WO2024014540A1

WO2024014540A1 - Method for removing impurities, and method for recovering metals

Info

Publication number: WO2024014540A1
Application number: PCT/JP2023/026110
Authority: WO
Inventors: Junichi ARAKAWA; Hiromichi KASHIMURA; Eriko KAMIYAMA
Original assignee: JX Metals Corp
Current assignee: JX Advanced Metals Corp
Priority date: 2022-07-14
Filing date: 2023-07-14
Publication date: 2024-01-18
Anticipated expiration: 2025-01-14
Also published as: JP2025521410A

Abstract

Provided are a method for removing impurities that can effectively remove impurities such as fluoride ions, and a method for recovering metals. The method for removing impurities from a metal-containing solution obtained by leaching battery powder of lithium ion battery waste with an acid, the method including: a metal separation step of separating other metal ions from the metal-containing solution containing lithium ions and the other metal ions; and, after the metal separation step, an electrodialysis step of subjecting the metal-containing solution containing lithium ions, and fluoride ions as impurities, to electrodialysis using a bipolar membrane to obtain a lithium hydroxide solution and an acidic solution, wherein the lithium hydroxide solution is used as a pH adjusting agent in the metal separation step.

Description

METHOD FOR REMOVING IMPURITIES, AND METHOD FOR RECOVERING METALS

This specification discloses a method for removing impurities, and a method for recovering metals.

In recent years, it has been widely studied for recovery of valuable metals such as cobalt and nickel contained in lithium ion battery waste discarded for expired product life, manufacturing defects or other reasons, in terms of effective utilization of resources.

The process of recovering valuable metals from lithium ion battery waste can include, for example, roasting or other predetermined dry processes of lithium ion battery waste, and wet processes of the battery powder obtained after the dry processes.

Specifically, in the wet processes, 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 containing the metals dissolved. Aluminum ions, iron ions, manganese ions, and the like are then sequentially or simultaneously removed from the metal-containing solution by neutralization or solvent extraction, as described, for example, in Patent Literature 1. Cobalt ions and nickel ions in the metal-containing solution are then separated by solvent extraction. After separating the nickel ions by extraction, a metal-containing solution is obtained in which lithium ions remain.

WO 2018/181816 A1

By the way, the neutralization and solvent extraction as described above employ a pH adjusting agent for adjusting a pH by increasing it. Although the pH adjusting agent can be used by separately preparing sodium hydroxide or the like, it is desirable to use a lithium hydroxide solution prepared from the metal-containing solution obtained after solvent extraction of cobalt ions and/or nickel ions or other metals. This can prevent contamination of sodium or the like derived from the separately prepared pH adjusting agent, and also the cost of the pH adjusting agent to be reduced.

However, the metal-containing solution contains impurities such as fluoride ions. If such a metal-containing solution is used as a lithium hydroxide solution and circulated in a metal recovery process using it as a pH adjusting agent, there is a risk that the impurities as described above are accumulated and concentrated, affecting the process.

This specification provides a method for removing impurities that can effectively remove impurities such as fluoride ions, and a method for recovering metals.

A method for removing impurities disclosed herein is a method for removing impurities from a metal-containing solution obtained by leaching battery powder of 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 the other metal ions; and, after the metal separation step, an electrodialysis step of subjecting the metal-containing solution containing lithium ions and fluoride ions as impurities, to electrodialysis using a bipolar membrane to obtain a lithium hydroxide solution and an acidic solution, wherein the lithium hydroxide solution is used as a pH adjusting agent in the metal separation step.

Also, the method for recovering metals disclosed herein is a method for recovering metals from battery powder of lithium ion battery waste, the method comprising using the method for removing impurities as described above.

According to the method for removing impurities as described above, it is possible to effectively remove impurities such as fluoride ions.

Fig. 1 is a flow chart showing an example of a method for recovering metals including an impurity removal method according to an embodiment. Fig. 2 is a flow chart showing an example of a preprocessing step for obtaining battery powder from lithium ion battery waste. Fig. 3 is a cross-sectional view schematically showing an example of a bipolar membrane electrodialysis device that can be used in an electrodialysis step included in an impurity removal method according to an embodiment. Fig. 4 is a view showing components of each solution before and after electrodialysis in Example.

Embodiments of the method for removing impurities and the method for recovering metals described above will be described below in detail.
An embodiment of the method for removing impurities is a method for removing impurities from a metal-containing solution obtained by leaching battery powder of lithium ion battery waste with an acid. The method includes: a metal separation step of separating other metal ions from the metal-containing solution containing lithium ions and the other metal ions; and, after the metal separation step, an electrodialysis step of subjecting the metal-containing solution containing lithium ions and fluoride ions as impurities to electrodialysis using a bipolar membrane to obtain a lithium hydroxide solution and an acidic solution. The lithium hydroxide solution is used as a pH adjusting agent in the metal separation step.

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 substantially absent from the lithium hydroxide solution and effectively removed. As a result, accumulation and concentration of fluoride ions can be suppressed when the lithium hydroxide solution is used as a pH adjusting agent in the metal separation step and circulated in the wet processes of the method for recovering metals. Further, anions of inorganic acids such as sulfate ions, nitrate ions, and chloride ions also migrate to the acidic solution and are substantially absent from the lithium hydroxide solution, so that a lithium hydroxide solution having high purity can be obtained. This significantly contributes to improvement of the quality of lithium hydroxide.

The method for recovering metals according to the embodiment as described herein, as illustrated in Fig. 1, carries out, as a wet process, the 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 metal separation step and the electrodialysis step as described above. The lithium hydroxide solution obtained in the electrodialysis step is optionally concentrated and then used as a pH adjusting agent in the metal separation step. In Fig. 1, the metal separation step includes neutralization, solvent extraction of manganese and/or aluminum ions (Mn etc. Extraction), solvent extraction of cobalt ions, and solvent extraction of nickel ions. However, depending on the type of metal ions other than lithium ions contained in the metal-containing solution, at least one of the neutralization and multiple solvent extraction processes may be omitted.

(Lithium Ion Battery Waste)
The lithium ion battery waste of interest is lithium ion secondary batteries which can be used in various electronic devices such as mobile phones and which have been discarded due to the expired life of the product, manufacturing defects or other reasons. The recovery of valuable metals from such lithium ion battery waste is preferred in terms of effective utilization of resources.

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

The lithium ion battery waste may also contain, in the above housing, cathode active materials composed of one single metal oxide containing lithium and one selected from the group consisting of nickel, cobalt and manganese, or a composite metal oxides containing lithium and two or more of those, or the like, and aluminum foils (cathode substrates) to which the cathode active materials are applied and fixed by, for example, polyvinylidene fluoride (PVDF) or other organic binders. In addition, the lithium ion battery waste may contain copper, iron, or the like.

Further, the housing of the lithium ion battery waste generally contains an electrolytic solution having an electrolyte such as lithium hexafluorophosphate dissolved in an organic solvent. For example, ethylene carbonate, diethyl carbonate or the like may be used as the organic solvent.

(Preprocessing)
In many cases, the lithium ion battery waste is subjected to preprocessing as a dry process. The preprocessing may include at least one of roasting, crushing and sieving. The lithium ion battery waste becomes battery powder through the preprocessing. The roasting, crushing, and sieving in the preprocessing step may optionally be performed, respectively, or they may be performed in any order. In the example shown in Fig. 2, the roasting, crushing and sieving are performed in this order.

It should be noted that the battery powder means a powder obtained by subjecting the lithium ion battery waste to any process to concentrate cathode material components. The battery powder may be obtained as a powder by crushing and sieving the lithium ion battery waste with or without a heat treatment to concentrate the cathode material components.

In the roasting, the above lithium ion battery waste is heated. When the roasting is carried out, metals such as lithium and cobalt contained in the lithium ion battery waste is changed to an easily dissolvable form. During the roasting, the lithium ion battery waste is preferably heated by maintaining it in a temperature range of, for example, from 450°C to 1000°C, further in a temperature range of from 600°C to 800°C, for 0.5 to 4 hours. The roasting can be carried out in either an air atmosphere or an inert atmosphere such as nitrogen, and in the air atmosphere and the inert atmospheres in this order or vice versa. The roasting can be of batch type or continuous type. For example, the batch type includes a stationary furnace, the continuous type includes a rotary kiln furnace, and other various types of furnaces can also be used.

During the roasting, at least a part of the electrolytic solution is removed from the lithium ion battery waste because the electrolytic solution is evaporated, or the like. In many cases, when the lithium ion battery waste is heated during the roasting, the components of the internal electrolyte are sequentially evaporated, starting with the component having a lower boiling point. Also, when the temperature of the lithium ion battery waste reaches a higher temperature, the resin such as the organic binder is decomposed or vaporized. Even if a part of the electrolyte and the organic binder is thus removed, a certain component such as fluorine contained in the electrolyte and the organic binder remains and may be contained in the battery powder obtained after the preprocessing step. When the roasting is carried out, the electrolytic solution is removed and rendered harmless, and the organic binder is decomposed to promote separation between the aluminum foil and the cathode active material during crushing and sieving, which will be described below. Although the roasting changes the composition of the cathode active material, the roasted material is also referred to as the cathode active material.

After the roasting, the crushing can be carried out to remove cathode materials and the like from the housing of the lithium ion battery waste. The crushing selectively separates the cathode active materials from the aluminum foils to which the cathode active materials are applied, while destroying the housing of the lithium ion battery waste.

Various known apparatuses or devices can be used in the crushing. In particular, it is preferable to use an impact-type crusher that can crush lithium ion battery waste by applying an impact while cutting it. Examples of the impact-type crusher include a sample mill, a hammer mill, a pin mill, a wing mill, a tornado mill, and a hammer crusher. It should be noted that a screen can be installed at an outlet of the crusher, whereby the lithium ion battery waste is discharged from the crusher through the screen when crushed to a size that can pass through the screen.

After crushing the lithium ion battery waste, the sieving is performed by sieving it using a sieve having an appropriate opening. Thus, aluminum or copper remains on the sieve, and battery powder from which Al or Cu has been removed to some extent can be obtained under the sieve.

The battery powder obtained in the preprocessing step contains lithium, and in addition to lithium, at least one other metal selected from the group consisting of cobalt, nickel, manganese, aluminum, iron and copper. 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. The battery powder may also contain 0.1% by mass to 10% by mass of fluorine.

The battery powder can be brought into contact with water prior to an acid leaching step as described below, in order to extract substantially only lithium from the battery powder. Lithium in the battery powder is thus leached into the water. In this case, the battery powder as the water leached residue is subjected to the acid leaching step. However, when the water leaching is carried out, the equipment is required, and the processing time increases by performing both the water leaching and the acid leaching in the acid leaching step, as well as it may be necessary to manage the roasting conditions for effectively leaching lithium with water. Further, even with such management, the leaching rate of lithium with water may not be significantly increased. Therefore, the battery powder obtained as described above may be subjected to acid leaching in the acid leaching step without the water leaching. When the water leaching is not carried out, the lithium ion concentration in the liquid can be easily maintained at a higher level in wet processes after the acid leaching step.

(Acid Leaching Step)
In the acid leaching step, lithium and other metal contained in the lithium ion battery waste are leached with an acid by adding the above battery powder to an acidic leaching solution of sulfuric acid, nitric acid, hydrochloric acid or other inorganic acids.

The acid leaching step can be performed by a known method or conditions, but a pH is preferably 0.0 to 2.0, and an oxidation-reduction potential (ORP value, based on silver/silver chloride potential) may be 0 mV or less.

A leached residue that has remained after the acid leaching can be separated from the metal-containing solution by means of solid-liquid separation such as filtration using a known apparatus and method such as a filter press and a thickener. Most of the copper in the battery powder may be contained in the leached residue. The solid-liquid separation may be omitted, and the metal separation step such as neutralization may be performed after leaching without solid-liquid separation.

The acid leaching step provides the metal-containing solution containing lithium ions and other metal ions. 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, typically cobalt ions and/or nickel ions. The metal-containing solution may also contain fluoride ions.

The metal-containing solution obtained in the acid leaching step has 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. The metal-containing solution is subjected to the metal separation step described below.

(Neutralization)
When the metal-containing solution obtained in the acid leaching step contains aluminum ions and/or iron ions, first, the metal separation step carries out neutralization of increasing the pH of the metal-containing solution to separate a neutralized residue to obtain a neutralized solution. The neutralization may include an aluminum removal stage and an iron removal stage. However, if the metal-containing solution does not contain aluminum ions and/or iron ions, the aluminum removal step and/or iron removal step may be omitted.

In the aluminum removal step, the pH of the metal-containing solution is increased to precipitate at least a part of the aluminum ions and remove them by solid-liquid separation. At this time, for example, when the pH is increased in the range of 2.5 to 5.0, particularly 3.0 to 4.5 with a pH adjusting agent at a solution temperature of 50°C to 90°C, the aluminum ions can be effectively separated while suppressing precipitation of nickel ions and/or cobalt ions.

Preferably, a phosphate ion source is added during a period to the end of the aluminum removal step. As a result, in the aluminum removal step, aluminum ions and phosphate ions in the metal-containing solution react with each other to precipitate aluminum ions as aluminum phosphate or the like, which can be removed by solid-liquid separation. The timing of addition of the phosphate ion source is not particularly limited. If the phosphate ions are present in the metal-containing solution during the aluminum removal step, the above reaction will occur during the aluminum removal step. The phosphate ion sources include, for example, phosphoric acid (H₃PO₄).

In the iron removal step, an oxidizing agent is added and a pH adjusting agent is further added to increase the pH. As a result, the iron ions are oxidized from divalent to trivalent, and precipitated as a solid such as an oxide or iron hydroxide (Fe(OH)₃), which can be removed by solid-liquid separation. An 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 it may preferably be manganese dioxide, a cathode active material, and/or a manganese-containing leached residue obtained by leaching a cathode active material. The manganese-containing leached residue obtained by leaching the cathode active material with the acid may include manganese dioxide. When the cathode active material or the like is used as the oxidizing agent, it causes a precipitation reaction which converts manganese dissolved in the liquid to manganese dioxide, so that the precipitated manganese can be removed together with iron.

Examples of the pH adjusting agent used in neutralization in the above aluminum removal stage and iron removal step include lithium hydroxide, sodium hydroxide, sodium carbonate, and ammonia. A lithium hydroxide solution obtained in an electrodialysis step as described below is preferably used. In this case, lithium ions are circulated in the wet processes.

(Manganese etc. Extraction Step)
The metal-containing solution can be subjected to solvent extraction to extract and remove the manganese ions, through the above neutralization if necessary. Here, when the metal-containing solution contains aluminum ions, the manganese ions as well as the aluminum ions are extracted and removed.

In the extraction of the manganese ions, an extracting agent containing a phosphoric acid-based extracting agent, specifically a phosphate ester-based extracting agent, is preferably used. Here, specific examples of the phosphate ester-based extracting agent include di-2-ethylhexylphosphoric acid (abbreviated name: D2EHPA or trade name: DP8R). When the phosphoric acid-based extracting agent is used, phosphorus tends to be contained as an impurity in the metal-containing solution as the extracted solution obtained after the manganese extraction and further in the metal-containing solution to be subjected to the subsequent electrodialysis step.

Further, the extracting agent may be a mixture of the phosphate ester-based extracting agent and an oxime-based extracting agent. In this case, the oxime-based extracting agent is preferably aldoxime or based on aldoxime. Specific examples include 2-hydroxy-5-nonylacetophenone oxime (trade name: LIX84), 5-dodecyl salicylaldoxime (trade name: LIX860), a mixture of LIX84 and LIX860 (trade name: LIX984), 5-nonyl salicylaldoxime (trade name: ACORGAM5640) and the like.

The extracting agent may be diluted with an aromatic, paraffinic, naphthenic, or other hydrocarbon organic solvent to a concentration of 10% to 30% by volume and used as a solvent.

During extraction, an equilibrium pH is preferably 2.3 to 3.5, and more preferably 2.5 to 3.0. As the pH adjusting agent used at this time, it is preferable to use an aqueous lithium hydroxide solution obtained in an electrodialysis step as described below.

At the time of extraction, it is desirable to carry out extraction by countercurrent type multistage extraction in which directions of flow of the aqueous phase and the solvent used for each extraction are opposite to each other. 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 the countercurrent type multistage extraction, it is effective to set the equilibrium pH at the first stage of extraction to a value in the above range, and decrease the equilibrium pH at the time of extraction through successive stages. However, if the extraction is performed in multiple stages, the number of contacts of the extracting agent with the metal-containing solution increases, so that the amount of phosphorus derived from the phosphoric acid-based extracting agent mixed into the metal-containing solution may increase.

Since the solvent which has extracted the manganese ions may contain cobalt ions, nickel ions, and lithium ions, these ions that may be contained in the solvent are extracted into an aqueous phase by scrubbing, stripping, and scavenging. The scrubbing solution can be, for example, a sulfuric acid solution and can have a pH of 2.0 to 3.0. The stripping solution can be, for example, a sulfuric acid solution and can have a pH of 0.0 to 1.0. The scrubbed solution, the stripped solution, and the scavenged solution is preferably used in the manganese extraction step (for example, the scrubbed solution is mixed with the metal-containing solution and the mixture is used as a extracting solution to be subjected to the solvent extraction in the manganese extraction step, or the stripped solution is used for the scrubbing in the manganese extraction step, or the scavenged solution is used as the stripping solution in the manganese extraction step). As a result, the cobalt ions, nickel ions, and lithium ions can be circulated or retained in the steps without losing them. However, the scrubbed solution may contain large amounts of fluoride ions and phosphorus. When such a scrubbed solution is mixed with the extracting solution and circulated, the fluoride ions and phosphorus removed from the solvent by scrubbing are returned to the metal-containing solution, which tends to leave the fluoride ions and phosphorus until the electrodialysis step. If the solvent used to extract the manganese ions does not contain cobalt ions, nickel ions, or lithium ions, the scrubbing, stripping or scavenging may not be performed.

(Cobalt Extraction and Crystallization)
For example, after manganese ions are extracted, cobalt ions can be extracted and separated from a manganese extracted solution (metal-containing solution) by solvent extraction.

It is preferable to use a solvent containing a phosphoric acid-based extracting agent, especially a phosphonate ester-based extracting agent, for the extraction of the cobalt ions. Particularly, 2-ethylhexyl 2-ethylhexylphosphonate (trade name: PC-88A, Ionquest 801) is preferable from the viewpoint of separation efficiency between nickel and cobalt. The extracting agent may be diluted with a hydrocarbon-based organic solvent so as to have a concentration of 10% by volume to 30% by volume and used as a solvent. Here, when the phosphoric acid-based extracting agent is used, the metal-containing solution as the cobalt extracted solution and the metal-containing solution to be subjected to the subsequent electrodialysis step tend to contain phosphorus as an impurity.

When extracting the cobalt ions, the equilibrium pH during extraction is preferably 5.0 to 6.0, and more preferably 5.0 to 5.5. If the pH is less than 5.0, cobalt ions may not be sufficiently extracted into the solvent. As the pH adjusting agent at this time, it is preferable to use an aqueous lithium hydroxide solution obtained in the electrodialysis step as described later.

In the extraction of the cobalt ions as well, it is desirable to carry out the extraction by countercurrent type multistage extraction in which directions of flow of the aqueous phase and the solvent used for each extraction are opposite to each other. By doing so, it is possible to increase an extraction rate of cobalt ions while suppressing the extraction of nickel ions and lithium ions. However, if the extraction is performed in multiple stages, the number of contacts of the extracting agent with the metal-containing solution increases, so that the amount of phosphorus derived from the phosphoric acid-based extracting agent mixed into the metal-containing solution may increase.

During the above extraction, not only cobalt ions but also nickel ions and lithium ions may be somewhat extracted into the solvent. In this case, if necessary, the solvent which has extracted the cobalt ions may be subjected to one or more scrubbing processes 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 can have a pH of 3.5 to 5.5. The scrubbed solution may contain nickel ions and lithium ions. Therefore, a part or all of the scrubbed solution is mixed with the manganese extracted solution and it is used as an extracting solution to be subjected to the extraction of the cobalt ions. As a result, the nickel ions and lithium ions can be circulated or retained in the wet processes without losing them. However, the scrubbed solution may contain large amounts of fluoride ions and phosphorus. When such a scrubbed solution is mixed with the extracting solution and circulated, the fluoride ions and phosphorus removed from the solvent by scrubbing are returned to the metal-containing solution, which may tend to leave fluoride ions and phosphorus until the electrodialysis step. In addition, if the solvent used to extract the cobalt ions does not contain nickel ions or lithium ions, the scrubbing step may not be performed.

The solvent which has extracted the cobalt ions is then subjected to stripping. A stripping solution used for the stripping may be any inorganic acid such as sulfuric acid, hydrochloric acid, and nitric acid, but sulfuric acid is preferable when a sulfate is obtained in the next crystallization. Here, it is carried out under pH conditions such that all the cobalt ions transfer from the solvent to the stripping solution as much as possible. More particularly, 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.

The stripped solution can be subjected to crystallization. Here, the stripped solution is heated to, for example, 40°C to 120°C and concentrated. As a result, the cobalt ions are crystallized to obtain a cobalt salt such as cobalt sulfate. The cobalt salt thus obtained preferably has a nickel content of 5 ppm by mass or less, and have sufficiently removed the nickel, so that it can be effectively used as a raw material for producing lithium ion secondary batteries and other batteries. Here, the crystallized solution may contain uncrystallized cobalt ions and lithium ions. Therefore, it is preferable that the crystallized solution is mixed with the stripped solution before the crystallization and used for recrystallization, or used for adjusting the cobalt ion concentration of the scrubbing solution used for the solvent which has extracted the cobalt ions, or mixed with the manganese extracted solution and used for the extraction of the cobalt ions. By doing so, the cobalt ions and lithium ions can be circulated or retained and concentrated in the wet processes without losing them.

(Nickel Extraction and Crystallization)
The cobalt extracted solution (metal-containing solution) after the cobalt ions have been extracted can be subjected to solvent extraction to extract nickel ions.

In the extraction of nickel, a carboxylic acid-based extracting agent is preferably used to separate nickel ions from the cobalt extracted solution. Examples of the carboxylic acid-based extracting agent include neodecanoic acid and naphthenic acid. Among them, the neodecanoic acid is preferred because of its ability to extract nickel ions. The extracting agent may be diluted with an aromatic, paraffinic, naphthenic, or other hydrocarbon organic solvent to a concentration of 10% to 30% by volume and used as a solvent.

The equilibrium pH during the extraction is preferably 6.0 to 8.0, and more preferably 6.8 to 7.2. The pH adjusting agent used to adjust the pH at this time is preferably an aqueous lithium hydroxide solution obtained in an electrodialysis step as described below. In the extraction of the nickel ions, it is desirable to perform the countercurrent type multistage extraction. By doing so, the extraction of lithium ions can be suppressed, and the extraction rate of nickel ions can be increased.

The solvent which has extracted the nickel ions may optionally be subjected to one or more scrubbing processes using a scrubbing solution to remove lithium ions that may be contained in the solvent. The scrubbing solution can be, for example, a sulfuric acid solution and can have a pH of 5.0 to 6.0. Here, the resulting scrubbed solution may contain lithium ions. Therefore, it is preferable that a part or all of the scrubbed solution is mixed with the cobalt extracted solution and it is used as the extracting solution to be subjected to the extraction of the nickel ions. As a result, the lithium ions can be circulated or retained and concentrated in the wet processes without losing them. However, if the solvent used to extract the nickel ions does not contain lithium ions, the scrubbing may not be performed.

The solvent is then subjected to stripping using a stripping solution such as sulfuric acid, hydrochloric acid, or nitric acid. The sulfuric acid is particularly preferred if crystallization is then performed. The pH is preferably in the range of 1.0 to 3.0, and more preferably 1.5 to 2.5. Although the O/A ratio and the number of times can be determined as needed, the O/A ratio is 5 to 1, and more preferably 4 to 2.

When the extracted solution such as a nickel sulfate solution is obtained by the stripping, electrolysis and dissolution can be carried out as needed, and the solution can be then heated to 40°C to 120°C in the crystallization to crystalize the nickel ions as a nickel salt such as nickel sulfate. This provides the nickel salt. Here, the crystallized solution may contain uncrystallized nickel ions and lithium ions. Therefore, the crystallized solution is mixed with the stripped solution before the crystallization and used for recrystallization, or used for adjusting the nickel ion concentration of the scrubbing solution with respect to the solvent which has extracted the nickel ions, or mixed with the cobalt extracted solution and used for the extraction of the nickel ions. By repeatedly using them in the steps in this manner, the nickel ions and lithium ions can be circulated or retained and concentrated in the wet processes without losing them.

The nickel extracted solution from which the nickel ions have been extracted mainly contains lithium ions and may be added to the acidic leaching solution in the leaching step. This allows the lithium ions contained in the nickel extracted solution to be circulated in a series of steps from the acid leaching step to the nickel extraction. Preferably, after the lithium ion concentration in the nickel extracted solution has been increased to some extent by thus circulating the lithium ions, an electrodialysis step as described below can be carried out.

(Electrodialysis Step)
The metal-containing solution such as the extracted nickel solution obtained in the metal separation step described above is one in which lithium ions and metals other than impurities are sufficiently separated, and mainly contains lithium ions.

The metal-containing solution contains fluoride ions (F^-) as impurities derived from, for example, the electrolytic solution contained in the battery powder. The impurities may also include phosphorus (P). The Phosphorus, in particular, tends to be contained, which is derived from the contamination of the phosphoric acid-based extractant used upon multiple solvent extraction processes such as manganese extraction and cobalt extraction in the liquid. Further, as described above, when the phosphate ion source is added in order to sufficiently separate the aluminum ions in the aluminum removal stage of the neutralization step, the metal-containing solution may contain a relatively large amount of phosphorus as an impurity. Other impurities may include silicon derived from, for example, glass fibers in the lithium ion battery waste.

The metal-containing solution may contain trace amounts of cations such as nickel ions and magnesium ions that could not be completely separated in the metal separation step. The nickel ions and magnesium ions are cations like lithium ions, and exhibit the same behavior as lithium ions during electrodialysis, so that it is difficult to separate them from lithium ions. Also, when the electrodialysis is performed on the metal-containing solution containing the nickel ions and magnesium ions, hydroxides of nickel and magnesium may be generated in the resulting lithium hydroxide solution, and the electrodialysis cannot be continued due to troubles of the steps. Therefore, in such a case, it is desirable to wash the metal-containing solution to remove cations such as nickel ions and magnesium ions prior to the electrodialysis which will be described below. The washing can be carried out using an ion exchange resin or a chelate resin, for example.

The metal-containing solution prior to the electrodialysis step may, for example, have 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.

When a lithium hydroxide solution is obtained from the above metal-containing solution, application of carbonation, chemical conversion, or the like causes impurities to remain in the lithium hydroxide solution without being removed. The use of the lithium hydroxide solution containing larger amounts of impurities as a pH adjusting agent in the metal separation step is undesirable because not only lithium ions but also impurities are circulated or accumulated in the wet processes.

Therefore, in this embodiment, the metal-containing solution is subjected to the electrodialysis step 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, it is possible to obtain the lithium hydroxide solution from which the impurities have been sufficiently removed.

The electrodialysis step can be performed, for example, using a commercially available bipolar membrane electrodialysis device. As an example, a bipolar membrane electrodialysis device 1 (hereinafter, also referred to as a “electrodialysis device”) shown in Fig.3 has, in a cell, a positive electrode 2 and a negative electrode 3; and a bipolar membrane 4, an anion exchange membrane 5, a cation exchange membrane 6, and a bipolar membrane 7, which are arranged in this order between the positive electrode 2 and the negative electrode 3 from the positive electrode 2 side to the negative electrode 3 side. These separate the interior of the cell into a desalination chamber R1 between the anion exchange membrane 5 and the cation exchange membrane 6, an acidic chamber R2 between the bipolar membrane 4 and the anion exchange membrane 5, and an alkaline chamber R3a between the cation exchange membrane 6 and the bipolar membrane 7. Each of the

bipolar membranes

4 and 7 is constructed by laminating a cation exchange layer and an anion exchange layer.

In order to carry out electrodialysis by the illustrated electrodialysis device 1, the metal-containing solution is placed in the desalination chamber R1, and pure water is also placed in each of the acidic chamber R2 and the alkaline chamber R3, and a predetermined voltage is applied to the positive electrode 2 and the negative electrode 3. Then, lithium ions (Li⁺) in the metal-containing solution in the desalination chamber R1 pass through the cation exchange membrane 6 and move to the alkaline chamber R3. In the alkaline chamber R3, water (H₂O) is decomposed by the bipolar membrane 7 and hydroxide ions (OH^-) are present, so that a lithium hydroxide solution is obtained.

On the other hand, the anions of the inorganic acid in the metal-containing solution in the desalination chamber R1 pass through the anion exchange membrane 5 and move to the acidic chamber R2. In the acidic chamber R2, an acidic solution such as a sulfuric acid solution is generated by the anions and hydrogen ions (H⁺) generated from water (H₂O) by the bipolar membrane 4. As a result, the lithium hydroxide solution obtained in the alkaline chamber R3 contains substantially no inorganic acid anions. It should be noted that the anions of the inorganic acid are sulfate ions (SO₄ ^2-) in the illustrated example, but they may be nitrate ions (NO₃ ^-) or chloride ions (Cl^-) depending on the type of the acid used in the acid leaching step.

In the desalination chamber R1, the lithium salt is separated from the metal-containing solution as described above, and a desalinated solution remains. The anion concentration of the inorganic acid tends to be higher in the acidic solution than in the lithium hydroxide solution, and tends to be higher in the desalinated solution than in the lithium hydroxide solution.

In the electrodialysis, most of the impurity fluoride ions in the metal-containing solution move from the desalination chamber R1 to the acidic chamber R2 through the anion exchange membrane 5 and are contained in the acidic solution. The silicon as an impurity can also migrate into the acidic solution. As a result, a lithium hydroxide solution substantially free of fluoride ions and silicon is obtained in the alkaline chamber R3. Therefore, the fluoride ion concentration of the lithium hydroxide solution is lower than that of the acidic solution.

Moreover, it was found that most of the phosphorus as an impurity in the metal-containing solution remained in the desalination chamber R1 without passing through both the cation exchange membrane 6 and the anion exchange membrane 5. Therefore, the lithium hydroxide solution obtained by electrodialysis contains substantially no phosphorus. Therefore, the phosphorus concentration of the desalinated solution remaining in the desalination chamber R1 after the lithium salt is separated from the metal-containing solution is higher than the phosphorus concentration of the lithium hydroxide solution.

The lithium hydroxide solution from which impurities have been removed by electrodialysis as described above can be effectively used as a pH adjusting agent in the metal separation step. After the electrodialysis, the lithium hydroxide solution may optionally be used as a pH adjusting agent after increasing the lithium ion concentration of the lithium hydroxide solution by heat concentration or the like.

(Crystallizing Step)
A part of the lithium hydroxide solution obtained in the electrodialysis step can be subjected to a crystallizing step. For example, when the lithium hydroxide solution is returned to the wet process as a pH adjusting agent as described above, the lithium in the battery powder newly added to the wet process may gradually increase the lithium ion concentration in the liquid. Depending on the lithium ion concentration, the crystallizing step may be performed to recover lithium hydroxide.

In the crystallizing step, a crystallizing operation such as heat concentration or vacuum distillation can be performed in order to crystallize lithium hydroxide. For the heat concentration, a higher temperature during crystallizing leads to faster progression of the process, which is preferable. However, the temperature of the crystallized product after crystallizing can be a temperature of less than 60°C at which water in the crystallized product is not released. This is because anhydrous lithium hydroxide from which the water has been released is deliquescent and thus difficult to be handled.

As described above, the lithium hydroxide solution obtained in the electrodialysis step contains substantially no inorganic acid anions such as sulfate ions. Therefore, the lithium hydroxide produced in the crystallization step will have higher purity and improved quality.

In addition, a pulverization process or the like can be then performed in order to adjust the above lithium hydroxide to required physical properties.

Next, the method for removing impurities as described above was experimentally carried out and the effects thereof were confirmed, as described below. However, the descriptions herein are merely for illustrative and are not intended to be limited.

The metal-containing solution obtained by leaching the battery powder with sulfuric acid was subjected to neutralization, manganese extraction, cobalt extraction and nickel extraction to separate each metal.

The separated metal-containing solution was then subjected to electrodialysis using a bipolar membrane electrodialysis device (manufactured by ASTOM Corporation) having a structure as shown in Fig. 3. Here, the metal-containing solution having each composition shown in Fig. 4, pure water, and an electrode solution were introduced into the desalination chamber, the alkaline chamber, the acidic chamber, and the electrode chamber, respectively. The electrodialysis was carried out under the condition of a constant voltage of 32V.

The results are also shown in Fig 4. In Fig. 4, the reason why the distribution ratios of the ions in the desalinated solution after electrodialysis, the lithium hydroxide solution, the acidic solution, and the electrode solution do not reach 100% even if the respective distribution ratios are added up would be because of the variation in analytical values (it does not include those which could not be quantified due to the lower limit of analysis, or the like).

It is found from Fig. 4 that the fluoride ion concentration, the phosphorus concentration and the silicon concentration in the lithium hydroxide solution obtained after electrodialysis are all sufficiently low. This indicates that the electrodialysis provides a lithium hydroxide solution from which most of the impurities have been removed.

It was found from the foregoing that impurities such as fluoride ions can be effectively removed by the method for removing impurities described above.

Description of Reference Numerals

1. bipolar membrane electrodialysis device
2 positive electrode
3 negative electrode
4, 7 bipolar membrane
5 anion exchange membrane
6 cation exchange membrane
R1 desalination chamber
R2 Acidic chamber
R3 alkaline chamber

Claims

A method for removing impurities from a metal-containing solution obtained by leaching battery powder of 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 the other metal ions; and,
after the metal separation step, an electrodialysis step of subjecting the metal-containing solution containing lithium ions, and fluoride ions as impurities, to electrodialysis using a bipolar membrane to obtain a lithium hydroxide solution and an acidic solution,
wherein the lithium hydroxide solution is used as a pH adjusting agent in the metal separation step.
The method for removing impurities according to claim 1, wherein a fluoride ion concentration of the lithium hydroxide solution is lower than that of the acidic solution.
The method for removing impurities according to claim 1,
wherein the metal separation step comprises separating the other metal ions from the metal-containing solution by solvent extraction, and
wherein the lithium hydroxide solution is used as a pH adjusting agent in the solvent extraction.
The method for removing impurities according to claim 3,
wherein the metal-containing solution comprises a plurality of types of the other metal ions, and
wherein, in the metal separation step, the solvent extraction is performed multiple times depending on the types of the other metal ions.
The method for removing impurities according to claim 3,
wherein the other metal ions comprise cobalt ions and/or nickel ions; and
wherein, in the metal separation step, the cobalt ions and/or the nickel ions are separated from the metal-containing solution by solvent extraction.
The method for removing impurities according to claim 3,
wherein the other metal ions comprise manganese ions and/or aluminum ions; and
wherein, in the metal separation step, the manganese ions and/or the aluminum ions are separated from the metal-containing solution by solvent extraction.
The method for removing impurities according to claim 3,
wherein, in the metal separation step, a phosphoric acid-based extracting agent is used for the solvent extraction, and
wherein the impurities contained in the metal-containing solution further comprise phosphorus.
The method for removing impurities according to claim 7, wherein a concentration of phosphorus in a desalinated solution obtained by separating a lithium salt from the metal-containing solution in the electrodialysis step is higher than that of phosphorus in the lithium hydroxide solution.
The method for removing impurities according to claim 1,
wherein the other metal ions comprise aluminum ions and/or iron ions, and
wherein, in the metal separation step, the aluminum ions and/or the iron ions are separated from the metal-containing solution by neutralization, and the lithium hydroxide solution is used as a pH adjusting agent for the neutralization.
The method for removing impurities according to claim 1,
wherein the other metal ions comprise aluminum ions, and the neutralization step comprises an aluminum removal stage,
wherein a phosphate ion source is added during a period to an end of the aluminum removal stage, and phosphate ions are present in the metal-containing solution, and
wherein, in the aluminum removal step, the aluminum ions and the phosphate ions in the metal-containing solution are allowed to react with each other to separate the aluminum ions from the metal-containing solution.
A method for recovering metals from battery powder of lithium ion battery waste, the method comprising using the method for removing impurities according to any one of claims 1 to 9.