Metal recycling methods

Abstract

When lithium is circulated in the liquid in a series of steps, an increase in the sodium concentration can be effectively suppressed. A method for recovering metals from battery powder of lithium-ion battery waste, the method comprising: an acid leaching step in which metals, including lithium, sodium, and the metal to be separated, in the battery powder are leached into an acidic leaching solution to obtain a metal-containing solution containing the metal; and a metal separation step in which the metal to be separated is separated from the metal-containing solution; the method further comprises a liquid removal step in which, after the metal separation step, lithium in the lithium-containing solution obtained after the metal separation step is returned to the acid leaching step and / or the metal separation step, thereby circulating lithium within a series of steps including the acid leaching step and the metal separation step, and removing a portion of the lithium-containing solution containing sodium.

Description

Technical Field

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

Background Art

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

[0003] To recover valuable metals from lithium-ion battery waste, for example, wet treatment is performed on battery powder obtained through roasting or other predetermined dry pretreatment of lithium-ion battery waste. In wet treatment, specifically, metals such as cobalt, nickel, manganese, lithium, aluminum, and iron in the battery powder are leached with an acid to obtain a metal-containing solution in which the metal is dissolved. Next, as described in Patent Document 1 for example, aluminum, iron, manganese, etc. among the elements dissolved in the metal-containing solution are sequentially or simultaneously removed by neutralization or solvent extraction. Thereafter, cobalt and nickel in the metal-containing solution are separated and concentrated by solvent extraction. After nickel is separated by extraction, a lithium-containing solution in which lithium is dissolved and remains is obtained. For the lithium-containing solution thus obtained, lithium ions are concentrated by repeating solvent extraction or the like, and then carbonation is performed by adding carbonate or blowing carbon dioxide gas or the like, so that the lithium ions contained in the lithium-containing solution are recovered as lithium carbonate.

[0004] Regarding such metal recovery methods, Patent Documents 2 and 3 describe a method for recovering metal from lithium-ion battery waste that "suppresses the use of sodium hydroxide as a pH adjuster and efficiently recovers metal from lithium-ion battery waste," which includes a wet treatment in which lithium-containing metals in lithium-ion battery waste are leached with acid, and the metals are extracted from the metal-containing solution in which the metals have dissolved, and the lithium extracted in the wet treatment is used as a pH adjuster in the wet treatment. Furthermore, Patent Documents 2 and 3 describe a method in which "a series of steps including an acid leaching step, a manganese extraction step, a cobalt extraction step, a nickel extraction step, and a hydroxide step are repeated multiple times, and at least a portion of the lithium is circulated in the liquid during the series of steps." [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 6801090 [Patent Document 2] Patent No. 7100211 [Patent Document 3] Patent No. 7100217 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Incidentally, lithium-ion battery waste and the battery powder obtained therefrom may contain sodium. This sodium, along with metals such as lithium in the battery powder, is leached out with acid and included in the metal-containing solution, where it exhibits similar behavior to lithium in wet processing.

[0007] Therefore, as described in Patent Documents 2 and 3, when lithium is circulated in a series of processes, as battery powder is introduced into the wet treatment, not only the lithium concentration but also the sodium concentration in the liquid gradually increases. This increase in sodium concentration leads to a decrease in the quality of lithium recovered by the metal recovery method.

[0008] This specification provides a metal recovery method that can effectively suppress the increase in sodium concentration when lithium is circulated in a liquid during a series of processes. [Means for solving the problem]

[0009] The metal recovery method disclosed in this specification is a method for recovering metal from battery powder of lithium-ion battery waste, comprising: an acid leaching step of leaching metals including lithium, sodium, and a metal to be separated in the battery powder into an acidic leaching solution to obtain a metal-containing solution containing the metals; a metal separation step of separating the metal to be separated from the metal-containing solution; returning the lithium in the lithium-containing solution obtained after the metal separation step to the acid leaching step and / or the metal separation step, circulating the lithium within a series of steps including the acid leaching step and the metal separation step; and further comprising a deliquidation step of removing a portion of the lithium-containing solution containing sodium after the metal separation step. [Effects of the Invention]

[0010] According to the metal recovery method described above, the increase in sodium concentration when lithium is circulated in the liquid during a series of processes can be effectively suppressed. [Brief explanation of the drawing]

[0011] [Figure 1] A flowchart illustrating an example of a process to which the metal recovery method of one embodiment can be applied. [Figure 2] This flowchart shows an example of a case where a deliquidation step is performed on the lithium-containing solution in the process shown in Figure 1, according to one embodiment of the metal recovery method. [Figure 3] This is a flowchart illustrating an example of the steps involved in obtaining battery powder from lithium-ion battery waste. [Modes for carrying out the invention]

[0012] 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 battery powder, which is a waste product of lithium-ion batteries. This method includes an acid leaching step in which lithium and metals to be separated in the battery powder are leached in an acidic leaching solution to obtain a metal-containing solution containing these metals as metal ions, and a metal separation step in which the metals to be separated are separated from the metal-containing solution.

[0013] Here, as illustrated in Figure 1, the lithium in the lithium-containing solution obtained after the metal separation step is returned to the acid leaching step and / or metal separation step in the form of lithium sulfate solution or lithium hydroxide solution, and lithium is circulated within a series of steps including the acid leaching step and the metal separation step. The lithium hydroxide solution mentioned above can be used as a pH adjuster in the metal separation step. By circulating lithium, it is possible to maintain a high lithium concentration in the solution throughout the series of steps, and in some cases, all the pH adjusters required in the metal separation step can be supplied by the lithium hydroxide solution mentioned above. Lithium hydroxide may be recovered from any remaining lithium hydroxide solution.

[0014] Incidentally, battery powder sometimes contains sodium. This sodium is leached out during the acid leaching process and included in the metal-containing solution. It is not separated along with lithium during the metal separation process and is included in the subsequent lithium-containing solution. In this case, as mentioned above, if the process of returning lithium from the lithium-containing solution to the acid leaching process and the metal separation process to circulate the lithium is repeated, the concentration of sodium as well as lithium in the solution increases throughout the series of processes. Sodium present in high concentrations in the solution can, for example, contaminate the lithium hydroxide obtained in the crystallization process, degrading its quality.

[0015] To address this, in this embodiment, after the metal separation step, a desorption step is performed to remove a portion of the lithium-containing solution containing sodium, as shown in Figure 2. The remaining lithium-containing solution after the desorption step is returned to the series of steps and used for lithium recycling. By performing the desorption step, a portion of the sodium in the lithium-containing solution after the metal separation step is removed, thereby suppressing an increase in sodium concentration. As a result, the decrease in the quality of lithium hydroxide produced in the crystallization step can be effectively suppressed.

[0016] In the example shown in Figure 1, the purification step, hydroxide step, and crystallization step are performed in this order after the metal separation step, and these steps are also included in the series of steps. In Figure 1, the metal separation step is specifically composed of a neutralization step, a manganese extraction step, a cobalt extraction step, and a nickel extraction step, but at least one of these steps can be omitted, or another step can be added. Furthermore, battery powder can be obtained by performing pretreatment steps such as roasting, crushing, and sieving on lithium-ion battery waste, as illustrated in Figure 3. This explanation follows Figures 1 to 3, but Figures 1 to 3 are illustrative and not limited to such specific flows.

[0017] (Lithium-ion battery waste) The lithium-ion battery waste targeted is lithium-ion secondary batteries that can be used in mobile phones and various other electronic devices, and that 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 perspective of effective resource utilization. Lithium-ion battery waste refers to lithium-ion batteries that are subject to recycling, regardless of whether the lithium-ion batteries are traded for a price, free of charge, or treated as industrial waste.

[0018] Lithium-ion battery waste has a housing containing aluminum as an exterior that wraps around it. Examples of such a housing include those made of only aluminum, or those containing aluminum and iron, aluminum laminate, etc. Further, the lithium-ion battery waste contains, within the above housing, a positive electrode active material composed of a single metal oxide containing lithium and one kind selected from the group consisting of nickel, cobalt, and manganese, or a composite metal oxide containing two or more kinds, etc. The positive electrode active material may include an aluminum foil (positive electrode substrate) coated and fixed with, for example, polyvinylidene fluoride (PVDF) or other organic binders. In addition, copper, iron, etc. may be contained in the lithium-ion battery waste. Further, the housing of the lithium-ion battery waste usually contains an electrolyte solution in which an electrolyte such as lithium hexafluorophosphate is dissolved in an organic solvent. Examples of the organic solvent that may be used include ethylene carbonate, diethyl carbonate, etc.

[0019] (Pretreatment step) In many cases, a pretreatment step as a dry treatment is performed on lithium-ion battery waste. The pretreatment step may include at least one of roasting, crushing, and sieving. Lithium-ion battery waste becomes battery powder through the pretreatment step. The roasting, crushing, and sieving in the pretreatment step may each be performed as necessary, or may be performed in any order. Battery powder means powder in which the positive electrode material component is separated and concentrated by performing some pretreatment on lithium-ion battery waste. Battery powder may also be obtained as a powdery material in which the positive electrode material component is concentrated by performing crushing and sieving on lithium-ion battery waste with or without heat treatment.

[0020] In roasting, the above lithium-ion battery waste is heated. When roasting is performed, for example, metals such as lithium and cobalt contained in the lithium-ion battery waste can change into a form that is easily melted. During roasting, it is preferable to heat the lithium-ion battery waste while holding it in a temperature range of, for example, 450°C to 1000°C, preferably 600°C to 800°C, for 0.5 hours to 4 hours. In roasting, either heating in an air atmosphere or heating in an inert atmosphere such as nitrogen can be performed, or both heating in an air atmosphere and heating in an inert atmosphere can be performed in this sequential order or in the reverse order. The roasting furnace may be a batch type or a continuous type. For example, in the batch type, there is a stationary furnace, and in the continuous type, there is a rotary kiln furnace, etc., and various other furnaces can also be used.

[0021] During roasting, at least a part of the electrolyte is removed from the lithium-ion battery waste due to evaporation of the electrolyte or the like. In many cases, when the lithium-ion battery waste is heated during roasting, the low-boiling components in the internal electrolyte components evaporate sequentially from the lowest boiling point. When roasting is performed, the electrolyte is removed and rendered harmless, and the organic binder is decomposed, promoting the separation of the aluminum foil and the positive electrode active material during the subsequent crushing and sieving. Although the composition of the positive electrode active material changes due to roasting, here, even after roasting, it will be referred to as the positive electrode active material.

[0022] After roasting, crushing can be performed to remove the positive electrode active material and the like from the casing of the lithium-ion battery waste. 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.

[0023] Various known devices or equipment can be used for crushing, but it is particularly preferable to use an impact-type crusher that can crush 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. A screen can be installed at the outlet of the crusher, so that the lithium-ion battery waste is crushed to a size that can pass through the screen and then discharged from the crusher through the screen.

[0024] After crushing the lithium-ion battery waste, sieving is performed using a sieve with an appropriate mesh size. This allows for obtaining battery powder with aluminum and copper remaining on the sieve surface, and aluminum and copper removed to some extent on the underside.

[0025] The battery powder obtained in the pretreatment step contains nickel, cobalt, lithium, manganese, etc. For example, the nickel content of the battery powder is 1% to 30% by mass, the cobalt content is 1% to 30% by mass, the lithium content is 2% to 8% by mass, and the manganese content is 1% to 30% by mass, but is not limited to these. The battery powder may further contain aluminum at 1% to 10% by mass, iron at 1% to 5% by mass, copper at 1% to 10% by mass, and sodium at 0.001% to 0.1% by mass. In this embodiment, the battery powder containing lithium, sodium, and the metal to be separated is targeted. The metal to be separated may include at least one selected from the group consisting of nickel, cobalt, manganese, aluminum, iron, and copper.

[0026] (Acid leaching process) In the acid leaching process, metals in the battery powder are leached out using an acidic leaching solution such as sulfuric acid. This yields a solution in which the metals in the battery powder are dissolved, as well as any remaining leaching residue. Here, the solution in which the metals in the battery powder are dissolved in each step from the completion of the acid leaching process to the nickel extraction process described later is also referred to as the metal-containing solution.

[0027] In the acid leaching process, the pH of the acidic leached solution and the post-leached solution may be less than 3.5. The oxidation-reduction potential (ORP value, based on silver / silver chloride potential) may also be 100 mV or less. After leaching is complete, solid-liquid separation may be performed to separate the leached residue from the metal-containing solution; however, solid-liquid separation may be omitted, and the metal-containing solution containing the leached residue may be used in the subsequent neutralization process. As a diluent to adjust the pH of the acidic leached solution, the post-extraction solution from the nickel extraction process (such as lithium sulfate solution) or water can be used, as described later. This allows lithium to circulate within the series of steps in the wet treatment process, and the lithium in the solution can be concentrated within that process.

[0028] The metal-containing solution obtained in the acid leaching process may have concentrations such as nickel (10 g / L to 50 g / L), cobalt (5 g / L to 50 g / L), lithium (2 g / L to 10 g / L), manganese (0 g / L to 50 g / L), aluminum (1.0 g / L to 20 g / L), iron (0.1 g / L to 5.0 g / L), copper (0.005 g / L to 0.2 g / L), and sodium (0.001 g / L to 0.1 g / L).

[0029] (neutralization process) If the metal-containing solution obtained in the acid leaching process contains aluminum and / or iron, a neutralization step can be performed at the beginning of the metal separation process to raise the pH of the metal-containing solution and separate the neutralization residue to obtain the neutralized solution. The neutralization process may include a dealuminizing step and a deiraging step. However, if the metal-containing solution does not contain aluminum and / or iron, the dealuminizing step and / or deiraging step may be omitted.

[0030] In the dealuminization stage, at least a portion of the aluminum is precipitated by increasing the pH of the metal-containing solution and then removed by solid-liquid separation. At this time, for example, if the pH is raised to a range of 4.0 to 5.0 using a pH adjusting agent at a liquid temperature of 50°C to 90°C, aluminum can be effectively separated while suppressing the precipitation of nickel and / or cobalt.

[0031] In the iron removal stage, an oxidizing agent is added, and then a pH adjuster is added to raise the pH to within the range of 4.0 to 5.0. This oxidizes the iron from divalent to trivalent, causing it to precipitate as an oxide or solid such as iron hydroxide (Fe(OH)3), which can then be removed by solid-liquid separation. The oxidation-reduction potential (ORP value, based on silver / silver chloride potential) during oxidation is preferably 300mV to 900mV. The oxidizing agent is not particularly limited as long as it can oxidize iron, but manganese dioxide, positive electrode active material, and / or manganese-containing leaching residue obtained by leaching the positive electrode active material are preferred. 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 is used as the oxidizing agent, a precipitation reaction occurs in which manganese dissolved in the liquid becomes manganese dioxide, and the precipitated manganese can be removed together with the iron.

[0032] Examples of pH adjusting agents used in neutralization steps such as the aluminum removal and iron removal steps mentioned above include solid or liquid lithium hydroxide, sodium hydroxide, sodium carbonate, and ammonia. Among these, lithium hydroxide is preferred because it prevents contamination of the lithium hydroxide recovered in the crystallization step described later with sodium and other substances. The pH adjusting agent can be the lithium hydroxide solution obtained in the hydroxide step or the post-crystallization solution (lithium hydroxide solution) obtained in the crystallization step, thereby circulating lithium throughout the series of steps.

[0033] (Manganese extraction process) After the neutralization step described above, the metal-containing solution can be neutralized as needed, and then manganese can be extracted and removed by solvent extraction. In this process, if aluminum remains in the metal-containing solution, both manganese and aluminum will be extracted and removed.

[0034] For manganese extraction, it is preferable to use an extractant containing a phosphate ester extractant. A specific example of a phosphate ester extractant is di-2-ethylhexyl phosphate (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 whose main component is an aldoxime. Specifically, examples include 2-hydroxy-5-nonylacetophenone oxime (trade name: LIX84), 5-dodecylsalicylaldoxime (trade name: LIX860), a mixture of LIX84 and LIX860 (trade name: LIX984), and 5-nonylsalicylaldoxime (trade name: ACORGAM5640).

[0035] The extractant may be diluted with a hydrocarbon-based organic solvent such as aromatic, paraffinic, or naphthenic solvents to a concentration of 10% to 30% by volume, and this diluted solvent may be used as the solvent.

[0036] During extraction, the equilibrium pH is preferably set to 2.3 to 3.5, more preferably 2.5 to 3.0. A lithium hydroxide solution is preferred as the pH adjusting agent used at this time; for example, a lithium hydroxide solution obtained in the hydroxide step or crystallization step described later can be used.

[0037] Extraction, as an example, involves contacting a solution (aqueous phase) and a solvent (organic phase), and typically stirring and mixing them in a mixer for, for example, 5 to 60 minutes to react the metal with the extractant. The extraction temperature is set to room temperature (around 15 to 25°C) to 60°C or lower, and is preferably carried out at 35 to 45°C due to the extraction rate, phase separation, and evaporation of the organic solvent. After that, the mixed organic phase and aqueous phase are separated by the difference in specific gravity using a settler. Extraction in processes other than manganese extraction can be carried out in substantially the same manner.

[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 method suppresses the extraction of cobalt, nickel, and lithium while increasing the manganese extraction rate. 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 lower the equilibrium pH during each subsequent extraction stage.

[0039] In the metal-containing solution after the manganese extraction process, for example, the cobalt concentration may be 0 g / L to 50 g / L, the nickel concentration 0 g / L to 50 g / L, the lithium concentration 1 g / L to 30 g / L, and the sodium concentration 0.001 g / L to 0.1 g / L.

[0040] (Cobalt extraction process and crystallization process) After extracting manganese, cobalt can be extracted and separated from the metal-containing solution by solvent extraction.

[0041] For cobalt extraction, it is preferable to use a solvent containing a phosphate-based extractant, particularly a phosphonic acid ester extractant. Ethylhexyl 2-ethylhexylphosphonate (trade names: PC-88A, Ionquest801) is especially preferred from the viewpoint of nickel-cobalt separation efficiency. The extractant can be diluted with a hydrocarbon-based organic solvent to a concentration of 10% to 30% by volume and used as the solvent.

[0042] When extracting cobalt, the equilibrium pH during extraction should preferably be 5.0 to 6.0, more preferably 5.0 to 5.5. If the pH is lower than 5.0, there is a risk that the cobalt may not be sufficiently extracted into the solvent. In this case, it is preferable to use a lithium hydroxide solution as a pH adjuster, for example, a lithium hydroxide solution obtained in the hydroxide step or crystallization step described later can be used.

[0043] When extracting cobalt, 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 method suppresses the extraction of nickel and lithium while increasing the extraction rate of cobalt.

[0044] During the extraction process described above, small amounts of nickel and lithium may be extracted into the solvent in addition to cobalt. In this case, if necessary, the solvent from which cobalt was extracted may be scrubbed once or more times using a scrubbing solution to remove any nickel or lithium that may be present in the solvent. The scrubbing solution can be, for example, a sulfuric acid solution with a pH of 3.5 to 5.5. The post-scrubbing solution may contain nickel and lithium. Therefore, it is desirable to mix some or all of the post-scrubbing solution with the metal-containing solution from the manganese extraction process and use this as the pre-extraction solution for the cobalt extraction process. This allows nickel and lithium to be circulated or retained within the series of processes without loss. However, if the solvent from which cobalt was extracted does not contain nickel or lithium, scrubbing may not be necessary.

[0045] Subsequently, back-extraction is performed using a solvent containing cobalt. The back-extract solution used can be any inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid, but sulfuric acid is preferable if sulfate is to be obtained in the subsequent crystallization step. Here, the pH conditions should be such that as much of the cobalt as possible migrates from the solvent to the back-extract solution. Specifically, the pH is preferably in the range of 2.0 to 4.0, and more preferably in the range of 2.5 to 3.5.

[0046] A crystallization process can be performed on the back-extracted solution. In the crystallization process, the back-extracted solution is heated to, for example, 40°C to 120°C to concentrate it. This causes the cobalt to crystallize, yielding cobalt salts such as cobalt sulfate. The cobalt salts obtained in this way have a nickel content of preferably 5 ppm by mass or less, and since the nickel has been sufficiently removed, they can be effectively used as raw materials for the manufacture of lithium-ion secondary batteries and other batteries. However, the crystallized solution may contain cobalt and lithium that did not crystallize. Therefore, it is desirable to mix the crystallized solution with the back-extracted solution before the crystallization process and use it for another crystallization process, or to use it to adjust the cobalt concentration of the scrubbing solution used as the solvent for extracting cobalt, or to mix it with the metal-containing solution after the manganese extraction process and use it for the cobalt extraction process. In this way, cobalt and lithium can be circulated or retained and concentrated within a series of processes without loss.

[0047] (Nickel extraction process and crystallization process) The metal-containing solution remaining after cobalt extraction in the cobalt extraction process mainly contains nickel and lithium. To recover nickel from this metal-containing solution, a solvent extraction method can be used to extract nickel into a solvent.

[0048] A mixer-settler may be used for extraction. In this case, first, the pH is adjusted, for example, by adding a pH adjuster to the solvent. Then, the metal-containing solution (aqueous phase) and the solvent (organic phase) are mixed in the mixer to form a mixture, which is then stirred. At this time, nickel in the metal-containing solution migrates to the solvent. After that, the mixture is allowed to stand in the settler, and the aqueous phase and the organic phase are separated based on their specific gravity difference. This yields the extracted solution from which the solvent has been separated.

[0049] The solvent used in the nickel extraction process preferably contains a carboxylic acid-based extractant. Examples of carboxylic acid-based extractants include neodecanoic acid and naphthenic acid, but neodecanoic acid (such as Versatic Acid 10 (VA-10) manufactured by Shell Chemical Corporation) is preferred due to its nickel extraction ability. The extractant may be diluted using hydrocarbon-based organic solvents such as aromatic, paraffinic, or naphthenic solvents to a concentration of 10% to 30% by volume, and this may be used as the solvent.

[0050] The equilibrium pH during extraction is preferably 6.0 to 8.0, more preferably 6.8 to 7.2. A lithium hydroxide solution is preferred as the pH adjusting agent used at this time; for example, a lithium hydroxide solution obtained in the hydroxide step or crystallization step described later can be used.

[0051] Extraction should preferably be carried out in multiple stages using a counter-flow method, where the flow directions of the metal-containing solution and the solvent are opposite. This suppresses the extraction of lithium into the solvent and increases the extraction rate of nickel. When using a multi-stage counter-flow extraction method, it is effective to set the equilibrium pH during the first extraction stage to a value within the aforementioned range, and then lower the equilibrium pH during each subsequent extraction stage.

[0052] For solvents that have become nickel-containing after extraction, scrubbing may be performed one or more times using a scrubbing solution to remove any lithium that may be present in the solvent, if necessary. The scrubbing solution can be, for example, a sulfuric acid solution with a pH of 5.0 to 6.0. Here, the post-scrubbing solution may contain lithium. Therefore, it is desirable to mix part or all of the post-scrubbing solution with the metal-containing solution after the cobalt extraction step and use this as the pre-extraction solution for the nickel extraction step. This allows for the concentration of lithium by circulating or retaining it within the series of steps without loss. However, if the nickel-containing solvent does not contain lithium, scrubbing may not be necessary.

[0053] Subsequently, back-extraction is performed using a nickel-containing solvent. The back-extract solution used can be any inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid, but sulfuric acid is preferable if sulfate is to be obtained in the subsequent crystallization step. The pH is preferably in the range of 1.0 to 3.0, and more preferably 1.5 to 2.5. The O / A ratio and the number of times can be determined as appropriate, but the O / A ratio is 5 to 1, more preferably 4 to 2.

[0054] When a back-extraction solution such as nickel sulfate solution is obtained by back-extraction, electrolysis and dissolution can be performed as needed, and then the solution can be heated to 40°C to 120°C in the crystallization step to crystallize nickel as nickel salts such as nickel sulfate. This yields nickel salts. However, the crystallized solution may contain uncrystallized nickel and lithium. Therefore, it is desirable to mix the crystallized solution with the back-extraction solution before the crystallization step and use it for another crystallization step, to use it to adjust the nickel concentration of the scrubbing solution in a nickel-containing solvent, or to mix it with the metal-containing solution after the cobalt extraction step and use it for the nickel extraction step. In this way, nickel and lithium can be circulated or retained and concentrated within the series of steps without loss.

[0055] The post-extraction solution (such as lithium sulfate solution) after nickel has migrated to the solvent mainly contains lithium and may be added to the acidic leaching solution in the acid leaching step. This allows the lithium contained in the post-extraction solution to be circulated throughout the series of steps. Preferably, after the lithium concentration in the post-extraction solution has increased to a certain extent by circulating the lithium in this way, the hydroxide step described later can be carried out.

[0056] (liquid purification process) The lithium-containing solution (such as lithium sulfate solution), which is the post-extraction liquid from the nickel extraction process described above, may contain trace amounts of cations such as nickel and magnesium that were not completely separated in the metal separation process. Nickel and magnesium are cations, just like lithium, and exhibit similar behavior to lithium during electrodialysis in the hydroxide process described later, making them difficult to separate from lithium. Furthermore, if electrodialysis is performed on a metal-containing solution containing nickel and magnesium, nickel and magnesium hydroxides may be generated in the resulting lithium hydroxide solution, raising concerns that electrodialysis may become unsustainable due to process problems.

[0057] Therefore, in such cases, it is desirable to perform a purification process to remove cations such as nickel and magnesium from the lithium-containing solution prior to the hydroxide process. For example, an ion exchange resin or a chelating resin can be used as this purification solution. However, if the lithium-containing solution obtained in the nickel extraction process does not contain nickel, magnesium, etc., the purification process may be omitted.

[0058] (Hydroxylation process) In the hydroxide process, a lithium-containing solution, such as a lithium sulfate solution, is subjected to a hydroxide treatment to produce a lithium hydroxide solution. The details of the hydroxide treatment are not particularly important as long as a lithium hydroxide solution can be produced, but examples include a carbonation and chemical conversion method using calcium hydroxide after producing lithium carbonate, a chemical conversion method using barium hydroxide, and a method using electrodialysis.

[0059] In the case of carbonation and chemical conversion methods, a lithium carbonate solution is first obtained by adding a carbonate to a lithium-containing solution or by blowing in carbon dioxide. Then, in the so-called chemical conversion method, calcium hydroxide is 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 that may remain in the solution can be removed using cation exchange resins or chelating resins.

[0060] When using barium hydroxide, a lithium hydroxide solution can be obtained by adding barium hydroxide to a lithium-containing solution and following the reaction Li2SO4 + Ba(OH)2 → 2LiOH + BaSO4. Barium that may dissolve in the solution at this time can be separated and removed using a cation exchange resin or chelating resin.

[0061] In electrodialysis, a lithium-containing solution is placed in the desalination chamber between the anion exchange membrane and the cation exchange membrane in a bipolar membrane electrodialysis machine. Pure water is then placed in the acid chamber between the bipolar membrane and the anion exchange membrane, and in the alkaline chamber between the cation exchange membrane and the bipolar membrane, and a voltage is applied between the electrodes. As a result, lithium in the metal-containing solution in the desalination chamber moves to the alkaline chamber, where the pure water is decomposed into hydroxide ions by the bipolar membrane, yielding a lithium hydroxide solution. Anions of inorganic acids such as sulfuric acid in the metal-containing solution in the desalination chamber pass through the anion exchange membrane and move to the acid chamber.

[0062] At least a portion of the lithium hydroxide solution obtained as described above can be effectively used as an alkaline pH adjuster in the metal separation process (in the embodiment shown in Figure 1, at least one process selected from the group consisting of a neutralization process, a manganese extraction process, a cobalt extraction process, and a nickel extraction process).

[0063] (Crystallization process) The lithium hydroxide solution obtained in the hydroxide step can be subjected to a crystallization step. For example, if the lithium hydroxide solution is returned to the metal separation step as a pH adjuster as described above, the lithium concentration in the solution may gradually increase due to the lithium in the newly added battery powder. Depending on the lithium concentration, a crystallization step may be performed to recover the lithium as solid lithium hydroxide.

[0064] 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. Subsequently, the lithium hydroxide can be subjected to grinding or other treatments to adjust its physical properties to the required level.

[0065] Furthermore, in the crystallization process, the post-crystallization solution is obtained as a lithium hydroxide solution in which lithium hydroxide remains without precipitation. In the metal separation process, it is possible to use the lithium hydroxide solution after the hydroxide process or the solid lithium hydroxide described above as a pH adjuster, but as shown in Figure 1, it is preferable to use the post-crystallization solution as a pH adjuster. This is because the post-crystallization solution has a concentration of lithium hydroxide close to its saturation solubility (approximately 120 g / L), and using this as a pH adjuster eliminates the need for adjustments that would be necessary when using solid lithium hydroxide, and also allows for a reduction in the amount of alkali.

[0066] (Liquid removal process) As lithium is circulated through the series of processes, and the sodium concentration in the solution reaches a certain level, sodium is mixed into the lithium hydroxide obtained in the crystallization process described above, and the quality of the lithium hydroxide decreases.

[0067] In contrast, in this embodiment, after the metal separation step, a deliquidation step is performed to remove a portion of the lithium-containing solution containing sodium obtained in the previous step, as shown in Figure 2. The remaining lithium-containing solution after a portion of it has been removed in the deliquidation step is used in a subsequent step. As a result, a portion of the sodium in the lithium-containing solution after the metal separation step is removed, thereby suppressing the increase in sodium concentration caused by the new addition of sodium-containing battery powder to the wet processing.

[0068] As a result, in the crystallization process, by adjusting the concentration ratio considering the difference in solubility between lithium and sodium, lithium hydroxide with a low sodium content can be obtained. More specifically, it is as follows: In the crystallization process, the liquid during crystallization becomes a saturated lithium hydroxide solution, and the lithium hydroxide that can no longer be dissolved precipitates as a solid. At this time, lithium is saturated in the liquid, but sodium is often not. Therefore, the more sodium that is brought into the crystallization process from sodium in the battery powder, etc., the smaller the Li / Na concentration ratio of the liquid becomes. Here, for example, if a liquid draining process is performed once when the Li / Na concentration ratio becomes small, the weight of sodium brought into the crystallization process decreases. In the crystallization process, crystallization is carried out until a certain liquid volume is reached, and as the weight of sodium brought into the process decreases, the sodium concentration in the liquid during crystallization decreases, and the Li / Na concentration ratio increases. If such a crystallized liquid with a large Li / Na concentration ratio is circulated in a series of processes as a pH adjusting agent, the weight of sodium in the circulating liquid decreases, and the sodium concentration of the lithium-containing solution after the metal separation process can be lowered. When the desaturation process is incorporated into the series of processes and performed continuously, the weight of sodium in the circulating liquid is continuously reduced, and the sodium concentration of the lithium-containing solution after the metal separation process can be maintained at a low level. As a result, lithium hydroxide with a low sodium content can be obtained in the crystallization process.

[0069] The deliquidation process may be performed periodically or irregularly when the sodium concentration of the lithium-containing solution becomes sufficiently high during the continuous operation of a series of processes as illustrated in Figure 1, or it may be incorporated into the series of processes and performed continuously. In any case, it is preferable to perform the deliquidation process so that the sodium concentration of the lithium-containing solution (more specifically, the lithium hydroxide solution used in the crystallization process, etc.) is maintained at 500 mg / L or less. More preferably, the deliquidation process can be performed so that the sodium concentration of the lithium-containing solution is maintained at 300 mg / L or less, and even more preferably at 100 mg / L or less. In this case, the lithium concentration of the lithium-containing solution used in the deliquidation process may be between 5.0 g / L and 35.0 g / L. The sodium concentration can be measured in at least one of the following processes: the acid leaching process, the neutralization process, the manganese extraction process, the cobalt extraction process, the nickel extraction process, the washing process, and the hydroxide process, preferably in each of these processes. This allows for control of the sodium concentration of the lithium-containing solution. An ICP-OES (ICP emission spectrometer) is used to measure the concentration.

[0070] Regarding the pre- and post-processing steps in Figure 2, the deliquidation step can be performed at any stage after the metal separation step, once the concentration of the metal to be separated has become sufficiently low. For example, as shown in Figure 1, when a purification step, a hydroxide step, and a crystallization step are performed after the metal separation step (nickel extraction step), the deliquidation step can be performed on the lithium-containing solution (lithium sulfate solution, etc.) between the metal separation step and the purification step, the lithium-containing solution (lithium sulfate solution, etc.) between the purification step and the hydroxide step, the lithium-containing solution (lithium hydroxide solution) between the hydroxide step and the crystallization step, and / or the lithium-containing solution (lithium hydroxide solution) after the crystallization step. If the purification step is omitted, the deliquidation step may be performed between the metal separation step and the hydroxide step.

[0071] In most cases, it is desirable to perform the deliquidation process early, as this will reduce costs because subsequent processes will involve handling lithium-containing solutions with lower sodium concentrations. However, if the deliquidation process is performed between the metal separation process and the purification process, some of the lithium-containing solution removed during the deliquidation process may contain nickel, magnesium, etc., because it has not gone through the purification process. In this case, as will be described later, in order to obtain high-quality lithium carbonate in the carbonation process for the lithium-containing solution, it is preferable to neutralize the solution before carbonation to remove nickel, magnesium, etc. It is also preferable to perform the deliquidation process after nickel, magnesium, etc. have been removed in the purification process and before the hydroxide process.

[0072] In order to actually carry out the deliquidation process, a portion of the lithium-containing solution can be extracted from containers such as storage tanks used in the predetermined processes described above, or from piping or flow paths used for transferring liquid between predetermined processes. More specifically, for example, a branching path can be provided in the piping connecting the processes, and the flow rate of the lithium-containing solution sent to and extracted on the branching path can be adjusted by valves or pipe diameter. However, the lithium-containing solution can be extracted by various specific methods, and such methods can be selected as appropriate.

[0073] (Carbonation process) Some of the lithium-containing solution extracted during the deliquidation process still contains lithium. To recover this lithium as lithium carbonate, a carbonation process can be performed on a portion of the lithium-containing solution.

[0074] In the carbonation process, lithium carbonate can be precipitated by, for example, adding a carbonate such as sodium carbonate to a portion of the lithium-containing solution, or by carbonation by blowing in carbon dioxide. From the viewpoint of preventing an increase in impurities, blowing in carbon dioxide is preferable. After adding the carbonate or blowing in carbon dioxide, the liquid temperature can be maintained for 0.5 to 2 hours, for example, by stirring as needed to a temperature within the range of 50°C to 90°C.

[0075] If the lithium-containing solution contains impurities such as nickel or magnesium due to the deliquidation process being performed between the metal separation process and the purification process, it is preferable to neutralize the solution before carbonation to remove these impurities. In neutralization, nickel, magnesium, etc., are precipitated by adding an alkali, and then separated and removed by solid-liquid separation. Any alkali can be used at this time, and lithium hydroxide solution obtained in the hydroxide process or crystallization process may also be used.

[0076] The lithium carbonate obtained as described above may be purified by washing, dissolving, decarboxylation, etc., as needed, to increase its purity.

Claims

1. A method for recovering metals from battery powder, which is a waste product of lithium-ion batteries, The process includes an acid leaching step in which lithium, sodium, and a metal to be separated from the battery powder are leached in an acidic leaching solution to obtain a metal-containing solution containing the metal, and a metal separation step in which the metal to be separated is separated from the metal-containing solution. The lithium in the lithium-containing solution obtained after the metal separation step is returned to the acid leaching step and / or the metal separation step, and the lithium is circulated within a series of steps including the acid leaching step and the metal separation step. A method for recovering metals, further comprising a deliquidation step of removing a portion of the lithium-containing solution containing sodium after the metal separation step.

2. The metal recovery method according to claim 1, further comprising a hydroxide step after the metal separation step, wherein the lithium-containing solution is subjected to a hydroxide treatment to obtain a lithium-containing solution as a lithium hydroxide solution.

3. The metal recovery method according to claim 2, wherein the liquid removal step is performed on the lithium-containing solution between the metal separation step and the hydroxide step.

4. Between the metal separation step and the hydroxide step, there is a purification step to remove impurities from the lithium-containing solution, The metal recovery method according to claim 2, wherein the liquid removal step is performed on the lithium-containing solution between the metal separation step and the purification step, and / or between the purification step and the hydroxide step.

5. The metal recovery method according to claim 2, comprising a crystallization step to obtain lithium hydroxide from the lithium-containing solution as the lithium hydroxide solution.

6. The metal recovery method according to claim 5, wherein the liquid removal step is performed on the lithium-containing solution as the lithium hydroxide solution between the hydroxide step and the crystallization step.

7. The metal recovery method according to claim 5, wherein, after the crystallization step, the dewatering step is performed on the lithium-containing solution obtained as the post-crystallization liquid in the crystallization step.

8. The above series of steps are carried out in succession. The metal recovery method according to any one of claims 1 to 7, wherein the liquid removal step is performed so that the sodium concentration of the lithium-containing solution is maintained at 500 mg / L or less.

9. A metal recovery method according to any one of claims 1 to 7, comprising a carbonation step of recovering lithium in the portion of the lithium-containing solution extracted in the liquid removal step as lithium carbonate.

10. The metal recovery method according to claim 9, wherein in the carbonation step, after neutralizing the part of the lithium-containing solution to remove impurities, lithium carbonate is precipitated by adding a carbonate or supplying carbon dioxide.

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