Metal recovery method

Abstract

Provided is a metal recovery method capable of contributing to cost reduction and the suppression of metal loss. The present invention relates to a method for recovering metals from lithium-ion battery waste, the method comprising: a cobalt extraction step including performing extraction of cobalt ions into a solvent and stripping of cobalt ions from the solvent, in this order with respect to a metal-containing solution, which contains cobalt ions, obtained by leaching metals from battery powder of lithium-ion battery waste; and a cobalt re-extraction step including performing extraction of cobalt ions into a solvent, scrubbing of the solvent, and stripping of cobalt ions from the solvent, in this order with respect to a post-stripping solution obtained in the cobalt extraction step. In the cobalt extraction step, a pH adjusting agent containing lithium hydroxide is used. In the cobalt re-extraction step, a pH adjusting agent containing at least one among sodium hydroxide and potassium hydroxide is used. At least a portion of a post-scrubbing solution, which contains cobalt ions and sodium ions, obtained by the scrubbing in the cobalt re-extraction step is subjected to the extraction in the cobalt re-extraction step together with the post-stripping solution obtained in the cobalt extraction step.

Description

Metal recovery method

[0001] This specification describes a metal recovery method.

[0002] In recent years, recovering valuable metals from battery waste such as lithium-ion battery waste discarded due to product end-of-life, manufacturing defects or other reasons has been widely studied from the perspective of effective utilization of resources.

[0003] To recover valuable metals from lithium-ion battery waste, battery powder obtained by subjecting lithium-ion battery waste to heat treatment or other predetermined dry pretreatment is often subjected to wet processing.

[0004] In wet processing, for example, metals such as cobalt, nickel, manganese, lithium, aluminum, and iron contained in battery powder are leached with an acid to obtain a metal-containing solution in which the metals are dissolved. Next, aluminum, iron, manganese, etc. are removed, and cobalt and nickel are separated from the metal-containing solution by pH adjustment or solvent extraction. Technologies related to this include those described in patent documents, for example.

[0005] Patent Document 1 discloses "a method for efficiently recovering metals from lithium-ion battery waste while suppressing the use of sodium hydroxide as a pH adjuster", and describes "a method for recovering metals from lithium-ion battery waste, the method comprising wet processing in which metals including lithium in lithium-ion battery waste are leached with an acid, and the metals are extracted from the metal-containing solution in which the metals are dissolved, wherein the lithium extracted in the wet processing is used as a pH adjuster to be used in the wet processing", and further recites that "the lithium is extracted as an aqueous lithium hydroxide solution in the wet processing, and the aqueous lithium hydroxide solution is used as the pH adjuster".

[0006] Patent Document 2 proposes a method for producing a cobalt solution, which aims to "effectively remove magnesium ions from a cobalt-containing solution containing magnesium ions," and includes a magnesium separation step in which, after extracting cobalt ions from the cobalt-containing solution using a solvent containing a carboxylic acid extractant to separate magnesium ions, the cobalt ions are back-extracted from the solvent to obtain the cobalt solution as a back-extracted liquid. The method includes "a cobalt extraction step in which, from a metal-containing solution containing cobalt ions, nickel ions, and magnesium ions, a portion of the cobalt ions and magnesium ions are extracted using a solvent containing a phosphonic acid ester extractant, and at least the cobalt ions are back-extracted from the solvent to obtain the cobalt-containing solution."

[0007] Japanese Patent Publication No. 2023-100242, International Publication No. 2023 / 079834

[0008] The technologies described in Patent Documents 1 and 2 have room for improvement from the standpoint of further reducing costs and suppressing metal loss by reviewing the chemicals used in the predetermined process and the return destination of the solution generated after the predetermined process.

[0009] This specification provides a metal recovery method that can contribute to cost reduction and suppression of metal loss.

[0010] The metal recovery method disclosed in this specification is a method for recovering metal from lithium-ion battery waste, comprising: a cobalt extraction step, which includes extracting cobalt ions into a solvent and back-extracting cobalt ions from the solvent in this order, with respect to a metal-containing solution obtained by leaching metal from the battery powder of lithium-ion battery waste and containing cobalt ions; and a cobalt re-extraction step, which includes extracting cobalt ions into a solvent, scrubbing the solvent, and back-extracting cobalt ions from the solvent in this order, with respect to the back-extracted solution obtained in the cobalt extraction step, wherein a pH adjusting agent containing lithium hydroxide is used in the cobalt extraction step, a pH adjusting agent containing at least one of sodium hydroxide and potassium hydroxide is used in the cobalt re-extraction step, and at least a portion of the scrubbing solution obtained in the scrubbing of the cobalt re-extraction step and containing cobalt ions and sodium ions is subjected to the extraction in the cobalt re-extraction step together with the back-extracted solution obtained in the cobalt extraction step.

[0011] The metal recovery method described above can contribute to cost reduction and suppression of metal loss.

[0012] This is a flowchart illustrating a metal recovery method according to one embodiment. This is a flowchart illustrating an example of pretreatment for obtaining battery powder from lithium-ion battery waste. This is a flowchart illustrating the details of the process from obtaining a cobalt salt from a metal-containing solution.

[0013] The embodiments of the metal recovery method described above will be explained in detail below. One embodiment of the metal recovery method is a method for recovering metal from lithium-ion battery waste, and this method includes at least a cobalt extraction step and a cobalt re-extraction step.

[0014] The cobalt extraction process involves extracting cobalt ions into a solvent and then back-extracting cobalt ions from the solvent, in that order, from a metal-containing solution obtained by leaching metal from the battery powder of lithium-ion battery waste. The cobalt re-extraction process involves extracting cobalt ions into a solvent, scrubbing the solvent, and then back-extracting cobalt ions from the solvent, in that order, from the back-extracted solution obtained in the cobalt extraction process.

[0015] In the cobalt extraction process, a pH adjuster containing lithium hydroxide is used. Lithium can often be present as one of the metal ions in metal-containing solutions. Therefore, even if lithium ions are introduced into the post-extraction solution from the cobalt extraction process due to the use of the above pH adjuster, this lithium can be recovered, for example, in a subsequent hydroxide step after the nickel extraction process, and does not adversely affect the wet processing.

[0016] On the other hand, the cobalt re-extraction process uses a pH adjuster containing at least one of sodium hydroxide and potassium hydroxide. If lithium hydroxide is used as the pH adjuster in the cobalt re-extraction process, the post-extraction solution may contain lithium ions derived from that lithium hydroxide. The post-extraction solution generated in the cobalt re-extraction process is sometimes discarded, which results in a loss of lithium. Alternatively, to avoid this loss of lithium, if the post-extraction solution from the cobalt re-extraction process is mixed with the post-extraction solution from the nickel extraction process and the lithium is recovered in the hydroxide process, it becomes necessary to remove the magnesium ions that are distributed into the post-extraction solution in the cobalt re-extraction process to separate magnesium ions before the hydroxide process, which increases costs. Moreover, in this case, the lithium ions contained in the post-extraction solution will only be those derived from the pH adjuster used in the cobalt re-extraction process, and the amount recovered will be small. Therefore, recovering lithium by removing magnesium ions before the hydroxide process is undesirable from a cost-effectiveness standpoint. Furthermore, the post-extraction solution from the cobalt re-extraction process often has a lower lithium ion concentration than the post-extraction solution from the nickel extraction process. Mixing these solutions reduces the efficiency of electrodialysis and other processes in the hydroxide process. To avoid or suppress such lithium loss and increased costs, in this embodiment, the pH adjusting agent used in the cobalt re-extraction process contains at least one of sodium hydroxide and potassium hydroxide. In the cobalt re-extraction process, a pH adjusting agent containing sodium hydroxide may be used.

[0017] For example, when a pH adjuster containing sodium hydroxide is used in the cobalt re-extraction process, sodium ions that may migrate to the solvent after extraction along with cobalt ions can be removed by scrubbing the solvent after extraction. Furthermore, the scrubbed solution obtained by this scrubbing may contain not only sodium ions but also cobalt ions. By subjecting at least a portion of this solution to the cobalt re-extraction process together with the back-extracted solution from the cobalt extraction process, cobalt loss can be suppressed. However, if the scrubbed solution is used for extraction in the cobalt extraction process instead of the cobalt re-extraction process, even if cobalt loss is suppressed, sodium ions will be mixed into the extracted solution and become impurities.

[0018] The metal recovery method described above may include, as shown in Figure 1 as an example, an acid leaching step, a pH raising step, a manganese extraction step, a cobalt extraction step, a nickel extraction step, a hydroxide step, and a crystallization step in this order. Battery powder can be obtained by performing a pretreatment process as shown in Figure 2 on lithium-ion battery waste. The metal recovery method according to Figures 1 and 2 will be described in detail below, but Figures 1 and 2 are illustrative and not limited to such specific flows.

[0019] (Lithium-ion battery waste) The lithium-ion battery waste covered by this analysis consists of lithium-ion secondary batteries that can be used in mobile phones and other various electronic devices, and which have been discarded due to the battery product's lifespan, manufacturing defects, or other reasons. Recovering valuable metals from such lithium-ion battery waste is desirable from the standpoint of effective resource utilization.

[0020] Lithium-ion battery waste may have an aluminum-containing casing, and within that casing may be a positive electrode active material consisting of lithium and a single metal oxide or a composite metal oxide containing two or more of these metals, or an aluminum foil (positive electrode substrate) on which the positive electrode active material is coated and fixed with, for example, polyvinylidene fluoride (PVDF) or other organic binders.

[0021] Furthermore, lithium-ion battery waste may contain copper, iron, etc., in components such as the negative electrode and casing. In addition, the casing may contain an electrolyte solution in which an electrolyte such as lithium hexafluoride phosphate is dissolved in an organic solvent such as ethylene carbonate or diethyl carbonate.

[0022] (Pre-treatment process) In most cases, lithium-ion battery waste undergoes a pre-treatment process for dry processing. Lithium-ion battery waste becomes battery powder through the pre-treatment process. The pre-treatment process may include at least one of the following: heat treatment, crushing, and physical separation. The heat treatment, crushing, and physical separation in the pre-treatment process may be performed individually as needed, and may be performed in any order. Battery powder refers to powder obtained by separating and concentrating the positive electrode material components through some kind of pre-treatment of lithium-ion battery waste. Battery powder can also be obtained as a powder by concentrating the positive electrode material components by crushing and physical separation of lithium-ion battery waste, with or without heat treatment.

[0023] In the heat treatment, the lithium-ion battery waste described above is heated. Heat treatment decomposes and removes the electrolyte and organic binder, and metals such as lithium and cobalt contained in the lithium-ion battery waste can be transformed into a form that is easily soluble in the acidic leaching solution during the acid leaching process. Although the composition of the positive electrode active material changes due to heat treatment, it is still referred to as positive electrode active material in this context. During heat treatment, the lithium-ion battery waste is heated and maintained at a temperature range of, for example, 100°C to 800°C for 0.5 to 6 hours. The heat treatment can be performed in an atmospheric environment or an inert atmosphere such as nitrogen, and the heat treatment may be carried out in either this order or the reverse order. As the heat treatment furnace, for example, a batch-type stationary furnace or a continuous-type rotary kiln furnace or various other types of furnaces can be used.

[0024] In crushing, the casing of the lithium-ion battery waste is destroyed, and the positive electrode active material is selectively separated from the aluminum foil coated with the positive electrode active material. Various known devices or equipment can be used for crushing, but it is particularly preferable to use an impact-type crusher that can crush the lithium-ion battery waste by applying impact while cutting it. Examples of such impact-type crushers include sample mills, hammer mills, pin mills, wing mills, tornado mills, and hammer crushers.

[0025] After crushing lithium-ion battery waste, physical separation can be performed, such as sieving using a sieve with an appropriate mesh size. This results in battery powder where aluminum and copper remain on the sieve and aluminum and copper have been removed to some extent below the sieve. Other physical separation methods may be performed in conjunction with or instead of sieving. By appropriately setting the conditions of the physical separation screen, the aluminum content in the battery powder can be adjusted.

[0026] Furthermore, in order to extract essentially only lithium from the battery powder, the battery powder may be brought into contact with water before the acid leaching process described later, allowing the lithium in the battery powder to leach into the water. In this case, the acid leaching process is performed on the battery powder remaining as a residue after the water leaching. However, the battery powder may also be subjected to the acid leaching process without water leaching. If water leaching is not performed, it becomes easier to maintain a high lithium ion concentration in the liquid during the wet processing after the acid leaching process.

[0027] The battery powder obtained in the pretreatment step, if it contains nickel, has a nickel content of, for example, 1% to 30% by mass, typically 5% to 20% by mass. If it contains cobalt, the cobalt content in the battery powder is, for example, 1% to 30% by mass, typically 5% 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, 1% to 10% by mass of copper, and 1% to 10% by mass of fluorine. The content of elements other than fluorine in the battery powder is determined by dissolving the battery powder in acid and quantifying the dissolved components using an ICP emission spectrometer. The fluorine content is measured by heating the battery powder and measuring it by ion chromatography. Such battery powder is subjected to a wet treatment including the acid leaching step described below.

[0028] (Acid leaching process) In the acid leaching process, the battery powder is brought into contact with an acidic leaching solution containing mineral or inorganic acids such as sulfuric acid, hydrochloric acid, or nitric acid to leach the battery powder. This dissolves mainly the metals in the battery powder, and a post-leaching solution containing these metals as metal ions is obtained. Here, a solution containing the metals in the battery powder as metal ions is called a metal-containing solution. The metal-containing solution includes the post-leaching solution obtained in the acid leaching process and sent to the next step, the pH raising process, as well as solutions taken during or between the pH raising process and each extraction process. Of the processes shown in Figure 1, the process from the acid leaching process to the hydroxide process described later is also called the wet process.

[0029] Regarding pH, the acidic leachate during leaching is preferably -0.5 to 3.0, while the post-leaching solution after leaching is complete may have a pH of 0.5 to 2.0. During leaching, for example, the acidic leachate may be stirred at 100 rpm to 400 rpm using a stirrer as needed, and the liquid temperature may be set to 50°C to 80°C, and further to 65°C to 70°C.

[0030] The metal-containing solution (post-leaching solution) obtained in the acid leaching process may have the following concentrations: cobalt ion concentration of 10 g / L to 50 g / L, nickel ion concentration of 10 g / L to 50 g / L, manganese ion concentration of 0 g / L to 50 g / L, lithium ion concentration of 3 g / L to 15 g / L, magnesium ion concentration of 0.001 g / L to 0.1 g / L, aluminum ion concentration of 1.0 g / L to 20 g / L, iron ion concentration of 0.1 g / L to 5.0 g / L, copper ion concentration of 0.005 g / L to 0.2 g / L, and fluorine concentration of 0.1 g / L to 5 g / L. The metal ion concentration in the solution can be confirmed by analysis using an ICP emission spectrometer.

[0031] (pH raising step) In the pH raising step, the pH of the metal-containing solution is increased, causing at least some of the aluminum ions and / or at least some of the iron ions in the metal-containing solution to precipitate and separate them from the metal-containing solution.

[0032] The pH raising process may include, for example, a dealuminizing process in which at least some of the aluminum ions are precipitated and removed by raising the pH of the metal-containing solution, and a deirradiating process in which an oxidizing agent is then added to oxidize the iron ions, and the pH is further raised as needed to precipitate and remove the iron ions. However, if the metal-containing solution is substantially free of iron ions, the deirradiating process may be omitted.

[0033] In the aluminum removal process and the iron removal process, the pH may be set within the range of 3.0 to 4.5. In the iron removal process, the ORP value during oxidation may be set to 300 mV to 900 mV. After precipitating aluminum in the aluminum removal process and after precipitating iron in the iron removal process, the neutralized residue as precipitate can be removed by solid-liquid separation such as filtration using known equipment and methods such as filter presses and thickeners.

[0034] In aluminum-free and iron-free processes, alkaline pH adjusters such as lithium hydroxide, sodium hydroxide, sodium carbonate, and ammonia can be used to raise the pH of the metal-containing solution. Among these, lithium hydroxide produced from lithium extracted by wet processing (such as the lithium hydroxide solution obtained after the hydroxide process described later) is preferred from the viewpoint of cost reduction. The oxidizing agent used in the iron-free process is not particularly limited as long as it can oxidize iron, but hydrogen peroxide, manganese dioxide, positive electrode active material, and / or manganese-containing leaching residue obtained by leaching the positive electrode active material are preferred.

[0035] (Manganese Extraction Process) After the pH-raising process, the metal-containing solution can be extracted and removed by solvent extraction to remove manganese ions, and possibly any remaining aluminum ions. In this case, the manganese ions and the remaining aluminum ions are extracted, resulting in a post-manganese extract solution from which they have been removed.

[0036] Here, phosphate ester extractants (such as di-2-ethylhexyl phosphate (abbreviation: D2EHPA or trade name: DP-8R)), or mixtures of phosphate ester extractants with aldoximes or oxime extractants mainly composed of aldoximes (such as 2-hydroxy-5-nonylacetophenone oxime (trade name: LIX84), 5-dodecylsalicylaldoxime (trade name: LIX860), a mixture of LIX84 and LIX860 (trade name: LIX984), 5-nonylsalicylaldoxime (trade name: ACORGAM5640)), etc.) can be used. The extractant may be diluted with a hydrocarbon organic solvent such as aromatic, paraffinic, or naphthenic solvent to a concentration of 10% to 30% by volume, and this may be used as the solvent.

[0037] During extraction, the equilibrium pH is preferably set to 2.3 to 3.5, more preferably to 2.5 to 3.0. From the viewpoint of cost reduction, it is preferable to use lithium hydroxide produced from lithium extracted by wet treatment (such as the lithium hydroxide solution obtained after the hydroxide step described later) as the alkaline pH adjusting agent used at this time, but lithium hydroxide or the like prepared separately may also be used.

[0038] For extraction, it is desirable to use a counter-flow multi-stage extraction method in which the flow directions of the aqueous phase and solvent used in each extraction are reversed. This suppresses the extraction of other metal ions such as cobalt ions, nickel ions, and lithium ions, and increases the extraction rate of manganese ions. When using a counter-flow multi-stage extraction method, it is effective to set the equilibrium pH during the first extraction stage to a value within the range mentioned above, and then increase the equilibrium pH during extraction with each subsequent stage. Counter-flow multi-stage extraction is also preferable in the cobalt extraction and nickel extraction processes described later.

[0039] (Cobalt Extraction Process) In the cobalt extraction process, cobalt ions are separated from the metal-containing solution obtained as a post-extraction liquid after the manganese extraction process by solvent extraction. Here, it is preferable to use a solvent containing a phosphonic acid ester extractant such as 2-ethylhexyl 2-ethylhexylphosphonate (trade names: PC-88A, Ionquest 801). The extractant may be diluted to 20% to 30% by volume with an organic solvent such as an aromatic, paraffinic, or naphthenic solvent to make a solvent, and this is also the case in other extraction processes.

[0040] During extraction, the equilibrium pH can be preferably set to 5.0 to 6.0, more preferably to 5.0 to 5.5. In this case, a pH adjusting agent containing lithium hydroxide is used. From the viewpoint of cost reduction, lithium hydroxide produced from lithium extracted by wet processing (such as the lithium hydroxide solution obtained after the hydroxide step described later) may be used as a pH adjusting agent, but in order to suppress the decrease in the purity of the cobalt salt, it is preferable to use commercially available lithium hydroxide or other relatively high-purity product prepared separately. By using a pH adjusting agent containing lithium hydroxide in the cobalt extraction step, the lithium ion concentration of the metal-containing solution in the wet processing can be maintained at a high level.

[0041] The solvent from which the cobalt ions were extracted may be scrubbed one or more times as needed (see Figure 3). The scrubbing solution can be, for example, a sulfuric acid solution, and the equilibrium pH during scrubbing can be set to 3.5 to 5.5.

[0042] As shown in Figure 3, the scrubbing solution generated during the cobalt extraction process can be mixed with a metal-containing solution and used for extraction in the same process. This allows for the recovery of cobalt ions distributed in the scrubbing solution, thereby minimizing losses. Since the cobalt extraction process uses a pH adjuster containing lithium hydroxide instead of sodium hydroxide, sodium contamination is suppressed even if the scrubbing solution is returned to the extraction.

[0043] Subsequently, back-extraction is performed against the solvent. The back-extract solution used for back-extraction can be any inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid, and the pH may be in the range of 2.0 to 4.0. The resulting back-extracted solution is then subjected to the cobalt re-extraction process described later.

[0044] For the solvent after back-extraction, scavenging can be performed to remove metals remaining in the solvent. In scavenging, an acidic aqueous solution such as sulfuric acid or hydrochloric acid is used, with an O / A ratio of 0.1 to 10 and a pH of about -1.0 to 1.0, and stirring and mixing may be performed with a mixer or the like at 200 rpm to 500 rpm for 5 to 60 minutes. Thereby, as shown in Figure 3, the solvent can be reused for extraction. Note that the broken line in Figure 3 represents the flow of the solvent. The scavenging in the cobalt re-extraction step described below can also be performed in substantially the same manner.

[0045] (Cobalt Re-extraction Step) The metal-containing solution obtained in the acid leaching step may contain magnesium ions in some cases. Although magnesium ions may be removed to some extent in the pH increasing step and the manganese extraction step, they may still be contained in the metal-containing solution supplied to the cobalt extraction step. In the cobalt extraction step, most magnesium ions are extracted into the solvent together with cobalt ions and then back-extracted, so they may be contained in the solution after back-extraction, which reduces the purity of the finally obtained cobalt salt. Therefore, in the present process, a cobalt re-extraction step is performed on the solution after back-extraction to remove magnesium ions.

[0046] The solution after back-extraction from the cobalt extraction step may have a magnesium ion concentration of, for example, 0.002 g / L to 1.000 g / L, typically 0.002 g / L to 0.550 g / L in some cases.

[0047] In the cobalt re-extraction step, a solvent containing a carboxylic acid-based extractant such as neodecanoic acid or naphthenic acid can be used. In particular, in order to extract cobalt ions without extracting magnesium ions as much as possible, a neodecanoic acid-based extractant, specifically Versatic Acid 10 (also referred to as VA-10) manufactured by Shell Chemicals, is preferable.

[0048] When a neodecanoic acid-based extractant is used, the equilibrium pH for extracting cobalt ions is preferably 6.5 to 7.5, more preferably 6.8 to 7.2. In the case of multi-stage extraction, the equilibrium pH during at least one stage of extraction, preferably during the first stage of extraction, can be set within the above range. Thereby, as described later, when the post-scrubbing solution containing sodium ions and magnesium ions is returned to the extraction step, most of the sodium ions and magnesium ions can be distributed into the raffinate. Even if a small amount of sodium ions and magnesium ions are distributed into the solvent, these can be removed by the scrubbing step described later.

[0049] The pH adjuster used for adjusting the equilibrium pH during extraction contains at least one of sodium hydroxide and potassium hydroxide. For example, when only lithium hydroxide such as the lithium hydroxide solution obtained in the hydroxylation step described later is used as a pH adjuster, most of the lithium ions derived from the lithium hydroxide are contained in the raffinate, and a large amount of lithium is lost when the raffinate is discarded. Further, if such a raffinate is subjected to electrodialysis in the hydroxylation step without being discarded, even if lithium loss can be suppressed, it leads to increased costs and decreased efficiency of electrodialysis. To address this, in this embodiment, a pH adjuster containing sodium hydroxide and / or potassium hydroxide is used in the cobalt re-extraction step. In particular, a pH adjuster containing sodium hydroxide can be suitably used.

[0050] When a pH adjuster containing sodium hydroxide is used, most of the sodium ions derived from sodium hydroxide contained in the pH adjuster migrate to the organic phase and are contained in the solvent during extraction. In contrast, in this embodiment, scrubbing is performed on the solvent after extraction. Thereby, sodium ions are removed from the solvent together with magnesium ions. In the case of multi-stage scrubbing, the equilibrium pH during scrubbing is preferably 5.5 to 6.5, more preferably 6.0 to 6.5 or 5.5 to 6.0 in at least one stage. The scrubbing solution used for scrubbing can contain cobalt ions, which increases the removal rate of sodium ions and magnesium ions.

[0051] The scrubbing solution contains not only sodium and magnesium ions, but also trace amounts of cobalt ions. To suppress cobalt loss, as shown in Figure 3, at least a portion of the scrubbing solution is subjected to the cobalt re-extraction process together with the back-extracted solution obtained in the cobalt extraction process. In this way, the cobalt ions contained in the scrubbing solution can be extracted and recovered again. If the scrubbing solution is returned to the cobalt extraction process instead of the cobalt re-extraction process, cobalt loss can be suppressed, but sodium ions in the scrubbing solution will be included as impurities in the cobalt extraction solution. In this embodiment, at least a portion of the scrubbing solution is returned to the cobalt re-extraction process, so such contamination can be avoided.

[0052] After scrubbing, back-extraction is performed using a back-extract solution containing sulfuric acid, hydrochloric acid, or nitric acid in the solvent. When generating cobalt sulfate in the crystallization step described later, it is preferable to use a sulfuric acid back-extract solution. The equilibrium pH during back-extraction is preferably 1.0 to 4.0, and more preferably 1.5 to 2.0. The cobalt solution obtained as a back-extracted solution will have a sufficiently reduced magnesium ion concentration, for example, to 0.001 g / L to 0.002 g / L. Therefore, the cobalt salt (cobalt sulfate, cobalt hydrochloride, or cobalt nitrate, etc.) crystallized by heating and concentrating this cobalt solution, for example, at 40°C to 120°C, will be of high purity with almost no magnesium content.

[0053] It is preferable to use at least a portion of the post-crystallization solution separated from the cobalt salt after crystallization as at least a portion of the scrubbing solution in the cobalt extraction process, as shown in Figure 3. The post-crystallization solution contains cobalt ions and can be used as a scrubbing solution. By using the post-crystallization solution as at least a portion of the scrubbing solution, it becomes unnecessary to prepare a large amount of new scrubbing solution. Furthermore, it is preferable to mix at least a portion of the post-scrubbing solution obtained in the cobalt extraction process with a metal-containing solution (in this example, the post-extraction solution from the manganese extraction process) and use it for extraction in the cobalt extraction process, as shown in Figure 3. This makes it possible to recover the cobalt ions contained in the post-scrubbing solution.

[0054] Furthermore, at least a portion of the post-crystallization solution generated during the crystallization of cobalt salt may be mixed with a metal-containing solution (in this example, the post-extraction solution from the manganese extraction step) and subjected to the extraction in the cobalt extraction step, without undergoing scrubbing in the cobalt extraction step. In this way, cobalt ions can be recovered from the post-crystallization solution.

[0055] As mentioned earlier, when the scrubbing solution is returned to the extraction process in the cobalt re-extraction step, the sodium ions contained in it are effectively removed by the extraction and scrubbing. Therefore, the crystallized solution often contains virtually no sodium ions, and even when it is returned to the extraction and scrubbing process in the cobalt extraction step as described above, contamination by sodium is unlikely to occur.

[0056] The solvent after back-extraction can be scavenged to remove any remaining metals. The resulting scavenged solution is preferably used as at least a portion of the acid leaching solution in the acid leaching process. Because the scavenged solution has a low pH, it can be used as an acid by returning it to the acid leaching process. Furthermore, returning it to the acid leaching process allows for the recovery of any cobalt ions that may be present in the scavenged solution.

[0057] (Nickel Extraction Process) In the nickel extraction process, nickel ions are separated from the metal-containing solution obtained as a post-extraction liquid after the extraction of cobalt ions by solvent extraction. As the solvent, solvents containing carboxylic acid-based extractants such as neodecanoic acid and naphthenic acid can be used.

[0058] The equilibrium pH during extraction is preferably 6.0 to 8.0, more preferably 6.8 to 7.2. While lithium hydroxide produced from lithium extracted by wet processing (such as the lithium hydroxide solution obtained after the hydroxide step described later) may be used as the pH adjusting agent to reduce costs, it is preferable to use commercially available lithium hydroxide or other relatively high-purity products prepared separately to suppress a decrease in the purity of the nickel salt.

[0059] After scrubbing the solvent from which nickel ions have been extracted, back-extraction can be performed using a back-extract solution containing sulfuric acid, hydrochloric acid, or nitric acid, for example, at a pH of 1.0 to 3.0. Subsequently, the back-extracted solution can be electrolyzed and dissolved as needed, then heated and concentrated to crystallize the nickel ions as nickel salts (nickel sulfate, nickel hydrochloric acid, or nickel nitrate, etc.).

[0060] At least a portion of the lithium-containing solution after nickel ions have been extracted may be mixed with the acidic leaching solution in the acid leaching step. This allows the lithium ions contained in the lithium-containing solution to be circulated throughout the series of steps from the acid leaching step to the nickel extraction step. Preferably, after the lithium ion concentration in the lithium-containing solution has increased to a certain extent by circulating the lithium ions in this way, the hydroxide step described below can be carried out.

[0061] (Hydroxide process) The lithium-containing solution obtained from the extractant solution of the cobalt extraction process via the nickel extraction process contains substantially only lithium ions, as a result of the separation of manganese ions, cobalt ions, and nickel ions in each of the extraction processes described above. In the hydroxide process, the above lithium-containing solution (lithium sulfate solution, etc.) is subjected to hydroxide treatment using various methods described below to produce a lithium hydroxide solution.

[0062] For example, a lithium carbonate solution can be obtained by first adding a carbonate to a lithium sulfate solution or by blowing in carbon dioxide. Then, using a so-called chemical conversion method, calcium hydroxide can be added to the lithium carbonate solution, and a lithium hydroxide solution can be produced according to the reaction equation Li₂CO₃ + Ca(OH)₂ → 2LiOH + CaCO₃. Calcium ions that may remain in the solution can be removed using cation exchange resins or chelating resins.

[0063] Alternatively, a lithium hydroxide solution can be obtained by adding barium hydroxide to a lithium sulfate solution and following the reaction Li₂SO₄ + Ba(OH)₂ → 2LiOH + BaSO₄. The barium that may dissolve in the solution at this time can be separated and removed using a cation exchange resin or chelating resin.

[0064] Alternatively, when employing the so-called electrolytic method, a lithium hydroxide solution can be generated on the cathode side by supplying a lithium sulfate solution to the anode side and performing electrolysis in an electrolytic cell equipped with a cation exchange membrane that separates the anode side and the cathode side.

[0065] In this electrolytic method, a lithium sulfate solution is sometimes supplied to the desalination chamber between the anion exchange membrane and the cation exchange membrane in a bipolar membrane electrodialysis machine, and electrodialysis is performed. In this case, a lithium hydroxide solution may be obtained in the alkaline chamber between the cation exchange membrane and the bipolar membrane, while an acidic solution such as sulfuric acid may be obtained in the acidic chamber between the bipolar membrane and the anion exchange membrane.

[0066] Furthermore, lithium-containing solutions may contain trace amounts of cations such as nickel and magnesium ions that were not completely separated during the extraction process. Nickel and magnesium ions are cations, just like lithium ions, and exhibit similar behavior during electrodialysis, making them difficult to separate from lithium ions. In addition, performing electrodialysis on a lithium-containing solution containing nickel and magnesium ions may generate nickel and magnesium hydroxides in the resulting lithium hydroxide solution, raising concerns that electrodialysis may become impossible due to process problems. For this reason, it is desirable to wash the lithium-containing solution to remove cations such as nickel and magnesium ions prior to electrodialysis. For example, ion exchange resins or chelate resins can be used for this washing.

[0067] The lithium hydroxide solution obtained as described above can be effectively used as an alkaline pH adjuster in at least one of the following steps: the pH raising step, the manganese extraction step, the cobalt extraction step, and the nickel extraction step.

[0068] (Crystalling process) The lithium hydroxide solution obtained in the hydroxide process can be subjected to the crystallization process. For example, as described above, if the lithium hydroxide solution is returned to the wet process as a pH adjuster, the lithium ion concentration in the solution may gradually increase due to the lithium in the battery powder newly added to the wet process. The crystallization process may be carried out according to the lithium ion concentration to recover the lithium hydroxide.

[0069] In the crystallization process, crystallization operations such as heating and concentration or vacuum distillation can be performed to precipitate lithium hydroxide. In the case of heating and concentration, a higher temperature during crystallization is preferable as it speeds up the process. However, after crystallization, the temperature at which the precipitate is dried should preferably be below 60°C to prevent the desorption of crystal water. This is because anhydrous lithium hydroxide from which crystal water has been desorbed is hygroscopic and difficult to handle. The lithium hydroxide produced in the crystallization process may be subjected to pulverization or other treatments to adjust its physical properties to the required level.

[0070] (Potential Contribution to SDGs) According to the embodiment described above, it is possible to reduce costs and suppress metal loss when recovering metals from lithium-ion battery waste. For this reason, this embodiment has the potential to contribute to Goal 9, "Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation," and Goal 12, "Ensure sustainable consumption and production patterns," of the United Nations-led Sustainable Development Goals (SDGs).

Claims

1. A method for recovering metal from lithium-ion battery waste, comprising: a cobalt extraction step, which includes extracting cobalt ions into a solvent and back-extracting cobalt ions from the solvent in this order, with respect to a metal-containing solution obtained by leaching metal from the battery powder of lithium-ion battery waste and containing cobalt ions; and a cobalt re-extraction step, which includes extracting cobalt ions into a solvent, scrubbing the solvent, and back-extracting cobalt ions from the solvent in this order, with respect to the back-extracted solution obtained in the cobalt extraction step, wherein a pH adjusting agent containing lithium hydroxide is used in the cobalt extraction step, a pH adjusting agent containing at least one of sodium hydroxide and potassium hydroxide is used in the cobalt re-extraction step, and at least a portion of the scrubbing solution obtained in the scrubbing of the cobalt re-extraction step and containing cobalt ions and sodium ions is subjected to the extraction in the cobalt re-extraction step together with the back-extracted solution obtained in the cobalt extraction step.

2. The metal recovery method according to claim 1, wherein the solvent used in the cobalt re-extraction step includes a neodecanoic acid-based extractant.

3. The metal recovery method according to claim 2, wherein the equilibrium pH at the time of extraction in the cobalt re-extraction step is set to 6.5 to 7.

5.

4. The metal recovery method according to claim 3, comprising an acid leaching step of leaching the metal in the battery powder into an acidic leaching solution, wherein the cobalt re-extraction step includes scavenging the solvent after the back-extraction, and at least a portion of the post-scavenging solution obtained by the scavenging is used as at least a portion of the acidic leaching solution in the acid leaching step.

5. The metal recovery method according to claim 3, further comprising a crystallization step to obtain a cobalt salt from the cobalt solution obtained in the back extraction step of the cobalt re-extraction step.

6. The metal recovery method according to claim 5, wherein the cobalt extraction step includes scrubbing the solvent between the extraction and the back extraction, at least a portion of the post-crystallization solution obtained in the crystallization step is used in the scrubbing of the cobalt extraction step, and at least a portion of the post-scrubbing solution obtained in the scrubbing of the cobalt extraction step is used together with the metal-containing solution for the extraction of the cobalt extraction step.

7. The metal recovery method according to claim 5, wherein at least a portion of the post-crystallization liquid obtained in the crystallization step is subjected to the extraction in the cobalt extraction step together with the metal-containing solution.

8. The metal recovery method according to claim 1, wherein the cobalt extraction step includes scrubbing the solvent between the extraction and the back extraction, and at least a portion of the scrubbed liquid obtained in the scrubbing of the cobalt extraction step is subjected to the extraction of the cobalt extraction step together with the metal-containing solution.

9. A metal recovery method according to claim 1, comprising a hydroxide step of hydroxylating a lithium-containing solution obtained from the extractive solution of the cobalt extraction step to obtain a lithium hydroxide solution, wherein the lithium hydroxide in the lithium hydroxide solution is included in at least one of the pH adjusting agents used in the wet treatment, which is used in the cobalt extraction step.

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