Impurity removal method and metal recovery method

Abstract

Provided are an impurity removal method capable of effectively removing impurities such as fluoride ions and a metal recovery method. A method for removing impurities from a metal-containing solution obtained by leaching battery powder of a lithium-ion battery waste with an acid, the method comprising: a metal separation step of separating other metal ions from the metal-containing solution containing lithium ions and other metal ions; and after the metal separation step, performing electrodialysis using a bipolar membrane on the metal-containing solution containing fluoride ions as an impurity to obtain a lithium hydroxide solution and an acidic solution, wherein the lithium hydroxide solution is used as a pH adjuster in the metal separation step.

Description

Technical Field

[0001] This specification discloses an impurity removal method and a metal recovery method.

Background Art

[0002] In recent years, from the perspective of effective utilization of resources, extensive studies have been conducted on recovering valuable metals such as cobalt and nickel contained in lithium-ion battery waste discarded due to product life or manufacturing defects or other reasons.

[0003] The process for recovering valuable metals from lithium-ion battery waste may include, for example, roasting of lithium-ion battery waste and other predetermined dry treatments, and wet treatment of the battery powder obtained after the dry treatment.

[0004] In the 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. Then, as described in Patent Document 1, for example, aluminum ions, iron ions, manganese ions, etc. are sequentially or simultaneously removed from the metal-containing solution by neutralization or solvent extraction. Thereafter, cobalt ions and nickel ions in the metal-containing solution are separated by solvent extraction. After nickel ions are separated by extraction, a metal-containing solution in which lithium ions remain is obtained.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Incidentally, for the neutralization and solvent extraction described above, a pH adjuster for increasing and adjusting the pH is used. As this pH adjuster, it is possible to separately prepare and use sodium hydroxide or the like, but it is desirable to use a lithium hydroxide solution prepared from the above-mentioned metal-containing solution obtained after solvent extraction of cobalt ions and / or nickel ions and other metals. Thereby, it is possible to suppress the mixing of sodium or the like derived from the separately prepared pH adjuster, and it is possible to reduce the cost of the pH adjuster.

[0007] However, the metal-containing solution contains impurities such as fluoride ions. When such a metal-containing solution is used as a lithium hydroxide solution and circulated in a metal recovery process using it as a pH adjuster, there is a concern that the above impurities will accumulate and concentrate, affecting the process.

[0008] This specification provides an impurity removal method capable of effectively removing impurities such as fluoride ions and a metal recovery method.

Means for Solving the Problems

[0009] The impurity removal method disclosed in this specification is a method for removing impurities from a metal-containing solution obtained by leaching battery powder of lithium-ion battery waste with an acid, and includes a metal separation step of separating the other metal ions from the metal-containing solution containing lithium ions and other metal ions, and after the metal separation step, performing electrodialysis using a bipolar membrane on the metal-containing solution containing lithium ions and fluoride ions of impurities to obtain a lithium hydroxide solution and an acidic solution. The lithium hydroxide solution is used as a pH adjuster in the metal separation step.

[0010] Also, the metal recovery method disclosed in this specification is a method for recovering metals from battery powder of lithium-ion battery waste, which uses the above impurity removal method.

Advantages of the Invention

[0011] According to the above-described impurity removal method, impurities such as fluoride ions can be effectively removed.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0013] Hereinafter, embodiments of the above-described impurity removal method and metal recovery method will be described in detail. The impurity removal method of one embodiment is a method for removing impurities from a metal-containing solution obtained by leaching battery powder of lithium-ion battery waste with an acid. This method includes a metal separation step of separating other metal ions from a metal-containing solution containing lithium ions and other metal ions, and after separating the other metal ions in the metal separation step, performing electrodialysis using a bipolar membrane on the metal-containing solution containing lithium ions and fluoride ions of impurities to obtain a lithium hydroxide solution and an acidic solution. The lithium hydroxide solution obtained in the electrodialysis step is used as a pH adjuster in the metal separation step.

[0014] When electrodialysis is performed in the electrodialysis step, most of the fluoride ions contained in the metal-containing solution migrate to the acidic solution and are almost removed from the lithium hydroxide solution, effectively removed. As a result, when the lithium hydroxide solution is used as a pH adjuster in the metal separation step and circulated within the wet treatment of the metal recovery method, the accumulation and concentration of fluoride ions can be suppressed. Also, anions of inorganic acids such as sulfate ions, nitrate ions, and chloride ions also migrate to the acidic solution and are almost not contained in the lithium hydroxide solution, so a highly pure lithium hydroxide solution can be obtained. This greatly contributes to the improvement of the quality of lithium hydroxide.

[0015] In the metal recovery method of the embodiment described here, as illustrated in FIG. 1, as the wet treatment, an acid leaching step of leaching the battery powder of the lithium ion battery waste with an acid to obtain a metal-containing solution, and the above metal separation step and electrodialysis step are performed. The lithium hydroxide solution obtained in the electrodialysis step is concentrated as necessary and then used as a pH adjuster in the metal separation step. In FIG. 1, the metal separation step includes neutralization, solvent extraction of manganese ions and / or aluminum ions (extraction of Mn etc.), solvent extraction of cobalt ions, and solvent extraction of nickel ions. However, depending on the types of metal ions other than lithium ions contained in the metal-containing solution, at least one of neutralization and multiple solvent extractions may be omitted.

[0016] (Lithium ion battery waste) The lithium ion battery waste targeted is a lithium ion secondary battery that can be used in mobile phones and various other electronic devices, etc., and is discarded due to the life of the battery product, manufacturing defects, or other reasons. Recovering valuable metals from such lithium ion battery waste is preferable from the viewpoint of effective utilization of resources.

[0017] The lithium ion battery waste has a housing containing aluminum as an exterior that wraps around the lithium ion secondary battery. Examples of this housing include those made of only aluminum, those containing aluminum and iron, aluminum laminate, etc.

[0018] In addition, lithium-ion battery waste may contain, within the above-mentioned housing, a single metal oxide containing lithium and one type selected from the group consisting of nickel, cobalt, and manganese, or a cathode active material composed of a composite metal oxide containing two or more types thereof, etc. The cathode active material may be, for example, an aluminum foil (cathode substrate) coated and fixed with polyvinylidene fluoride (PVDF) or other organic binders. In addition, copper, iron, etc. may be contained in the lithium-ion battery waste.

[0019] Furthermore, 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. As the organic solvent, for example, ethylene carbonate, diethyl carbonate, etc. may be used.

[0020] (Pretreatment process) In many cases, a pretreatment process of dry treatment is performed on the lithium-ion battery waste. The pretreatment process may include at least one of roasting, crushing, and sieving. The lithium-ion battery waste becomes battery powder through the pretreatment process. The roasting, crushing, and sieving in the pretreatment process may be performed respectively as necessary and may be performed in any order. In the example shown in Figure 2, roasting, crushing, and sieving are performed in this order.

[0021] Note that the battery powder means powder in which the cathode material component is separated and concentrated by subjecting the lithium-ion battery waste to some treatment. The battery powder may be obtained as a powdery material in which the cathode material component is concentrated by performing crushing and sieving on the lithium-ion battery waste with or without heat treatment.

[0022] 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, and more preferably 600°C to 800°C, for 0.5 hours to 4 hours. Roasting can be performed in an air atmosphere or an inert atmosphere such as nitrogen, or both the air atmosphere and the inert atmosphere may be performed in this 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.

[0023] 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. Also, when the lithium-ion battery waste reaches a higher temperature, resins such as organic binders decompose or vaporize. Even if a part of the electrolyte or the organic binder is removed in this way, predetermined components such as fluorine contained in the electrolyte or the organic binder may remain and be contained in the battery powder obtained after the pretreatment process. When roasting is performed, the electrolyte is removed and rendered harmless, and the organic binder is decomposed, which promotes the separation of the aluminum foil and the positive electrode active material during the subsequent crushing and sieving. Note that although the composition of the positive electrode active material changes due to roasting, here it will be called the positive electrode active material even if it has undergone roasting.

[0024] After roasting, crushing can be performed to take out 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 broken, and the positive electrode active material is selectively separated from the aluminum foil coated with the positive electrode active material.

[0025] For crushing, various known apparatuses or devices can be used. In particular, it is preferable to use an impact crusher that can apply an impact while cutting lithium-ion battery waste to crush it. Examples of such impact crushers include sample mills, hammer mills, pin mills, wing mills, tornado mills, hammer crushers, etc. A screen can be installed at the outlet of the crusher, whereby the lithium-ion battery waste is discharged through the screen from the crusher when it is crushed to a size that can pass through the screen.

[0026] After crushing the lithium-ion battery waste, screening is performed using a sieve with an appropriate mesh size. Thereby, aluminum and copper remain on the sieve, and battery powder with aluminum and copper removed to a certain extent can be obtained under the sieve.

[0027] The battery powder obtained in the pretreatment step contains lithium and at least one other metal selected from the group consisting of cobalt, nickel, manganese, aluminum, iron, and copper in addition to lithium. Typically, the battery powder contains lithium and at least one of nickel and cobalt. For example, the lithium content of the battery powder is 2% to 8% by mass, the cobalt content is 1% to 30% by mass, the nickel content is 1% to 30% by mass, the manganese content is 1% to 30% by mass, the aluminum content is 1% to 10% by mass, the iron content is 1% to 5% by mass, and the copper content is 1% to 10% by mass. Also, the battery powder may contain fluorine at 0.1% to 10% by mass.

[0028] The battery powder can be contacted with water before the acid leaching process described later in order to extract substantially only lithium therefrom. Thereby, lithium in the battery powder leaches into the water. In this case, the battery powder as the water leaching residue is subjected to the acid leaching process. However, when performing water leaching, the equipment is required, and the processing time increases by performing both the water leaching and the acid leaching in the acid leaching process of the acid leaching step. In addition, it may be necessary to control conditions such as roasting for effectively leaching lithium with water. Also, even if managed in this way, the leaching rate of lithium by water may not be increased so much. Therefore, the battery powder obtained as described above may be subjected to acid leaching in the acid leaching process without performing water leaching. When water leaching is not performed, it becomes easier to maintain a high lithium ion concentration in the liquid in the wet treatment after the acid leaching process.

[0029] (Acid Leaching Process) In the acid leaching process, the above-mentioned battery powder is added to an acidic leaching solution of sulfuric acid, nitric acid, hydrochloric acid or other inorganic acids, etc., to leach lithium and other metals contained in the lithium ion battery waste with an acid.

[0030] The acid leaching process can be carried out by known methods or conditions, but the pH is preferably 0.0 to 2.0, and the oxidation-reduction potential (ORP value, silver / silver chloride electrode reference) may be 0 mV or less.

[0031] The leaching residue remaining undissolved by leaching with an acid can be separated from the metal-containing solution by solid-liquid separation such as filtration by known devices and methods such as a filter press or a thickener. Much of the copper in the battery powder may be included in the leaching residue. This solid-liquid separation can be omitted, and a metal separation step such as neutralization may be performed without solid-liquid separation after leaching.

[0032] In the acid leaching process, a metal-containing solution containing lithium ions and other metal ions is obtained. The other metal ions may be at least one selected from the group consisting of cobalt ions, nickel ions, manganese ions, aluminum ions, iron ions, and copper ions, and typically, cobalt ions and / or nickel ions are included. The metal-containing solution may further contain fluoride ions.

[0033] The metal-containing solution obtained in the acid leaching process may have a cobalt ion concentration of 10 g / L to 50 g / L, a nickel ion concentration of 10 g / L to 50 g / L, a manganese ion concentration of 0 g / L to 50 g / L, an aluminum ion concentration of 1.0 g / L to 20 g / L, an iron ion concentration of 0.1 g / L to 5.0 g / L, a copper ion concentration of 0.005 g / L to 0.2 g / L, and a fluoride ion concentration of 0.01 g / L to 20 g / L. This metal-containing solution is subjected to the metal separation process described below.

[0034] (Neutralization) When the metal-containing solution obtained in the acid leaching process contains aluminum ions and / or iron ions, in the metal separation process, first, neutralization can be carried out to raise the pH of the metal-containing solution and separate the neutralization residue to obtain a post-neutralization solution. The neutralization may include an aluminum removal stage and an iron removal stage. However, in cases where the metal-containing solution does not contain aluminum ions and / or iron ions, the aluminum removal stage and / or the iron removal stage may be omitted.

[0035] In the aluminum removal stage, by raising the pH of the metal-containing solution, at least a part of the aluminum ions is precipitated and removed by solid-liquid separation. At this time, for example, when the liquid temperature is 50°C to 90°C and the pH is raised to the range of 2.5 to 5.0, particularly 3.0 to 4.5, with a pH adjuster, aluminum ions can be effectively separated while suppressing the precipitation of nickel ions and / or cobalt ions.

[0036] Until the aluminum removal step is completed, it is preferable to add a phosphate ion source. Thereby, in the aluminum removal step, aluminum ions in the metal-containing solution react with phosphate ions, and the aluminum ions precipitate as aluminum phosphate or the like, and this can be removed by solid-liquid separation. The timing of adding the phosphate ion source is not particularly limited. If phosphate ions are present in the metal-containing solution in the aluminum removal step, the above reaction occurs in the aluminum removal step. Examples of the phosphate ion source include phosphoric acid (H3PO4) and the like.

[0037] In the iron removal step, an oxidizing agent is added, and a pH adjuster is further added to raise the pH. Thereby, iron ions are oxidized from divalent to trivalent and precipitate as a solid such as an oxide or iron hydroxide (Fe(OH)3), and this can be removed by solid-liquid separation. The oxidation-reduction potential (ORP value, silver / silver chloride electrode reference) during oxidation is preferably 300 mV to 900 mV. The oxidizing agent is not particularly limited as long as it can oxidize iron, but it is preferably manganese dioxide, a positive electrode active material, and / or a manganese-containing leaching residue obtained by leaching the positive electrode active material. The manganese-containing leaching residue obtained by leaching the positive electrode active material with an acid may contain manganese dioxide. When the above positive electrode active material or the like is used as the oxidizing agent, a precipitation reaction occurs in which manganese dissolved in the liquid becomes manganese dioxide, so that the precipitated manganese can be removed together with iron.

[0038] Examples of the pH adjuster used in neutralization such as the above-mentioned aluminum removal step and iron removal step include lithium hydroxide, sodium hydroxide, sodium carbonate, ammonia, etc., but it is preferable to use a lithium hydroxide solution obtained in the electrodialysis step described later. In this case, lithium ions circulate within the wet treatment.

[0039] (Manganese and other extraction step) The metal-containing solution can extract and remove manganese ions by solvent extraction after the above-mentioned neutralization if necessary. Here, when the metal-containing solution contains aluminum ions, not only manganese ions but also aluminum ions are extracted and removed.

[0040] For the extraction of manganese ions, it is preferable to use an extractant containing a phosphoric acid-based extractant, more specifically a phosphoric acid ester-based extractant. Specific examples of the phosphoric acid ester-based extractant include di-2-ethylhexyl phosphoric acid (abbreviation: D2EHPA or trade name: DP8R). When a phosphoric acid-based extractant is used, phosphorus is likely to be contained as an impurity in the metal-containing solution as the post-extraction solution obtained after manganese extraction, and further in the metal-containing solution in the subsequent electrodialysis process.

[0041] In addition, the extractant may be a mixture of an oxime-based extractant in addition to the phosphoric acid ester-based extractant. In this case, the oxime-based extractant is preferably an aldoxime or one mainly composed of aldoxime. Specifically, for example, 2-hydroxy-5-nonylacetophenone oxime (trade name: LIX84), 5-dodecylsalicylaldoxime (trade name: LIX860), a mixture of LIX84 and LIX860 (trade name: LIX984), 5-nonylsalicylaldoxime (trade name: ACORGAM5640), etc.

[0042] The extractant may be diluted to a concentration of 10% to 30% by volume using a hydrocarbon-based organic solvent such as an aromatic-based, paraffin-based, or naphthene-based solvent, and used as the solvent.

[0043] During extraction, the equilibrium pH is preferably set to 2.3 to 3.5, more preferably 2.5 to 3.0. It is preferable to use the lithium hydroxide aqueous solution obtained in the electrodialysis process described later as the pH adjuster used at this time.

[0044] Upon extraction, it is desirable to perform extraction by countercurrent multi-stage extraction in which the flow directions of the aqueous phase and the solvent used for each extraction are opposite. By doing so, the extraction of cobalt ions, nickel ions, and lithium ions can be suppressed, and the extraction rate of manganese ions can be increased. In the case of countercurrent multi-stage extraction, for example, it is effective to set the equilibrium pH during the first-stage extraction to a value within the above range and lower the equilibrium pH during extraction with each successive stage. However, if extraction is performed in multiple stages, since the number of contacts between the extractant and the metal-containing solution increases, the amount of phosphorus derived from the phosphoric acid-based extractant mixed into the metal-containing solution may increase.

[0045] Since the solvent extracted with manganese ions may contain cobalt ions, nickel ions, and lithium ions, these ions that may be contained in the solvent are extracted into the aqueous phase by scrubbing, back-extraction, and scavenging. The scrubbing solution can be, for example, a sulfuric acid solution, and the pH can be set to 2.0 to 3.0. The back-extraction solution can be, for example, a sulfuric acid solution, and the pH can be set to 0.0 to 1.0. The solution after scrubbing, the solution after back-extraction, and the solution after scavenging are desirably used in the manganese extraction process (for example, the solution after scrubbing is mixed with the metal-containing solution and used as the pre-extraction solution for solvent extraction in the manganese extraction process, the solution after back-extraction is used for scrubbing in the manganese extraction process, or the solution after scavenging is used as the back-extraction solution in the manganese extraction process). Thereby, cobalt ions, nickel ions, and lithium ions can be circulated or retained in the process without loss. However, in particular, the solution after scrubbing may contain a large amount of fluoride ions and phosphorus. If such a solution after scrubbing is mixed with the pre-extraction solution and circulated, the fluoride ions and phosphorus removed from the solvent by scrubbing will return to the metal-containing solution, so fluoride ions and phosphorus may easily remain until the electrodialysis process. Note that if the solvent extracted with manganese ions does not contain cobalt ions, nickel ions, and lithium ions, scrubbing, back-extraction, and scavenging may not be performed.

[0046] (Cobalt Extraction and Crystallization) For example, after extracting manganese ions, cobalt ions can be extracted and separated from the manganese-extracted solution (metal-containing solution) by solvent extraction.

[0047] For the extraction of cobalt ions, it is preferable to use a solvent containing a phosphoric acid-based extractant, especially a phosphonate ester-based extractant. In particular, 2-ethylhexyl 2-ethylhexylphosphonate (trade name: PC-88A, Ionquest 801) is suitable from the viewpoints of separation efficiency between nickel and cobalt, etc. The extractant can be diluted with a hydrocarbon-based organic solvent so that the concentration is 10% to 30% by volume and used as a solvent. Here, when using a phosphoric acid-based extractant, phosphorus is likely to be contained as an impurity in the metal-containing solution as the cobalt-extracted solution and the metal-containing solution in which the subsequent electrodialysis process is performed.

[0048] When extracting cobalt ions, the equilibrium pH during extraction is preferably 5.0 to 6.0, more preferably 5.0 to 5.5. When the pH is less than 5.0, there is a possibility that cobalt ions cannot be sufficiently extracted into the solvent. As the pH adjuster at this time, it is preferable to use an aqueous lithium hydroxide solution obtained in the electrodialysis process described later.

[0049] Also when extracting cobalt ions, it is desirable to perform extraction by countercurrent multi-stage extraction in which the flow directions of the aqueous phase and the solvent used for each extraction are opposite. By doing so, the extraction rate of cobalt ions can be increased while suppressing the extraction of nickel ions and lithium ions. However, if there are multiple stages of extraction, the number of contacts between the extractant and the metal-containing solution increases, so the amount of phosphorus mixed into the metal-containing solution from the phosphoric acid-based extractant may increase.

[0050] During the above extraction, not only cobalt ions but also some nickel ions and lithium ions may be extracted into the solvent. In this case, if necessary, the solvent from which cobalt ions have been extracted may be scrubbed one or more times using a scrubbing solution to remove nickel ions and lithium ions that may be contained in the solvent. The scrubbing solution can be, for example, a sulfuric acid solution, and the pH can be set to 3.5 to 5.5. The scrubbed solution may contain nickel ions and lithium ions. Therefore, it is desirable to mix a part or all of the scrubbed solution with the solution after manganese extraction and use it as the solution before extraction to extract cobalt ions. This enables the recycling or retention of nickel ions and lithium ions within the wet treatment process without loss. However, in particular, the scrubbed solution may contain a large amount of fluoride ions and phosphorus. If such a scrubbed solution is mixed with the solution before extraction and recycled, the fluoride ions and phosphorus removed from the solvent by scrubbing will return to the metal-containing solution, and thus fluoride ions and phosphorus may tend to remain until the electrodialysis step. If the solvent from which cobalt ions have been extracted does not contain nickel ions and lithium ions, the scrubbing step may not be necessary.

[0051] Thereafter, back-extraction is performed on the solvent from which cobalt ions have been extracted. The back-extraction solution used for back-extraction may be any of inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid, but sulfuric acid is desirable when obtaining sulfate by crystallization in the next step. Here, the back-extraction is carried out under pH conditions such that as much cobalt ion as possible migrates from the solvent to the back-extraction 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.

[0052] The reverse extraction solution can be crystallized. Here, the reverse extraction solution is heated to, for example, 40°C to 120°C and concentrated. As a result, cobalt ions crystallize, and cobalt salts such as cobalt sulfate are obtained. The cobalt salt thus obtained has a nickel content of preferably 5 mass ppm or less, and since nickel has been sufficiently removed, it can be effectively used as a raw material for the manufacture of lithium-ion secondary batteries and other batteries. Here, the crystallized solution may contain cobalt ions and lithium ions that did not crystallize. Therefore, the crystallized solution can be mixed with the reverse extraction solution before crystallization and subjected to crystallization again, used to adjust the cobalt ion concentration of the scrubbing solution used in the solvent for extracting cobalt ions, or mixed with the solution after manganese extraction and subjected to cobalt ion extraction. In this way, cobalt ions and lithium ions can be circulated or retained within the wet treatment without loss and concentrated.

[0053] (Nickel extraction and crystallization) Solvent extraction can be performed on the cobalt extraction solution (metal-containing solution) after cobalt ions have been extracted to extract nickel ions.

[0054] In the extraction of nickel ions, a carboxylic acid-based extractant is preferably used to separate nickel ions from the cobalt extraction solution. Examples of carboxylic acid-based extractants include neodecanoic acid and naphthenic acid, among which neodecanoic acid is preferred due to its ability to extract nickel ions. The extractant may be diluted to a concentration of 10% to 30% by volume using a hydrocarbon-based organic solvent such as an aromatic, paraffinic, or naphthenic solvent, and used as the solvent.

[0055] The equilibrium pH during extraction is preferably 6.0 to 8.0, more preferably 6.8 to 7.2. As the pH adjuster used for adjusting the pH at this time, it is preferable to use an aqueous lithium hydroxide solution obtained in the electrodialysis step described later. When extracting nickel ions, it is desirable to perform countercurrent multi-stage extraction. By doing so, the extraction of lithium ions is suppressed, and the extraction rate of nickel ions can be increased.

[0056] For the solvent from which nickel ions have been extracted, if necessary, one or more scrubbings may be performed to remove lithium ions that may be contained in the solvent using a scrubbing solution. The scrubbing solution can be, for example, a sulfuric acid solution, and the pH can be 5.0 to 6.0. Here, the scrubbed solution may contain lithium ions. Therefore, it is desirable to mix part or all of the scrubbed solution with the solution after cobalt extraction and use it as the pre-extraction solution to extract nickel ions. Thereby, it is possible to circulate or retain and concentrate within the wet treatment without losing lithium ions. However, if the solvent from which nickel ions have been extracted does not contain lithium ions, scrubbing may not be necessary.

[0057] Thereafter, back-extraction is performed on the solvent using a back-extraction solution such as sulfuric acid, hydrochloric acid, or nitric acid. When crystallization is performed thereafter, sulfuric acid is particularly desirable. The pH is preferably in the range of 1.0 to 3.0, more preferably 1.5 to 2.5. Regarding the O / A ratio and the number of times, they can be determined appropriately, but the O / A ratio is 5 to 1, more preferably 4 to 2.

[0058] When a stripping post-liquid such as a nickel sulfate solution is obtained by reverse extraction, after electrolysis and dissolution are carried out as necessary, it is heated to 40°C to 120°C for crystallization, and nickel ions can be crystallized as nickel salts such as nickel sulfate. Thereby, a nickel salt can be obtained. Here, the post-crystallization liquid may contain nickel ions and lithium ions that did not crystallize. Therefore, the post-crystallization liquid is preferably mixed with the post-reverse extraction liquid before crystallization and subjected to re-crystallization, used to adjust the nickel ion concentration of the scrubbing liquid for the solvent from which nickel ions have been extracted, or mixed with the post-cobalt extraction liquid and used for nickel ion extraction. By repeatedly using it within the process in this way, nickel ions and lithium ions can be circulated or retained and concentrated within the wet treatment without loss.

[0059] The post-nickel extraction liquid after nickel ions are extracted mainly contains lithium ions and may be added to the acidic leaching liquid in the acid leaching step. Thereby, the lithium ions contained in the post-nickel extraction liquid can be circulated within a series of steps from acid leaching to nickel extraction. Preferably, after the lithium ions are circulated in this way and the lithium ion concentration of the post-nickel extraction liquid becomes somewhat high, the electrodialysis step described below can be performed.

[0060] (Electrodialysis step) The metal-containing solution such as the post-nickel extraction liquid obtained in the above-described metal separation step has had metals other than lithium ions and impurities sufficiently separated and mainly contains lithium ions.

[0061] The metal-containing solution contains, as impurities, for example, fluoride ions (F -) is included. The impurities may also include phosphorus (P). Phosphorus tends to be included particularly when multiple solvent extractions such as manganese extraction and cobalt extraction are performed as described above, due to the inclusion of the phosphoric acid-based extractant used in the extraction in the liquid. Also, as described above, when a phosphate ion source is added in order to sufficiently separate aluminum ions at the dealumination stage of the neutralization process, the metal-containing solution may contain a certain amount of phosphorus as an impurity. Other impurities may include silicon derived from glass fibers in lithium-ion battery waste, for example.

[0062] The metal-containing solution may contain a small amount of cations such as nickel ions and magnesium ions that could not be completely separated in the metal separation process. Nickel ions and magnesium ions are cations like lithium ions, and behave similarly to lithium ions during electrodialysis, making it difficult to separate them from lithium ions. In addition, when electrodialysis is performed on a metal-containing solution containing nickel ions and magnesium ions, nickel and magnesium hydroxides may be generated in the lithium hydroxide solution obtained, and there is a concern that electrodialysis may not be able to be continued due to process troubles. For this reason, in such a case, it is desirable to perform washing to remove cations such as nickel ions and magnesium ions from the metal-containing solution prior to the electrodialysis described below. For example, an ion exchange resin or a chelating resin can be used for this washing.

[0063] The metal-containing solution before the electrodialysis step may have, for example, a lithium ion concentration of 1.0 g / L to 30.0 g / L, a fluoride ion concentration of 0.01 g / L to 5.0 g / L, a phosphorus concentration of 0.001 g / L to 1.0 g / L, and a silicon concentration of 0.001 g / L to 1.0 g / L.

[0064] When obtaining a lithium hydroxide solution from the above metal-containing solution, if carbonation and chemical conversion methods are applied, impurities may remain in the lithium hydroxide solution without being removed. Using a lithium hydroxide solution containing a large amount of impurities in the metal separation step as a pH adjuster is not desirable because not only lithium ions but also impurities will circulate or accumulate in the wet process.

[0065] Therefore, in this embodiment, an electrodialysis step is performed on the metal-containing solution to obtain a lithium hydroxide solution and an acidic solution from the metal-containing solution. As a result, since most of the impurities are contained in the acidic solution, a lithium hydroxide solution with sufficient impurity removal can be obtained.

[0066] The electrodialysis step can be performed, for example, using a commercially available bipolar membrane electrodialysis device. As an example, the bipolar membrane electrodialysis device 1 shown in FIG. 3 (hereinafter, also simply referred to as "electrodialysis device 1") has an anode 2 and a cathode 3 in the cell, and between these anodes 2 and 3, a bipolar membrane 4, an anion exchange membrane 5, a cation exchange membrane 6, and a bipolar membrane 7 are sequentially arranged from the anode 2 side to the cathode 3 side. Thereby, the inside of the cell is partitioned into a desalting chamber R1 between the anion exchange membrane 5 and the cation exchange membrane 6, an acid chamber R2 between the bipolar membrane 4 and the anion exchange membrane 5, and an alkali chamber 3a between the cation exchange membrane 6 and the bipolar membrane 7. The bipolar membranes 4 and 7 are each composed of a stacked cation exchange layer and anion exchange layer.

[0067] To perform electrodialysis with the illustrated electrodialysis device 1, a metal-containing solution is placed in the desalting chamber R1, pure water is placed in each of the acid chamber R2 and the alkali chamber R3, and a predetermined voltage is applied between the anode 2 and the cathode 3. Then, lithium ions (Li + ) in the metal-containing solution in the desalting chamber R1 pass through the cation exchange membrane 6 and move to the alkali chamber R3. In the alkali chamber R3, water (H2O) is decomposed by the bipolar membrane 7, and since hydroxide ions (OH - ) exist, a lithium hydroxide solution can be obtained.

[0068] On one hand, the anions of the inorganic acid in the metal-containing solution in the desalting chamber R1 pass through the anion exchange membrane 5 and move to the acid chamber R2. In the acid chamber R2, the anions react with hydrogen ions (H + ) generated from water (H2O) by the bipolar membrane 4 to form an acidic solution such as a sulfuric acid solution. As a result, the lithium hydroxide solution obtained in the alkali chamber R3 contains almost no anions of the inorganic acid. In the example shown in the figure, the anions of the inorganic acid are sulfate ions (SO4 2- ), but depending on the type of acid used in the acid leaching process, etc., they may be nitrate ions (NO3 - ) or chloride ions (Cl - ).

[0069] In the desalting chamber R1, as described above, the lithium salt is separated from the metal-containing solution, and a post-desalting solution remains. The concentration of the anions of the inorganic acid tends to be higher in the acidic solution than in the lithium hydroxide solution, and also higher in the post-desalting solution than in the lithium hydroxide solution.

[0070] In this electrodialysis, most of the fluoride ions of the impurities in the metal-containing solution pass through the anion exchange membrane 5 from the desalting chamber R1 to the acid chamber R2 and are contained in the acidic solution. Also, the impurity silicon can migrate to the acidic solution. As a result, in the alkali chamber R3, a lithium hydroxide solution containing almost no fluoride ions and silicon is obtained. Therefore, the fluoride ion concentration of the lithium hydroxide solution is lower than that of the acidic solution.

[0071] Regarding phosphorus, which is an impurity in the metal-containing solution, it has been found that most of it does not pass through either the cation exchange membrane 6 or the anion exchange membrane 5 and remains in the desalting chamber R1. Therefore, the lithium hydroxide solution obtained by electrodialysis contains almost no phosphorus. Therefore, the phosphorus concentration of the post-desalting solution remaining in the desalting chamber R1 after the lithium salt is separated from the metal-containing solution is higher than that of the lithium hydroxide solution.

[0072] The lithium hydroxide solution from which impurities have been removed by electrodialysis as described above can be effectively used as a pH adjuster in the metal separation step. After electrodialysis, if necessary, the lithium ion concentration of the lithium hydroxide solution can be increased by heating and concentration or the like, and then this can be used as a pH adjuster.

[0073] (Crystallization step) A part of the lithium hydroxide solution obtained in the electrodialysis step can be subjected to the crystallization step. For example, when the lithium hydroxide solution is returned to the wet treatment as a pH adjuster as described above, the lithium ion concentration in the solution may gradually increase due to the lithium in the battery powder newly introduced into the wet treatment. Depending on the lithium ion concentration, a crystallization step may be performed to recover lithium hydroxide.

[0074] In the crystallization step, in order to precipitate lithium hydroxide, crystallization operations such as heating and concentration or vacuum distillation can be performed. In the case of heating and concentration, the higher the temperature during crystallization, the faster the treatment progresses, which is preferable. However, after crystallization, the temperature during drying of the crystallized product is preferably less than 60°C at which crystal water does not desorb. This is because anhydrous lithium hydroxide from which crystal water has desorbed has deliquescence and is difficult to handle.

[0075] As described above, the lithium hydroxide solution obtained in the electrodialysis step substantially does not contain anions of inorganic acids such as sulfate ions. Therefore, the lithium hydroxide produced in the crystallization step has high purity and excellent quality.

[0076] Thereafter, the above lithium hydroxide can be subjected to a grinding treatment or the like in order to adjust it to required physical properties.

Example

[0077] Next, the above-described impurity removal method was experimentally implemented to confirm its effect, and the results will be described below. However, this description is for illustrative purposes only and is not intended to be limiting.

[0078] Neutralization, manganese extraction, cobalt extraction, and nickel extraction were performed on the metal-containing solution obtained by leaching battery powder with sulfuric acid to separate each metal.

[0079] Next, electrodialysis was performed on the separated metal-containing solution using a bipolar membrane electrodialysis device (manufactured by Asahi Kasei Corporation) having a structure as shown in Fig. 3. Here, a metal-containing solution, pure water, and an electrode solution having the compositions shown in Fig. 4 were placed in the desalting chamber, alkali chamber, acid chamber, and electrode chamber, respectively. The condition of electrodialysis was a constant voltage of 32V.

[0080] The results are also shown in Fig. 4. In Fig. 4, the reason why the sum of the distribution ratios of each ion in the desalted solution, lithium hydroxide solution, acidic solution, and electrode solution after electrodialysis does not reach 100% is considered to be due to variations in the analytical values (including the part that could not be quantified due to the lower limit of quantification of the analysis, etc.).

[0081] From Fig. 4, it can be seen that the fluoride ion concentration, phosphorus concentration, and silicon concentration in the lithium hydroxide solution obtained after electrodialysis are all sufficiently low. From this, it can be seen that an almost impurity-free lithium hydroxide solution can be obtained by electrodialysis.

[0082] From the above, it was found that according to the impurity removal method described above, impurities such as fluoride ions can be effectively removed.

Explanation of symbols

[0083] 1 Bipolar membrane electrodialysis device 2 Anode 3 Cathode 4, 7 Bipolar membranes 5 Anion exchange membrane 6 Cation exchange membrane R1 Desalting chamber R2 Acid chamber R3 Alkali chamber

Claims

1. A method for removing impurities from a metal-containing solution obtained by leaching battery powder of lithium-ion battery waste with an acid, comprising: a metal separation step of separating other metal ions from the metal-containing solution containing lithium ions and other metal ions; after the metal separation step, an electrodialysis step of performing electrodialysis using a bipolar membrane on the metal-containing solution containing lithium ions and fluoride ions of impurities to obtain a lithium hydroxide solution and an acidic solution; and using the lithium hydroxide solution as a pH adjuster in the metal separation step, the impurity removal method.

2. The impurity removal method according to claim 1, wherein the fluoride ion concentration of the lithium hydroxide solution is lower than the fluoride ion concentration of the acidic solution.

3. The metal separation step includes separating the other metal ions from the metal-containing solution by solvent extraction, and using the lithium hydroxide solution as a pH adjuster in the solvent extraction, the impurity removal method according to claim 1.

4. The metal-containing solution contains a plurality of types of the other metal ions, and in the metal separation step, a plurality of solvent extractions are performed according to the types of the other metal ions, the impurity removal method according to claim 3.

5. The other metal ions include cobalt ions and / or nickel ions, and in the metal separation step, cobalt ions and / or nickel ions are separated from the metal-containing solution by solvent extraction, the impurity removal method according to claim 3.

6. The other metal ions include manganese ions and / or aluminum ions, and in the metal separation step, manganese ions and / or aluminum ions are separated from the metal-containing solution by solvent extraction, the impurity removal method according to claim 3.

7. In the metal separation step, a phosphoric acid-based extractant is used in the solvent extraction, and the impurities contained in the metal-containing solution further contain phosphorus, the impurity removal method according to claim 3.

8. The impurity removal method according to claim 7, wherein the phosphorus concentration of the desalted solution obtained by separating the lithium salt from the metal-containing solution in the electrodialysis step is higher than the phosphorus concentration of the lithium hydroxide solution.

9. The other metal ions include aluminum ions and / or iron ions, The impurity removal method according to claim 1, wherein in the metal separation step, aluminum ions and / or iron ions are separated from the metal-containing solution by neutralization, and the lithium hydroxide solution is used as a pH adjuster for the neutralization.

10. The other metal ions include aluminum ions, and the neutralization step includes an aluminum removal stage. A phosphate ion source is added until the aluminum removal stage ends, and phosphate ions are present in the metal-containing solution. The impurity removal method according to claim 1, wherein in the aluminum removal stage, aluminum ions in the metal-containing solution are reacted with phosphate ions to separate aluminum ions from the metal-containing solution.

11. A method for recovering metals from battery powder of lithium-ion battery waste, which uses the impurity removal method according to any one of claims 1 to 9.

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