Metal recovery method

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 technology]

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

[0003] To recover valuable metals from lithium ion battery waste, for example, battery powder obtained through roasting of lithium ion battery waste or other predetermined dry pretreatment is subjected to wet treatment. Specifically, in the wet treatment, metals such as cobalt, nickel, manganese, lithium, aluminum, and iron in the battery powder are leached with acid to obtain a metal-containing solution in which the metals are dissolved. Next, as described in Patent Document 1, for example, aluminum, iron, and manganese, 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 is obtained in which lithium remains dissolved. The lithium-containing solution thus obtained is concentrated by repeated solvent extraction, and then carbonated by adding carbonate or blowing carbon dioxide gas into the solution, thereby recovering the lithium ions contained in the lithium-containing solution as lithium carbonate.

[0004] Regarding such metal recovery methods, Patent Documents 2 and 3 describe a method for recovering metals from lithium-ion battery waste that "reduces the use of sodium hydroxide as a pH adjuster and efficiently recovers metals from lithium-ion battery waste," which "includes a wet treatment in which metals, including lithium, in lithium-ion battery waste are leached with acid and the metal is extracted from a metal-containing solution in which the metal is dissolved, and the lithium extracted by the wet treatment is used as a pH adjuster used in the wet treatment." Patent Documents 2 and 3 also 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 solution 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 Summary of the Invention [Problem to be solved by the invention]

[0006] Incidentally, lithium-ion battery waste and the battery powder obtained therefrom may contain sodium, which is leached with acid together with metals such as lithium in the battery powder and contained in the metal-containing solution, and behaves similarly to lithium during wet processing.

[0007] Therefore, when lithium is circulated through a series of processes as described in Patent Documents 2 and 3, the concentration of not only lithium but also sodium in the solution gradually increases as the battery powder is introduced into the wet treatment. The increase in the 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 an increase in sodium concentration when lithium is circulated in a liquid through a series of steps. [Means for solving the problem]

[0009] The metal recovery method disclosed in this specification is a method for recovering metals from battery powder of lithium-ion battery waste, and includes an acid leaching step in which metals in the battery powder, including lithium, sodium, and the metal to be separated, are leached into an acid leaching solution to obtain a metal-containing solution containing the metals, and a metal separation step in which the metal to be separated is separated from the metal-containing solution, and 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, thereby circulating lithium within a series of steps including the acid leaching step and the metal separation step, and further includes a liquid removal step in which, after the metal separation step, a portion of the lithium-containing solution containing sodium is removed. [Effects of the Invention]

[0010] According to the above-described metal recovery method, it is possible to effectively suppress an increase in the sodium concentration when lithium is circulated in the liquid in a series of steps. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a flow chart showing an example of a process to which the metal recovery method of one embodiment can be applied. [Figure 2] FIG. 2 is a flow chart showing an example of a case where a liquid-removal step is performed on the lithium-containing solution in the process of FIG. 1 according to one embodiment of the metal recovery method. [Figure 3] FIG. 1 is a flow chart showing an example of each step for obtaining battery powder from lithium ion battery waste. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the above-mentioned metal recovery method will be described in detail. One embodiment of the metal recovery method is a method for recovering metals from battery powder of lithium-ion battery waste. This method includes an acid leaching step of leaching metals, including lithium and a target metal in the battery powder, into an acidic leaching solution to obtain a metal-containing solution containing the metals as metal ions, and a metal separation step of separating the target metal from the metal-containing solution.

[0013] Here, as illustrated in FIG. 1, 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 a lithium sulfate solution, a lithium hydroxide solution, or the like, thereby circulating lithium within a series of steps including the acid leaching step and the metal separation step. The lithium hydroxide solution can be used as a pH adjuster, etc., in the metal separation step. By circulating lithium, it becomes possible to maintain a high lithium concentration in the solution throughout the series of steps, and in some cases, the lithium hydroxide solution can be used as all the pH adjuster required in the metal separation step. Lithium hydroxide may be recovered from any remaining lithium hydroxide solution.

[0014] Incidentally, battery powders may contain sodium. This sodium is leached in the acid leaching process and contained in the metal-containing solution, and is not separated together with lithium in the metal separation process but is contained in the subsequent lithium-containing solution. In this case, as described above, if the lithium in the lithium-containing solution is returned to the acid leaching process or the metal separation process to circulate the lithium, not only the lithium concentration but also the sodium concentration in the solution increases over the series of processes. Sodium contained at a high concentration in the solution may be mixed into lithium hydroxide obtained in, for example, the crystallization process, thereby reducing its quality.

[0015] To address this issue, in this embodiment, a liquid-removal step is performed after the metal separation step, in which a portion of the lithium-containing solution containing sodium is removed, as shown in FIG. 2. The remaining lithium-containing solution after removing a portion of the lithium-containing solution in the liquid-removal step is returned to the series of steps and used to recycle lithium. By performing the liquid-removal step, a portion of the sodium in the lithium-containing solution after the metal separation step is removed, thereby making it possible to suppress an increase in the sodium concentration. As a result, it is possible to effectively suppress a decrease in the quality of the lithium hydroxide produced in the crystallization step.

[0016] In the example shown in Figure 1, the metal separation step is followed by a solution purification step, a hydroxide step, and a crystallization step, which are performed in this order, 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 may be omitted, or another step may be added. Furthermore, battery powder may be obtained by subjecting lithium-ion battery waste to pretreatment steps such as roasting, crushing, and sieving, as exemplified in Figure 3. Here, the description will be made with reference to Figures 1 to 3, but Figures 1 to 3 are merely examples and are not limited to such specific flows.

[0017] (Lithium-ion battery waste) The target lithium-ion battery waste is lithium-ion secondary batteries that can be used in mobile phones and various other electronic devices, etc., that have been discarded due to the end of the battery product's life, manufacturing defects, or other reasons. Recovering valuable metals from such lithium-ion battery waste is desirable from the perspective of effective resource utilization. Lithium-ion battery waste refers to lithium-ion batteries that are eligible for recycling, regardless of whether they are traded for a value, free of charge, or treated as industrial waste.

[0018] Lithium-ion battery waste has an aluminum-containing casing as an exterior that encases the battery. This casing may be made of aluminum alone, aluminum and iron, or aluminum laminate. Lithium-ion battery waste may also contain a cathode active material, such as a single metal oxide containing lithium and one or more selected from the group consisting of nickel, cobalt, and manganese, or a composite metal oxide containing two or more selected metals. The cathode active material may also be coated and fixed to an aluminum foil (cathode substrate) with an organic binder such as polyvinylidene fluoride (PVDF). Lithium-ion battery waste may also contain copper, iron, etc. Furthermore, the casing of lithium-ion battery waste typically contains an electrolyte solution, in which an electrolyte such as lithium hexafluorophosphate is dissolved in an organic solvent. Examples of organic solvents that may be used include ethylene carbonate and diethyl carbonate.

[0019] (Pretreatment process) Lithium-ion battery waste is often subjected to a pretreatment process as a dry process. The pretreatment process may include at least one of roasting, crushing, and sieving. Lithium-ion battery waste is converted into battery powder through the pretreatment process. The roasting, crushing, and sieving pretreatment processes may be performed individually as needed, or may be performed in any order. Battery powder refers to a powder obtained by separating and concentrating positive electrode material components from lithium-ion battery waste through some kind of pretreatment. Battery powder may also be obtained by crushing and sieving lithium-ion battery waste with or without heat treatment, resulting in a powder with concentrated positive electrode material components.

[0020] In roasting, the lithium-ion battery waste is heated. Roasting can convert metals such as lithium and cobalt contained in the lithium-ion battery waste into a more soluble form. During roasting, the lithium-ion battery waste is preferably heated at a temperature ranging from 450°C to 1000°C, preferably from 600°C to 800°C, for example, for 0.5 to 4 hours. In roasting, either heating in an air atmosphere or heating in an inert atmosphere such as nitrogen can be performed. Alternatively, both heating in an air atmosphere and heating in an inert atmosphere can be performed in this order or in the reverse order. The roasting furnace may be a batch or continuous furnace. For example, a stationary furnace is used for the batch furnace, and a rotary kiln is used for the continuous furnace. Various other furnaces can also be used.

[0021] During roasting, at least a portion of the electrolyte is removed from the lithium-ion battery waste by evaporation of the electrolyte, etc. In many cases, when lithium-ion battery waste is heated during roasting, the components of the internal electrolyte evaporate sequentially, starting with those with low boiling points. When roasting is performed, the electrolyte is removed and rendered harmless, and the organic binder is decomposed, facilitating separation of the aluminum foil and the positive electrode active material during crushing and sieving, as described below. Note that although the composition of the positive electrode active material changes upon roasting, the positive electrode active material will be referred to here even if it has undergone roasting.

[0022] After roasting, the lithium-ion battery waste can be crushed to remove the positive electrode active material and other materials from the casings. In the crushing, the casings of the lithium-ion battery waste are destroyed and the positive electrode active material is selectively separated from the aluminum foil on which the positive electrode active material is applied.

[0023] For crushing, various known devices or equipment can be used, but it is particularly preferable to use an impact crusher that can crush lithium-ion battery waste by applying impact while cutting the waste. Examples of this impact crusher include a sample mill, hammer mill, pin mill, wing mill, tornado mill, and hammer crusher. A screen can be installed at the outlet of the crusher, and the lithium-ion battery waste is discharged from the crusher through the screen once it has been crushed to a size that can pass through the screen.

[0024] After crushing the lithium-ion battery waste, it is sieved using a sieve with appropriate openings, whereby aluminum and copper remain on the sieve and battery powder from which aluminum and copper have been removed to some extent is obtained below the sieve.

[0025] The battery powder obtained in the pretreatment step contains nickel, cobalt, lithium, manganese, etc. For example, the battery powder may contain, but is not limited to, 1% to 30% by mass of nickel, 1% to 30% by mass of cobalt, 2% to 8% by mass of lithium, and 1% to 30% by mass of manganese. The battery powder may further contain 1% to 10% by mass of aluminum, 1% to 5% by mass of iron, 1% to 10% by mass of copper, and 0.001% to 0.1% by mass of sodium. This embodiment targets battery powder containing lithium, sodium, and a metal to be separated. 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 step, the metals in the battery powder are leached with an acidic leaching solution such as sulfuric acid. This results in a solution in which the metals in the battery powder are dissolved and a leaching residue that remains undissolved. Here, the solution in which the metals in the battery powder are dissolved in each step from the end of the acid leaching step to the nickel extraction step described below is also referred to as a metal-containing solution.

[0027] In the acid leaching step, the pH of the acid leachate and post-leaching solution may be less than 3.5. The oxidation-reduction potential (ORP value, based on silver / silver chloride potential) may be 100 mV or less. After the completion of leaching, solid-liquid separation may be performed to separate the leaching residue from the metal-containing solution. However, the metal-containing solution containing the leaching residue may be subjected to the subsequent neutralization step without solid-liquid separation. As described below, the post-extraction solution from the nickel extraction step (such as a lithium sulfate solution) or water may be used as a diluent to adjust the pH of the acid leachate. This allows lithium to circulate throughout the series of steps in the wet treatment, allowing lithium in the solution to be concentrated during the process.

[0028] The metal-containing solution obtained in the acid leaching step may have, for example, a nickel concentration of 10 g / L to 50 g / L, a cobalt concentration of 5 g / L to 50 g / L, a lithium concentration of 2 g / L to 10 g / L, a manganese concentration of 0 g / L to 50 g / L, an aluminum concentration of 1.0 g / L to 20 g / L, an iron concentration of 0.1 g / L to 5.0 g / L, a copper concentration of 0.005 g / L to 0.2 g / L, and a sodium concentration of 0.001 g / L to 0.1 g / L.

[0029] (neutralization process) If the metal-containing solution obtained in the acid leaching step contains aluminum and / or iron, a neutralization step can be carried out at the beginning of the metal separation step, in which the pH of the metal-containing solution is increased and the neutralization residue is separated to obtain a neutralized solution. The neutralization step can include a dealumination step and a de-ironization step. However, if the metal-containing solution does not contain aluminum and / or iron, the dealumination step and / or the de-ironization step may be omitted.

[0030] In the dealumination step, the pH of the metal-containing solution is increased to precipitate at least a portion of the aluminum, which is then removed by solid-liquid separation. At this time, for example, by increasing the pH to within a range of 4.0 to 5.0 using a pH adjuster at a liquid temperature of 50 to 90°C, aluminum can be effectively separated while suppressing the precipitation of nickel and / or cobalt.

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

[0032] Examples of pH adjusters used for neutralization in the above-mentioned dealumination step, iron removal step, etc. include solid or liquid lithium hydroxide, sodium hydroxide, sodium carbonate, ammonia, etc., of which lithium hydroxide is preferred because it can prevent sodium and other substances from being mixed into the lithium hydroxide recovered in the crystallization step described below. The lithium hydroxide solution obtained in the hydroxide step or the post-crystallization liquid (lithium hydroxide solution) obtained in the crystallization step can be used as the pH adjuster, thereby circulating lithium within the series of steps.

[0033] (Manganese extraction process) The metal-containing solution may be subjected to the neutralization step as necessary, and then the manganese may be extracted and removed by solvent extraction. In this case, if aluminum remains in the metal-containing solution, not only manganese but also aluminum is 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 phosphoric acid (abbreviation: D2EHPA, e.g., trade name: DP8R). Alternatively, the extractant may be a mixture of a phosphate ester extractant and an oxime extractant. In this case, the oxime extractant is preferably an aldoxime or one containing aldoxime as the main component. Specific examples include 2-hydroxy-5-nonylacetophenone oxime (trade name: LIX84), 5-dodecylsalicyaldoxime (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 organic solvent such as an aromatic, paraffinic, or naphthenic solvent to a concentration of 10% by volume to 30% by volume, and this may be used as the solvent.

[0036] During extraction, the equilibrium pH is preferably adjusted to 2.3 to 3.5, more preferably 2.5 to 3.0. The pH adjuster used at this time is preferably a lithium hydroxide solution, and for example, the lithium hydroxide solution obtained in the hydroxide step or crystallization step described below can be used.

[0037] As an example of extraction, more specifically, the solution (aqueous phase) and the solvent (organic phase) are brought into contact and stirred and mixed, typically in a mixer, for 5 to 60 minutes to react the metal with the extractant. The temperature during extraction is from room temperature (approximately 15 to 25°C) to 60°C or less, and is preferably carried out at 35 to 45°C for reasons of extraction speed, phase separation, and evaporation of the organic solvent. The mixed organic and aqueous phases are then separated in a settler due to the difference in specific gravity. Extractions in processes other than the manganese extraction process can also be carried out in substantially the same manner.

[0038] During extraction, it is desirable to perform countercurrent multistage extraction, in which the aqueous phase and solvent flow in opposite directions for each extraction. This can increase the extraction rate of manganese while suppressing the extraction of cobalt, nickel, and lithium. When using countercurrent multistage extraction, it is effective to set the equilibrium pH during the first extraction stage within the above-mentioned range and then lower the equilibrium pH with each subsequent extraction stage.

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

[0040] (Cobalt extraction process and crystallization process) After manganese has been extracted, 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 phosphoric acid extractant, especially a phosphonate extractant. 2-Ethylhexyl 2-ethylhexyl phosphonate (trade names: PC-88A, Ionquest 801) is particularly suitable from the viewpoint of the separation efficiency of nickel and cobalt. The extractant can be diluted with a hydrocarbon organic solvent to a concentration of 10% to 30% by volume and used as a solvent.

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

[0043] Cobalt extraction is also preferably performed by countercurrent multistage extraction, in which the aqueous phase and the solvent flow in opposite directions in each extraction, which can increase the cobalt extraction rate while suppressing the extraction of nickel and lithium.

[0044] During the extraction, not only cobalt but also small amounts of nickel and lithium may be extracted into the solvent. In this case, if necessary, the solvent from which cobalt has been extracted may be subjected to one or more scrubbing steps using a scrubbing solution to remove nickel and lithium that may be contained in the solvent. The scrubbing solution may be, for example, a sulfuric acid solution with a pH of 3.5 to 5.5. The post-scrubbing solution may contain nickel 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 step and use this as the pre-extraction solution for the cobalt extraction step. This allows nickel and lithium to be circulated or retained within the series of steps without loss. However, if the solvent from which cobalt has been extracted does not contain nickel or lithium, scrubbing may not be necessary.

[0045] The stripping is then carried out using a solvent containing cobalt. The stripping solution used for the stripping may be any inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid, but sulfuric acid is preferred if sulfate is to be obtained in the subsequent crystallization step. The stripping is carried out under pH conditions such that as much of the cobalt as possible is transferred from the solvent to the stripping solution. Specifically, the pH is preferably in the range of 2.0 to 4.0, and even more preferably in the range of 2.5 to 3.5.

[0046] The strip-extracted solution can be subjected to a crystallization process. In the crystallization process, the strip-extracted solution is heated, for example, to 40°C to 120°C and concentrated. This process crystallizes cobalt, yielding a cobalt salt such as cobalt sulfate. The cobalt salt thus obtained preferably has a nickel content of 5 mass ppm or less, and nickel has been sufficiently removed, making it effective as a raw material for the production of lithium-ion secondary batteries and other batteries. The crystallization solution may contain uncrystallized cobalt and lithium. Therefore, it is desirable to mix the crystallization solution with the strip-extracted solution before the crystallization process and subject it to another crystallization process, use it to adjust the cobalt concentration of the scrubbing solution used as the solvent for cobalt extraction, or mix it with the metal-containing solution after the manganese extraction process and subject it to the cobalt extraction process. In this way, cobalt and lithium can be circulated or retained within the series of processes and concentrated without loss.

[0047] (Nickel extraction process and crystallization process) The metal-containing solution after cobalt extraction in the cobalt extraction step mainly contains nickel and lithium. In order to recover nickel from this metal-containing solution, nickel can be extracted from the metal-containing solution into a solvent by a solvent extraction method.

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

[0049] The solvent used in the nickel extraction step preferably contains a carboxylic acid extractant. Examples of carboxylic acid extractants include neodecanoic acid and naphthenic acid, with neodecanoic acid (such as Versatic Acid 10 (VA-10) manufactured by Shell Chemical Industries, Ltd.) being preferred due to its ability to extract nickel. The extractant may be diluted with a hydrocarbon organic solvent such as an aromatic, paraffinic, or naphthenic solvent 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 preferably used as a pH adjuster for adjusting the pH at this time, and for example, the lithium hydroxide solution obtained in the hydroxide step or crystallization step described below can be used.

[0051] It is desirable to carry out the extraction in multiple stages using a countercurrent system, in which the metal-containing solution and the solvent flow in opposite directions. This suppresses the extraction of lithium into the solvent, thereby increasing the extraction rate of nickel. When using multiple countercurrent extraction stages, it is effective to set the equilibrium pH during the first extraction stage within the above range and then lower the equilibrium pH during each stage.

[0052] If necessary, the solvent that has become nickel-containing after extraction may be subjected to one or more scrubbing steps using a scrubbing solution to remove lithium that may be contained in the solvent. The scrubbing solution may be, for example, a sulfuric acid solution with a pH of 5.0 to 6.0. The post-scrubbing solution may contain lithium. Therefore, it is desirable to mix a part or all of the post-scrubbing solution with the metal-containing solution obtained after the cobalt extraction step, and use this as the pre-extraction solution for the nickel extraction step. This allows lithium to be circulated or retained within the series of steps and concentrated without loss. However, if the nickel-containing solvent does not contain lithium, scrubbing may not be necessary.

[0053] The stripping is then carried out using a solvent containing nickel. The stripping solution used for the stripping may be any inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid, but sulfuric acid is preferred if sulfate is to be obtained in the subsequent crystallization step. The pH is preferably in the range of 1.0 to 3.0, more preferably 1.5 to 2.5. The O / A ratio and 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 stripping solution such as a nickel sulfate solution is obtained by stripping, it can be electrolyzed and dissolved as needed, and then heated to 40°C to 120°C in a crystallization process to crystallize the nickel into nickel salts such as nickel sulfate. This produces nickel salts. The crystallization solution may contain uncrystallized nickel and lithium. Therefore, it is desirable to mix the crystallization solution with the stripping solution before the crystallization process and subject it to another crystallization process, use it to adjust the nickel concentration of the scrubbing solution for the nickel-containing solvent, or mix it with the metal-containing solution after the cobalt extraction process and subject it to the nickel extraction process. This allows nickel and lithium to be concentrated by circulating or retaining them within the series of processes without loss.

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

[0056] (liquid purification process) The lithium-containing solution (lithium sulfate solution, etc.) that is the post-extraction solution in the nickel extraction step may contain trace amounts of cations such as nickel and magnesium that were not completely separated in the metal separation step. Nickel and magnesium are cations like lithium, and they behave similarly to lithium during electrodialysis in the hydroxide step described below, making them difficult to separate from lithium. Furthermore, when electrodialysis is performed on a metal-containing solution containing nickel and magnesium, nickel hydroxides and magnesium hydroxides are generated in the resulting lithium hydroxide solution, which may cause process problems and make it impossible to continue the electrodialysis.

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

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

[0059] In the carbonation and chemical conversion method, a lithium carbonate solution is first obtained by adding carbonate or blowing carbon dioxide into a lithium-containing solution. Then, in the so-called chemical conversion method, calcium hydroxide is added to the lithium carbonate solution to produce a lithium hydroxide solution according to the reaction formula Li2CO3 + Ca(OH)2 → 2LiOH + CaCO3. Calcium that may remain in the solution can be removed using a cation exchange resin or a chelating resin.

[0060] When barium hydroxide is used, it is added to a lithium-containing solution to obtain a lithium hydroxide solution based on the reaction Li2SO4 + Ba(OH)2 → 2LiOH + BaSO4. Note that 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 bipolar membrane electrodialysis device is used. A lithium-containing solution is placed in the deionization compartment between the anion exchange membrane and the cation exchange membrane. Pure water is placed in the acid compartment between the bipolar membrane and the anion exchange membrane, and in the alkaline compartment between the cation exchange membrane and the bipolar membrane. A voltage is then applied between the electrodes. Lithium in the metal-containing solution in the deionization compartment moves to the alkaline compartment, where the bipolar membrane decomposes the pure water into hydroxide ions, producing a lithium hydroxide solution. Anions of inorganic acids, such as sulfuric acid, in the metal-containing solution in the deionization compartment pass through the anion exchange membrane and move to the acid compartment.

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

[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 lithium as solid lithium hydroxide.

[0064] In the crystallization step, a crystallization procedure such as thermal concentration or vacuum distillation can be performed to precipitate lithium hydroxide. In the case of thermal concentration, a higher temperature during crystallization is preferable because the process proceeds more quickly. However, after crystallization, the temperature during drying of the crystallized product is preferably less than 60°C, at which water of crystallization does not detach. This is because anhydrous lithium hydroxide from which water of crystallization has been detached is deliquescent and therefore difficult to handle. Thereafter, a pulverization process or the like can be performed to adjust the lithium hydroxide to the required physical properties.

[0065] In the crystallization step, the post-crystallization liquid is obtained as a lithium hydroxide solution in which lithium hydroxide remains without being precipitated. In the metal separation step, the lithium hydroxide solution after the hydroxide oxidation step or the solid lithium hydroxide described above can be adjusted and used as a pH adjuster, but it is preferable to use the post-crystallization liquid as a pH adjuster, as shown in Figure 1. The post-crystallization liquid has a concentration of lithium hydroxide close to the saturated solubility (approximately 120 g / L), and using this as a pH adjuster eliminates the adjustment required when using solid lithium hydroxide and also allows the amount of alkali to be reduced.

[0066] (liquid removal process) When lithium is circulated through a series of steps and the sodium concentration in the liquid becomes high to a certain extent, sodium is mixed into the lithium hydroxide obtained in the crystallization step, and the quality of the lithium hydroxide decreases.

[0067] In contrast, in this embodiment, after the metal separation step, a liquid removal step is performed in which a part of the lithium-containing solution containing sodium obtained in the previous step is removed, as shown in Fig. 2. The remaining lithium-containing solution remaining after the part of the lithium-containing solution is removed in the liquid removal step is subjected to a subsequent step. This removes a part of the sodium in the lithium-containing solution after the metal separation step, thereby suppressing an increase in the sodium concentration caused by newly adding battery powder containing sodium to the wet treatment.

[0068] Therefore, in the crystallization process, lithium hydroxide with a low sodium content can be obtained by adjusting the concentration ratio taking into account the difference in the solubility of lithium and sodium. More specifically, this is as follows: During the crystallization process, the liquid becomes a saturated solution of lithium hydroxide, and the lithium hydroxide that cannot be dissolved precipitates as a solid. At this time, lithium is saturated in the liquid, but sodium is often not saturated. Therefore, the Li / Na concentration ratio of the liquid decreases as the weight of sodium introduced into the crystallization process increases. For example, if a liquid-removal process is performed once when the Li / Na concentration ratio decreases, the weight of sodium introduced into the crystallization process decreases. In the crystallization process, crystallization is performed until a certain liquid volume is reached. If the weight of sodium introduced decreases, the sodium concentration in the liquid during crystallization decreases, and the Li / Na concentration ratio increases. If such a post-crystallization liquid with a high Li / Na concentration ratio is circulated as a pH adjuster through a series of processes, the weight of sodium in the circulating liquid decreases, thereby lowering the sodium concentration of the lithium-containing solution after the metal separation process. When the liquid removal step is incorporated into a series of steps and is 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 step can be maintained low. As a result, lithium hydroxide with a low sodium content can be obtained in the crystallization step.

[0069] The liquid-removal step may be performed periodically or irregularly when the sodium concentration of the lithium-containing solution becomes high to a certain extent during the continuous operation of the series of steps as illustrated in FIG. 1 , or may be performed continuously as part of the series of steps. In either case, the liquid-removal step is preferably performed so that the sodium concentration of the lithium-containing solution (more specifically, the lithium hydroxide solution to be subjected to the crystallization step, etc.) is maintained at 500 mg / L or less. More preferably, the liquid-removal step can be performed so that the sodium concentration of the lithium-containing solution is maintained at 300 mg / L or less, and even 100 mg / L or less. In this case, the lithium concentration of the lithium-containing solution to be subjected to the liquid-removal step may be 5.0 g / L to 35.0 g / L. The sodium concentration can be measured in at least one of the acid leaching step, neutralization step, manganese extraction step, cobalt extraction step, nickel extraction step, washing step, and hydroxide step, preferably in each of these steps. This allows the sodium concentration of the lithium-containing solution to be controlled. Furthermore, the concentration is measured using an ICP-OES (inductively coupled plasma (ICP) optical emission spectrometer).

[0070] With respect to the upstream and downstream processes in Figure 2, the liquid-removal process can be performed at any stage after the metal separation process, as long as the concentration of the metal to be separated is sufficiently low. For example, as shown in Figure 1, when a liquid purification process, a hydroxide process, and a crystallization process are performed after the metal separation process (nickel extraction process), the liquid-removal process can be performed on the lithium-containing solution (lithium sulfate solution, etc.) between the metal separation process and the liquid purification process, the lithium-containing solution (lithium sulfate solution, etc.) between the liquid purification process and the hydroxide process, the lithium-containing solution (lithium hydroxide solution) between the hydroxide process and the crystallization process, and / or the lithium-containing solution (lithium hydroxide solution) after the crystallization process. If the liquid purification process is omitted, the liquid-removal process may be performed between the metal separation process and the hydroxide process.

[0071] In many cases, it is desirable to perform the liquid-removal step at an early stage from the viewpoint of reducing costs, since the subsequent steps will involve handling a lithium-containing solution with a low sodium concentration. However, if the liquid-removal step is performed between the metal separation step and the liquid purification step, nickel, magnesium, etc. may be contained in a portion of the lithium-containing solution removed in the liquid-removal step because the solution has not been subjected to the liquid purification step. In this case, as will be described later, in order to obtain high-quality lithium carbonate in the carbonation step of the portion of the lithium-containing solution, it is preferable to remove nickel, magnesium, etc. by neutralizing the solution before carbonation. Furthermore, it is preferable to perform the liquid-removal step after nickel, magnesium, etc. have been removed in the liquid purification step and before the hydroxide step.

[0072] In addition, when actually performing the liquid-removing step, a portion of the lithium-containing solution can be removed from a container such as a storage tank used in the above-described predetermined step, or from a pipe or a flow path used for transferring the solution between the predetermined steps. More specifically, for example, a branch path can be provided in a pipe connecting the steps, and the flow rate of the lithium-containing solution sent to the branch path and removed can be adjusted by a valve or the diameter of the pipe. However, the present invention is not limited to these, and the lithium-containing solution can be removed by various specific methods, and such methods can be selected as appropriate.

[0073] (carbonation process) The part of the lithium-containing solution extracted in the liquid-removal step contains lithium. In order to recover this lithium as lithium carbonate, the part of the lithium-containing solution can be subjected to a carbonation step.

[0074] In the carbonation step, lithium carbonate can be precipitated by adding a carbonate such as sodium carbonate to a part of the lithium-containing solution or by blowing in carbon dioxide gas. From the viewpoint of preventing an increase in impurities, blowing in carbon dioxide gas is preferred. After adding the carbonate or blowing in the carbon dioxide gas, the liquid temperature can be set to a range of 50°C to 90°C, and the solution can be stirred as needed and maintained at this temperature for 0.5 to 2 hours.

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

[0076] The lithium carbonate obtained as described above may be purified, as needed, by washing, dissolution, decarbonation, or the like, in order to increase its purity.

Claims

1. A method for recovering metals from battery powder of lithium ion battery waste, comprising: the method includes an acid leaching step of leaching metals, including lithium, sodium, and a metal to be separated, in the battery powder into an acid leaching solution to obtain a metal-containing solution containing the metals; and 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, thereby circulating lithium within a series of steps including the acid leaching step and the metal separation step; The metal recovery method further comprises, after the metal separation step, a liquid removal step of removing a portion of the lithium-containing solution containing sodium.

2. 2. The metal recovery method according to claim 1, further comprising a hydroxylation step of subjecting the lithium-containing solution to a hydroxylation treatment after the metal separation step 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. a solution purification step for removing impurities in the lithium-containing solution between the metal separation step and the hydroxide step, 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 solution purification step and / or between the solution purification step and the hydroxide step.

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

6. 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 the liquid-removal step is performed on the lithium-containing solution as the post-crystallization liquid obtained in the crystallization step after the crystallization step.

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

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

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

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