed. Lithium-ion battery waste undergoes the pretreatment process to become battery powder. The roasting, crushing, and sieving processes of the pretreatment process may be performed individually as needed, or may be performed in any order. Battery powder refers to powder obtained by separating and concentrating positive electrode material components from lithium-ion battery waste through some kind of pretreatment. Battery powder may also be obtained as a powder by concentrating positive electrode material components by crushing and sieving lithium-ion battery waste with or without heat treatment.

[0019] In the roasting process, the lithium-ion battery waste is heated. The roasting process can convert metals such as lithium and cobalt contained in the lithium-ion battery waste into a soluble form. The roasting process is preferably carried out by heating the lithium-ion battery waste, for example, at a temperature of 450°C to 1000°C, preferably 600°C to 800°C, for 0.5 to 4 hours. The roasting process can be carried out either in an air atmosphere or in an inert atmosphere such as nitrogen. Alternatively, both the air atmosphere and the inert atmosphere may be carried out in this order or in the reverse order. The roasting furnace may be either a batch furnace or a continuous furnace. For example, a stationary furnace may be used in the batch furnace, and a rotary kiln may be used in the continuous furnace. Various other furnaces may also be used.

[0020] During roasting, at least a portion of the electrolyte is removed from the lithium-ion battery waste by evaporation, etc. In many cases, when lithium-ion battery waste is heated during roasting, the components of the internal electrolyte evaporate sequentially, starting with those with low boiling points. When roasting is performed, the electrolyte is removed and rendered harmless, and the organic binder is decomposed, facilitating separation of the aluminum foil and the positive electrode active material during crushing and sieving, as described below. Note that although the composition of the positive electrode active material changes upon roasting, for convenience, the term "positive electrode active material" will be used herein even if the material has undergone roasting.

[0021] After roasting, the lithium-ion battery waste can be crushed to remove the positive electrode active material and other materials from the casings. In the crushing, the casings of the lithium-ion battery waste are destroyed and the positive electrode active material is selectively separated from the aluminum foil on which the positive electrode active material is applied.

[0022] For crushing, various known devices or equipment can be used, but it is particularly preferable to use an impact crusher that can crush lithium-ion battery waste by applying impact while cutting the waste. Examples of this impact crusher include a sample mill, hammer mill, pin mill, wing mill, tornado mill, and hammer crusher. A screen can be installed at the outlet of the crusher, and the lithium-ion battery waste is discharged from the crusher through the screen once it has been crushed to a size that can pass through the screen.

[0023] After crushing the lithium-ion battery waste, it is sieved using a sieve with appropriate openings, whereby aluminum and copper remain on the sieve and battery powder from which aluminum and copper have been removed to some extent is obtained below the sieve.

[0024] The battery powder obtained in the pretreatment step contains nickel, cobalt, lithium, manganese, etc. For example, but not limited to, the battery powder may contain 1% to 30% by mass of cobalt, 1% to 30% by mass of nickel, 2% to 8% by mass of lithium, and 1% to 30% by mass of manganese. The battery powder may further contain 1% to 10% by mass of aluminum, 1% to 5% by mass of iron, 1% to 10% by mass of copper, and 0.001% to 0.1% by mass of sodium.

[0025] (Acid Leaching Step) In the acid leaching step, an acidic leaching solution such as sulfuric acid is used to leach the metals in the battery powder. This results in a solution in which the metals in the battery powder are dissolved and a leaching residue that remains undissolved. Here, the solution in which the metals in the battery powder are dissolved is also referred to as a metal-containing solution in each step from the end of the acid leaching step to the nickel extraction step described below.

[0026] In the acid leaching step, the pH of the acidic leachate or post-leaching solution may be adjusted to less than 3.5. The oxidation-reduction potential (ORP value, based on silver / silver chloride potential) may be 100 mV or less. After leaching is completed, solid-liquid separation may be performed to separate the leaching residue from the metal-containing solution. However, the metal-containing solution containing the leaching residue may be subjected to the subsequent neutralization step without solid-liquid separation. As described below, the post-extraction solution from the nickel extraction step (a lithium-containing solution such as a lithium sulfate solution) or water may be used as a diluent for adjusting the pH of the acidic leachate. This allows lithium ions to circulate throughout the series of steps in the wet treatment, allowing the lithium ions in the solution to be concentrated during the process.

[0027] The metal-containing solution obtained in the acid leaching step may have, for example, a cobalt ion concentration of 5 g / L to 50 g / L, a nickel ion concentration of 10 g / L to 50 g / L, a lithium ion concentration of 2 g / L to 10 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, a copper ion concentration of 0.005 g / L to 0.2 g / L, and a sodium ion concentration of 0.001 g / L to 0.1 g / L.

[0028] (Neutralization Step) When the metal-containing solution obtained in the acid leaching step contains aluminum ions and / or iron ions, a neutralization step can be carried out after the acid leaching step. In the neutralization step, the pH of the metal-containing solution is increased, thereby precipitating aluminum ions and / or iron ions as solids, and the precipitate is separated. When the metal-containing solution contains aluminum ions and iron ions, the neutralization step preferably includes a dealumination step and a de-ironization step. However, when the metal-containing solution does not contain aluminum ions and / or iron ions, the dealumination step and / or the de-ironization step may be omitted.

[0029] In the dealumination step, the pH of the metal-containing solution is increased to precipitate at least a portion of the aluminum ions, which are then removed by solid-liquid separation. At this time, for example, by increasing the pH to within a range of 4.0 to 5.0 using a pH adjuster at a liquid temperature of 50 to 90° C., the aluminum ions can be effectively separated while suppressing the precipitation of nickel ions and / or cobalt ions.

[0030] In the iron removal step, an oxidizing agent is added, followed by a pH adjuster to raise the pH to a range of 4.0 to 5.0. This oxidizes the iron ions from divalent to trivalent, resulting in the deposition of solids such as iron oxide or iron hydroxide (Fe(OH)3), which can be removed by solid-liquid separation. The oxidation-reduction potential (ORP value, based on silver / silver chloride potential) during oxidation is preferably 300 mV to 900 mV. The oxidizing agent is not particularly limited as long as it can oxidize iron ions, but manganese dioxide, a positive electrode active material, and / or a manganese-containing leaching residue obtained by leaching the positive electrode active material are preferred. The manganese-containing leaching residue obtained by leaching the positive electrode active material with acid may contain manganese dioxide. When the above-mentioned positive electrode active material or the like is used as the oxidizing agent, a precipitation reaction occurs in which manganese ions in the solution become manganese dioxide, allowing the precipitated manganese to be removed along with the iron.

[0031] Examples of pH adjusters used in neutralization in the above-mentioned dealumination step, iron removal step, etc. include solid or liquid lithium hydroxide, sodium hydroxide, sodium carbonate, ammonia, etc., and among these, lithium hydroxide is preferred because it can prevent sodium and the like from being mixed into the lithium hydroxide produced in the hydroxide step described below. The lithium hydroxide solution or lithium hydroxide obtained in the hydroxide step described below can be used as the pH adjuster, thereby circulating lithium ions within the series of steps.

[0032] (Manganese Extraction Step) After the metal-containing solution has been subjected to the neutralization step as necessary, manganese ions can be extracted and removed by solvent extraction in the manganese extraction step. Here, if aluminum ions remain in the metal-containing solution, not only the manganese ions but also the aluminum ions are extracted and removed. However, the manganese extraction step may be omitted.

[0033] For the extraction of manganese ions, it is preferable to use an extractant containing a phosphate ester extractant. A specific example of a phosphate ester extractant is di-2-ethylhexyl phosphoric acid (abbreviation: D2EHPA, for example, trade name: DP8R). Alternatively, the extractant may be a mixture of a phosphate ester extractant and an oxime extractant. In this case, the oxime extractant is preferably an aldoxime or one containing aldoxime as the main component. Specific examples include 2-hydroxy-5-nonylacetophenone oxime (trade name: LIX84), 5-dodecylsalicyldoxime (trade name: LIX860), a mixture of LIX84 and LIX860 (trade name: LIX984), and 5-nonylsalicylaldoxime (trade name: ACORGAM5640).

[0034] The extractant may be diluted with a hydrocarbon organic solvent such as an aromatic, paraffinic, or naphthenic solvent to a concentration of 10% by volume to 30% by volume, and this may be used as the solvent.

[0035] During extraction, the equilibrium pH is preferably adjusted to 2.3 to 3.5, more preferably 2.5 to 3.0. The pH adjuster used at this time is preferably a lithium hydroxide solution, and for example, the lithium hydroxide solution obtained in the hydroxide step described below or lithium hydroxide can be used.

[0036] A mixer-settler may be used for extraction. In this case, the pH is first adjusted, for example, by adding a pH adjuster to the solvent. The metal-containing solution (aqueous phase) and the solvent (organic phase) are then mixed in the mixer to form a mixed solution, which is then stirred for, for example, 5 to 60 minutes. During this process, the target metal ions, such as manganese ions, in the metal-containing solution are transferred to the solvent. The temperature during extraction is set to room temperature (approximately 15 to 25°C) to 60°C or less, with 35 to 45°C being preferred for reasons of extraction speed, phase separation, and evaporation of the organic solvent. The mixed solution is then allowed to stand in the settler, and the aqueous and organic phases are separated based on the difference in their specific gravities. This results in a post-extraction solution from which the solvent has been separated. Extractions in processes other than the manganese extraction process can also be performed in a substantially similar manner.

[0037] During extraction, it is desirable to perform extraction by countercurrent multistage extraction, in which the aqueous phase and the solvent used in each extraction flow in opposite directions. This makes it possible to increase the extraction rate of manganese ions while suppressing the extraction of cobalt ions, nickel ions, and lithium ions. When using countercurrent multistage extraction, it is effective to set the equilibrium pH during the first extraction stage within the above-mentioned range and to lower the equilibrium pH during each subsequent extraction stage.

[0038] In the metal-containing solution after the manganese extraction step, for example, the cobalt ion concentration may be 0 g / L to 50 g / L, the nickel ion concentration may be 0 g / L to 50 g / L, the lithium ion concentration may be 1 g / L to 30 g / L, and the sodium ion concentration may be 0.001 g / L to 0.1 g / L.

[0039] (Cobalt Extraction Step) For example, if cobalt ions are contained in the metal-containing solution after the manganese extraction step, a cobalt extraction step can be carried out to extract and separate the cobalt ions from the metal-containing solution by solvent extraction.

[0040] For the extraction of cobalt ions, it is preferable to use a solvent containing a phosphoric acid extractant, especially a phosphonate extractant. 2-Ethylhexyl 2-ethylhexyl phosphonate (trade names: PC-88A, Ionquest 801) is particularly suitable from the viewpoint of the separation efficiency of nickel ions and cobalt ions. The extractant can be used as a solvent by diluting it with a hydrocarbon organic solvent to a concentration of 10% to 30% by volume.

[0041] When cobalt ions are extracted, the equilibrium pH during extraction is preferably 5.0 to 6.0, more preferably 5.0 to 5.5. If the pH is lower than 5.0, the cobalt ions may not be sufficiently extracted into the solvent. In this case, a lithium hydroxide solution is preferably used as the pH adjuster, and for example, the lithium hydroxide solution obtained in the hydroxide oxidation step described below or lithium hydroxide can be used.

[0042] When extracting cobalt ions, it is desirable to perform the extraction by countercurrent multistage extraction, in which the aqueous phase and the solvent flow in opposite directions in each extraction, which can increase the extraction rate of cobalt ions while suppressing the extraction of nickel ions and lithium ions.

[0043] During the extraction, not only cobalt ions but also small amounts of nickel ions and lithium ions may be extracted into the solvent. In this case, if necessary, the solvent from which the cobalt ions have been extracted may be subjected to one or more scrubbing steps using a scrubbing solution to remove nickel ions and lithium ions that may be contained in the solvent. The scrubbing solution may be, for example, a sulfuric acid solution with a pH of 3.5 to 5.5. The post-scrubbing solution may contain nickel ions and lithium ions. Therefore, it is desirable to mix some or all of the post-scrubbing solution with the metal-containing solution from the manganese extraction step and use this as the pre-extraction solution for the cobalt extraction step. This allows nickel ions and lithium ions to be circulated or retained within the series of steps and concentrated without loss. However, if the solvent from which the cobalt ions have been extracted does not contain nickel ions or lithium ions, scrubbing may not be necessary.

[0044] Thereafter, stripping is performed on a solvent containing cobalt ions. The stripping solution used for stripping may be any inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid, and can be appropriately selected depending on the subsequent mixing step and crystallization step. In many cases, sulfuric acid can be used as the stripping solution. Stripping is performed under pH conditions such that as much of the cobalt ions as possible are transferred from the solvent to the stripping solution. Specifically, the pH is preferably in the range of 2.0 to 4.0, and even more preferably in the range of 2.5 to 3.5.

[0045] (Nickel Extraction Step) When nickel ions are contained in the metal-containing solution after the cobalt ions have been extracted in the cobalt extraction step, a nickel extraction step can be carried out to extract nickel ions from the metal-containing solution by a solvent extraction method.

[0046] The solvent used in the nickel extraction step preferably contains a carboxylic acid extractant. Examples of carboxylic acid extractants include neodecanoic acid and naphthenic acid. Of these, neodecanoic acid (such as Versatic Acid 10 (VA-10) manufactured by Shell Chemical Industries, Ltd.) is preferred due to its ability to extract nickel ions. The extractant may be diluted with a hydrocarbon organic solvent such as an aromatic, paraffinic, or naphthenic solvent to a concentration of 10% by volume to 30% by volume, and this may be used as the solvent.

[0047] The equilibrium pH during extraction is preferably 6.0 to 8.0, more preferably 6.8 to 7.2. As a pH adjuster used to adjust the pH at this time, a lithium hydroxide solution is preferably used, and for example, the lithium hydroxide solution obtained in the hydroxide step described below or lithium hydroxide can be used.

[0048] The extraction is preferably performed in multiple stages using a countercurrent method, in which the metal-containing solution and the solvent flow in opposite directions. This suppresses the extraction of lithium ions into the solvent, thereby increasing the extraction rate of nickel ions. When performing multiple countercurrent extraction stages, it is effective to set the equilibrium pH during the first extraction stage within the above-mentioned range and then gradually lower the equilibrium pH during each stage.

[0049] If necessary, the solvent that has become nickel ion-containing after extraction may be subjected to one or more scrubbing steps using a scrubbing solution to remove lithium ions that may be contained in the solvent. The scrubbing solution may be, for example, a sulfuric acid acidic solution having a pH of 5.0 to 6.0. The post-scrubbing solution may contain lithium ions. Therefore, it is desirable to mix a portion or all of the post-scrubbing solution with the metal-containing solution obtained after the cobalt extraction step, and use this as the pre-extraction solution for the nickel extraction step. This allows the lithium ions to be circulated or retained within the series of steps and concentrated without loss. However, if the nickel ion-containing solvent does not contain lithium ions, scrubbing may not be necessary.

[0050] The stripping is then carried out using a solvent containing nickel ions. The stripping solution used for the stripping may be any inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid, and can be appropriately selected depending on the subsequent mixing and crystallization steps. In many cases, sulfuric acid can be used as the stripping solution. In the stripping, the pH is preferably in the range of 1.0 to 3.0, more preferably 1.5 to 2.5. The O / A ratio and the number of times can be appropriately selected, but the O / A ratio is 5 to 1, more preferably 4 to 2.

[0051] The post-extraction solution (lithium sulfate solution, etc.) after the nickel ions have been transferred to the solvent mainly contains lithium ions, and may be added to the acid leaching solution in the acid leaching step, thereby circulating the lithium ions contained in the post-extraction solution within the series of steps.

[0052] (Crystallization Step) The cobalt-containing solution and nickel-containing solution (metal-concentrated solution) obtained in the cobalt extraction step and nickel extraction step (extraction step) can be subjected to a crystallization treatment by a crystallization step.

[0053] In the cobalt crystallization step, the cobalt-containing solution (post-stripping solution) obtained by stripping in the cobalt extraction step described above is concentrated by heating, for example, to 40°C to 120°C. This causes cobalt ions to crystallize, yielding a cobalt salt such as cobalt sulfate. The cobalt salt thus obtained may have a nickel content of 5 ppm by mass or less.

[0054] In the nickel crystallization step, when a stripped solution such as a nickel sulfate solution is obtained by stripping, the nickel-containing solution obtained as the stripped solution obtained by stripping in the nickel extraction step described above, or the nickel-containing solution obtained by electrolyzing and dissolving the stripped solution as needed, is heated to 40° C. to 120° C. and concentrated, whereby nickel ions are crystallized to obtain a nickel salt such as nickel sulfate.

[0055] (Liquid Circulation Process) The liquid after crystallization in the cobalt crystallization process may contain cobalt ions and lithium ions that did not crystallize. It is desirable to mix such a liquid after crystallization with the cobalt-containing solution before the crystallization process and subject it to another crystallization process, or to use it in the cobalt extraction process to adjust the cobalt ion concentration of the scrubbing liquid used as the solvent for extracting cobalt ions, or to mix it with the metal-containing solution after the manganese extraction process and subject it to the cobalt extraction process. In this way, the cobalt ions and lithium ions can be circulated or retained within the series of processes and concentrated without loss.

[0056] Furthermore, the post-crystallization solution from the nickel crystallization step may contain nickel ions and lithium ions that have not crystallized. It is desirable to mix such post-crystallization solution with the nickel-containing solution before the crystallization step and subject it to another crystallization step, to use it to adjust the nickel ion concentration of the scrubbing solution for the solvent containing nickel ions, or to mix it with the metal-containing solution after the cobalt extraction step and subject it to the nickel extraction step. In this way, nickel ions and lithium ions can be circulated or retained within a series of steps and concentrated without loss.

[0057] It is sufficient that at least a portion of the post-crystallization liquid is returned to the extraction step and / or crystallization step, but it is not necessary to return the entire liquid.

[0058] As described above, when the crystallized liquid is returned to the previous step and circulated, the sodium concentration in the liquid may gradually increase. In this case, sodium may be mixed into the cobalt salt or nickel salt obtained in the crystallization step, degrading their quality.

[0059] In contrast, in this embodiment, a liquid-removal step is performed, and the metal-concentrated solution (cobalt-containing solution or nickel-containing solution) after the extraction step is removed without being subjected to the crystallization step. The remaining metal-concentrated solution after a portion of the metal-concentrated solution is removed in the liquid-removal step is subjected to the crystallization step. This removes some of the sodium in the metal-concentrated solution, thereby suppressing an increase in the sodium concentration.

[0060] The liquid-removal step may be carried out periodically or irregularly when the sodium ion concentration in the metal-enriched solution becomes high to a certain extent during the continuous operation of the extraction step and the crystallization step, or may be incorporated into these steps and carried out continuously. In any case, it is preferable to carry out the liquid-removal step so that the sodium ion concentration in the metal-enriched solution is maintained at 100 mg / L or less.

[0061] The metal-enriched solution extracted in the liquid-removal step contains sodium ions and is preferably used in a predetermined precursor production process described below. It is also possible to extract a portion of the solution after crystallization if the purpose is to remove sodium. However, it is preferable to extract the metal-enriched solution in the liquid-removal step described above, since it is no longer necessary to subject at least a portion of the metal-enriched solution to the crystallization step. Furthermore, by performing liquid-removal before the crystallization step, it is possible to suppress an increase in the sodium content in the metal salt compared to performing liquid-removal after the crystallization step.

[0062] To actually perform the liquid-removal process, a portion of the metal-concentrated solution can be removed from a container such as a storage tank used in a predetermined process as described above, or from a pipe or flow path used for transferring the solution between predetermined processes. More specifically, for example, a branch path can be provided in the pipe connecting the processes, and the flow rate of the metal-concentrated solution sent to the branch path and removed can be adjusted by a valve or the diameter of the pipe. However, the metal-concentrated solution can be removed by various specific methods, and such methods can be selected as appropriate.

[0063] (Hydroxylation step) The lithium-containing solution (post-extraction solution) such as the lithium sulfate solution after the nickel ions have been transferred to the solvent can be subjected to a hydroxylation step. The details of the hydroxylation step are not particularly limited as long as a lithium hydroxide solution can be prepared, but for example, a carbonation and chemical conversion method in which lithium carbonate is prepared and then calcium hydroxide is used, a chemical conversion method in which barium hydroxide is used, or a technique using electrodialysis can be employed.

[0064] When barium hydroxide is used, it is added to a lithium-containing solution, and a lithium hydroxide solution is obtained based on the reaction LiSO + Ba(OH) → 2LiOH + BaSO. Note that barium that may dissolve in the solution at this time can be separated and removed using a cation exchange resin, chelating resin, or the like.

[0065] In electrodialysis, a bipolar membrane electrodialysis device is used. A lithium-containing solution is placed in the deionization compartment between the anion exchange membrane and the cation exchange membrane. Pure water is placed in the acid compartment between the bipolar membrane and the anion exchange membrane and in the alkaline compartment between the cation exchange membrane and the bipolar membrane. A voltage is then applied between the electrodes. Lithium ions in the metal-containing solution in the deionization compartment migrate to the alkaline compartment, where the bipolar membrane decomposes the pure water into hydroxide ions, producing a lithium hydroxide solution. In addition, inorganic acid anions, such as sulfate ions, in the metal-containing solution in the deionization compartment pass through the anion exchange membrane and migrate to the acid compartment. Furthermore, in electrodialysis, most of the lithium salts are separated from the metal-containing solution in the deionization compartment, resulting in a deionized solution that is almost free of lithium salts.

[0066] At least a portion of the lithium hydroxide solution obtained as described above can be effectively used as an alkaline pH adjuster to be used in a series of steps, more specifically, in at least one step selected from the group consisting of a neutralization step, a manganese extraction step, a cobalt extraction step, and a nickel extraction step.

[0067] Alternatively, lithium hydroxide may be extracted from the lithium hydroxide solution by crystallization. For example, if the lithium hydroxide solution is returned to the process as a pH adjuster, the lithium ion concentration in the solution may gradually increase due to the lithium in the newly added battery powder. Crystallization can be performed according to the lithium ion concentration, and lithium ions can be extracted as lithium hydroxide.

[0068] In crystallization, a crystallization procedure such as heat concentration or vacuum distillation can be performed to precipitate lithium hydroxide. In the case of heat concentration, a higher temperature during crystallization is preferable because the process proceeds more quickly. However, after crystallization, the temperature during drying of the crystallized product is preferably less than 60°C, at which water of crystallization does not desorb. This is because anhydrous lithium hydroxide from which water of crystallization has been desorbed is deliquescent and therefore difficult to handle. Thereafter, a pulverization process or the like can be performed to adjust the lithium hydroxide to the required physical properties.

[0069] (Precursor and Cathode Active Material Manufacturing Process) To manufacture a precursor of a lithium ion battery cathode active material (also simply referred to as "cathode active material"), for example, a mixing step, a coprecipitation step, and a washing step can be carried out in sequence, as shown in Fig. 3. To further manufacture the cathode active material, the precursor can be subjected to a calcination step.

[0070] In the mixing step, the metal-enriched solution (cobalt-containing solution and / or nickel-containing solution) is used to prepare a mixed solution such as a sulfuric acid solution containing cobalt ions, nickel ions, and manganese ions. Specifically, the cobalt ions, nickel ions, and manganese ions can be mixed in a solution containing the cobalt-containing solution and / or nickel-containing solution while adding a manganese source, a cobalt source, a nickel source, or the like as needed. The amounts of the cobalt-containing solution and / or nickel-containing solution and the manganese source, etc., added can be determined depending on the desired composition of the precursor or positive electrode active material to be produced, etc.

[0071] As described above, the cobalt-containing solution and / or the nickel-containing solution contain sodium ions. These sodium ions are brought into the mixed solution during the mixing step, and therefore the mixed solution contains sodium ions.

[0072] In the coprecipitation step, a pH adjuster is added to the mixed solution to adjust the pH, and a complexing agent is added. This causes a coprecipitation reaction, resulting in the precipitation of cobalt ions, nickel ions, and manganese ions in the mixed solution, resulting in a composite salt containing cobalt, nickel, and manganese. Typically, this composite salt may be a composite hydroxide containing cobalt, nickel, and manganese. The coprecipitation reaction can be carried out under conditions commonly employed in the production of precursors for positive electrode active materials.

[0073] Here, sodium hydroxide is used as the pH adjuster. As a result, impurities introduced due to the use of the pH adjuster become the same sodium impurities introduced from the cobalt-containing solution and / or nickel-containing solution and contained in the mixed solution as described above. This sodium is then mixed into the composite salt produced by the coprecipitation reaction, but can be effectively removed by the washing step described below. If a pH adjuster other than sodium hydroxide is used, the addition of such a pH adjuster will result in the introduction of impurities other than sodium into the composite salt, and even if the sodium is removed, these impurities may remain in the precursor.

[0074] The composite salt obtained in the co-precipitation step is washed in the washing step to become a precursor. This washing is mainly performed for the purpose of removing impurities such as sodium contained in the composite salt. The composite salt produced in the co-precipitation step tends to have sodium attached mainly to its particle surface. Therefore, if the composite salt is washed in the washing step, the sodium attached to the particle surface is washed away, and a precursor with a sufficiently low sodium content is obtained.

[0075] In the washing, for example, the composite salt is put into a washing liquid such as pure water to form a slurry, and after performing an operation such as stirring as necessary, the composite salt can be extracted by solid-liquid separation. Such washing is not limited to being performed only once, and may be repeated multiple times.

[0076] The post-washing solution obtained after washing may contain small amounts of cobalt ions and nickel ions in addition to sodium ions. If this post-washing solution is returned to the above-mentioned metal recovery method, a small amount of cobalt and nickel can be recovered, but a significant amount of sodium will be introduced. Therefore, it is preferable to discard the post-washing solution and not return it to the metal recovery method.

[0077] To produce a positive electrode active material, the precursor is subjected to a calcination process. In the calcination process, the precursor obtained in the coprecipitation process described above is mixed with a lithium source by kneading or the like, and the mixture is heated and calcined. Here, the lithium hydroxide obtained in the hydroxide process described above may be used as the lithium salt. After the calcination process, crushing or other treatments may be performed as necessary, for example, to obtain Li[Ni a Co b Mn (1-a-b) ]O2(NCM) or Li[Ni a Co b Al (1-a-b) ] (NCA) ternary system, or Li[Ni a Co b Mn c Al (1-a-b-c) ] (NCMA) or other positive electrode active materials can be produced.

Claims

1. A method for recovering metals from lithium ion battery waste, comprising: an acid leaching step of leaching metals in battery powder obtained from lithium ion battery waste with acid to obtain a metal-containing solution containing at least one type of metal ion selected from cobalt ions and nickel ions; an extraction step of extracting one type of metal ion from the metal-containing solution by solvent extraction to obtain a metal-enriched solution; a crystallization step of crystallizing the metal ions in the metal-enriched solution to obtain a metal salt and a crystallized liquid; a liquid circulation step of returning at least a portion of the crystallized liquid to the extraction step and / or the crystallization step for use; and a liquid draining step in which the metal-enriched solution after the extraction step contains sodium ions and a portion of the metal-enriched solution is drained without being subjected to the crystallization step.

2. The metal recovery method according to claim 1, wherein the metal-enriched solution extracted in the liquid-removal step is used in a precursor production process for a lithium-ion battery positive electrode active material, and the precursor production process includes using sodium hydroxide as a pH adjuster to generate a composite salt containing cobalt, nickel and manganese by a coprecipitation reaction.

3. A metal recovery method according to claim 1 or 2, further comprising a hydroxide step of producing a lithium hydroxide solution from the lithium-containing solution obtained after the extraction step, and / or producing lithium hydroxide by crystallization using the lithium hydroxide solution.

4. The metal recovery method according to claim 3, wherein the lithium hydroxide solution and / or lithium hydroxide is used as a pH adjuster in the extraction step.

5. A metal recovery method as described in claim 3, wherein the metal-containing solution contains aluminum ions and / or iron ions, and a neutralization step is included between the acid leaching step and the extraction step, in which the pH of the metal-containing solution is increased to precipitate aluminum ions and / or iron ions, and the lithium hydroxide solution and / or lithium hydroxide is used as a pH adjuster in the neutralization step.

6. The metal recovery method according to claim 3, wherein the lithium hydroxide is produced in the hydroxide oxidation step, and the lithium hydroxide is used in a process for producing a positive electrode active material.

7. A metal recovery method according to claim 1 or 2, wherein the lithium-containing solution obtained after the extraction step is used in the acid leaching step.

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