Method for removing impurities and method for recovering metals

Abstract

The present invention provides an impurity removal method and a metal recovery method that can effectively remove impurities such as fluoride ions. [Solution] A method for removing impurities from a metal-containing solution obtained by leaching battery powder from lithium-ion battery waste with acid, comprising: a metal separation step of separating other metal ions from the metal-containing solution which contains lithium ions and other metal ions; and an electrodialysis step of performing electrodialysis using a bipolar membrane on the metal-containing solution which contains fluoride ions as impurities after the metal separation step 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, recovering valuable metals such as cobalt and nickel contained in lithium-ion battery waste discarded due to product lifespan or manufacturing defects or other reasons has been widely studied from the perspective of effective utilization of resources.

[0003] The process of 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] ​​​​​​​​​​​​Incidentally, pH adjusters are used to raise and adjust the pH during the neutralization and solvent extraction processes described above. While it is possible to prepare and use sodium hydroxide or other pH adjusters separately, it is preferable 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 suppresses contamination from sodium and other substances derived from separately prepared pH adjusters and reduces the cost associated with such pH adjusters.

[0007] However, metal-containing solutions contain 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 as a pH adjuster, there is a concern that the aforementioned impurities will accumulate and become concentrated, affecting the process.

[0008] This specification provides an impurity removal method and a metal recovery method that can effectively remove impurities such as fluoride ions. [Means for solving the problem]

[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 acid, comprising: a metal separation step of separating other metal ions from the metal-containing solution which contains lithium ions and other metal ions; and an electrodialysis step of performing electrodialysis using a bipolar membrane on the metal-containing solution which contains lithium ions and fluoride ions of impurities after the metal separation step 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.

[0010] Furthermore, the metal recovery method disclosed in this specification is a method for recovering metal from battery powder, which is a waste product of lithium-ion batteries, and uses the impurity removal method described above. [Effects of the Invention]

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

[0012] [Figure 1] This is a flowchart showing an example of a metal recovery method that includes an impurity removal method according to one embodiment. [Figure 2] This is a flowchart illustrating an example of a pretreatment process for obtaining battery powder from lithium-ion battery waste. [Figure 3] This is a schematic cross-sectional view showing an example of a bipolar membrane electrodialysis apparatus that can be used in the electrodialysis process included in one embodiment of the impurity removal method. [Figure 4] This figure shows the components of each solution before and after electrodialysis in the example. [Modes for carrying out the invention]

[0013] The embodiments of the impurity removal method and metal recovery method described above will be explained in detail below. One embodiment of the impurity removal method involves removing impurities from a metal-containing solution obtained by leaching battery powder from lithium-ion battery waste with acid. This method includes a metal separation step for separating other metal ions from a metal-containing solution containing lithium ions and other metal ions, and an electrodialysis step in which, after separating the other metal ions in the metal separation step, electrodialysis is performed using a bipolar membrane on the metal-containing solution containing lithium ions and impurity fluoride ions 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] In the electrodialysis process, most of the fluoride ions contained in the metal-containing solution migrate to the acidic solution and are effectively removed, as they are almost entirely absent from the lithium hydroxide solution. Therefore, when the lithium hydroxide solution is used as a pH adjuster in the metal separation process and circulated within the wet treatment of the metal recovery method, the accumulation and concentration of fluoride ions can be suppressed. Furthermore, inorganic acid anions such as sulfate, nitrate, and chloride ions also migrate to the acidic solution and are almost entirely absent from the lithium hydroxide solution, resulting in a high-purity lithium hydroxide solution. This significantly contributes to improving the quality of lithium hydroxide.

[0015] In the metal recovery method of the embodiment described herein, as illustrated in Figure 1, a wet treatment is performed, which includes an acid leaching step in which the battery powder of lithium-ion battery waste is leached with acid to obtain a metal-containing solution, and the above-mentioned metal separation step and electrodialysis step. The lithium hydroxide solution obtained in the electrodialysis step is concentrated as needed and then used as a pH adjuster in the metal separation step. In Figure 1, the metal separation step includes neutralization, solvent extraction of manganese ions and / or aluminum ions (Mn extraction, 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, neutralization and at least one of the multiple solvent extractions may be omitted.

[0016] (Lithium-ion battery waste) The lithium-ion battery waste targeted is lithium-ion secondary batteries that can be used in mobile phones and various other electronic devices, and which are discarded due to the battery product's lifespan, manufacturing defects, or other reasons. Recovering valuable metals from such lithium-ion battery waste is desirable from the standpoint of effective resource utilization.

[0017] Lithium-ion battery waste has an outer casing containing aluminum that encloses the lithium-ion secondary battery. This casing may consist of aluminum alone, or it may contain aluminum and iron, aluminum laminate, etc.

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

[0019] Furthermore, the housing of lithium-ion battery waste usually contains an electrolytic 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 lithium-ion battery waste. The pretreatment process may include at least one of roasting, crushing, and sieving. Lithium-ion battery waste becomes battery powder through the pretreatment process. Roasting, crushing, and sieving in the pretreatment process may be performed as needed respectively, or may be performed in any order. In the example shown in FIG. 2, roasting, crushing, and sieving are performed in this order.

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

[0022] In roasting, the lithium-ion battery waste described above is heated. Roasting can change metals such as lithium and cobalt contained in the lithium-ion battery waste into a form that is easily soluble. During roasting, it is preferable to heat the lithium-ion battery waste by holding it at a temperature range of, for example, 450°C to 1000°C, and then 600°C to 800°C for 0.5 to 4 hours. Roasting can be carried out in an air atmosphere or an inert atmosphere such as nitrogen, or both air and inert atmospheres may be used in that order or in the reverse order. The roasting furnace may be batch type or continuous type; for example, a stationary furnace can be used for batch type, a rotary kiln furnace for continuous type, and various other types of furnaces can also be used.

[0023] During roasting, at least a portion of the electrolyte is removed from lithium-ion battery waste due to evaporation. In most cases, when lithium-ion battery waste is heated during roasting, components with lower boiling points in the internal electrolyte evaporate sequentially. Furthermore, when the lithium-ion battery waste reaches even higher temperatures, resins such as organic binders decompose or vaporize. Even if some of the electrolyte and organic binder are removed in this way, certain components such as fluorine that were contained in the electrolyte and organic binder remain and may 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 aluminum foil and positive electrode active material during the crushing and sieving processes described later. Note that the composition of the positive electrode active material changes due to roasting, but here it will be referred to as positive electrode active material even after roasting.

[0024] After roasting, crushing can be performed to extract positive electrode active material and other components from the lithium-ion battery waste casing. Crushing destroys the lithium-ion battery waste casing and selectively separates the positive electrode active material from the aluminum foil coated with it.

[0025] Various known devices or equipment can be used for crushing, but it is particularly preferable to use an impact-type crusher that can crush lithium-ion battery waste by applying impact while cutting it. Examples of such impact-type crushers include sample mills, hammer mills, pin mills, wing mills, tornado mills, and hammer crushers. A screen can be installed at the outlet of the crusher, so that the lithium-ion battery waste is crushed to a size that can pass through the screen and then discharged from the crusher through the screen.

[0026] After crushing the lithium-ion battery waste, sieving is performed using a sieve with an appropriate mesh size. This allows for obtaining battery powder with aluminum and copper remaining on the sieve surface, and aluminum and copper removed to some extent on the underside.

[0027] The battery powder obtained in the pretreatment 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 fluorine in an amount of 0.1% to 10% by mass.

[0028] The battery powder can be brought into contact with water before the acid leaching process described later, in order to extract essentially only lithium from it. This causes the lithium in the battery powder to leach into the water. In this case, the battery powder as a residue after water leaching is then subjected to the acid leaching process. However, if water leaching is performed, equipment is required, and the processing time increases due to performing both water leaching and the acid leaching process. Furthermore, it may be necessary to control conditions such as roasting to effectively leach lithium with water. Even with such control, it may not be possible to significantly increase the lithium leaching rate with water. Therefore, the battery powder obtained as described above may be subjected to the acid leaching process without water leaching. If water leaching is not performed, it becomes easier to maintain a high lithium ion concentration in the liquid during the wet processing after the acid leaching process.

[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 to leach out the lithium and other metals contained in the lithium-ion battery waste.

[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, based on silver / silver chloride potential) may be 0 mV or less.

[0031] The leaching residue remaining after acid leaching can be separated from the metal-containing solution by solid-liquid separation, such as filtration using known devices and methods such as filter presses and thickeners. Much of the copper in the battery powder can sometimes be contained within the leaching residue. This solid-liquid separation is optional, and metal separation steps such as neutralization may be performed after leaching without solid-liquid separation.

[0032] The acid leaching process yields a metal-containing solution containing lithium ions and other metal ions. These 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 include cobalt ions and / or nickel ions. The metal-containing solution may also contain fluoride ions.

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

[0034] (neutralization) If the metal-containing solution obtained in the acid leaching process contains aluminum ions and / or iron ions, the metal separation process may first involve raising the pH of the metal-containing solution and separating the neutralization residue to obtain the neutralized solution. Neutralization may include a dealuminizing step and a deiraging step. However, if the metal-containing solution does not contain aluminum ions and / or iron ions, the dealuminizing step and / or deiraging step may be omitted.

[0035] In the dealuminization stage, at least some of the aluminum ions are precipitated by increasing the pH of the metal-containing solution and then removed by solid-liquid separation. At this time, for example, if the pH is raised to 2.5 to 5.0, particularly within the range of 3.0 to 4.5, using a pH adjusting agent at a liquid temperature of 50°C to 90°C, aluminum ions can be effectively separated while suppressing the precipitation of nickel ions and / or cobalt ions.

[0036] It is preferable to add a phosphate ion source before the dealuminization step is completed. This allows aluminum ions in the metal-containing solution to react with phosphate ions during the dealuminization step, causing the aluminum ions to precipitate as aluminum phosphate, which can then be removed by solid-liquid separation. The timing of adding the phosphate ion source is not particularly important. If phosphate ions are present in the metal-containing solution during the dealuminization step, the above reaction will occur. Examples of phosphate ion sources include phosphoric acid (H3PO4).

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

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

[0039] (Manganese extraction process) After neutralization as necessary, the metal-containing solution can be extracted and removed from the solution by solvent extraction to remove manganese ions. In this case, if the metal-containing solution also contains aluminum ions, not only manganese ions but also aluminum ions will be extracted and removed.

[0040] For the extraction of manganese ions, it is preferable to use an extractant containing a phosphate-based extractant, or more specifically, a phosphate ester-based extractant. A specific example of a phosphate ester-based extractant is di-2-ethylhexyl phosphate (abbreviation: D2EHPA or trade name: DP8R). When a phosphate-based extractant is used, phosphorus tends to be present as an impurity in the metal-containing solution obtained as a post-extract solution after manganese extraction, and further in the metal-containing solution that undergoes the subsequent electrodialysis process.

[0041] Furthermore, the extractant may be a mixture of a phosphate ester extractant and an oxime extractant. In this case, the oxime extractant is preferably one in which aldoxime or aldoxime is the main component. Specifically, examples include 2-hydroxy-5-nonylacetophenone oxime (trade name: LIX84), 5-dodecylsalicylaldoxime (trade name: LIX860), a mixture of LIX84 and LIX860 (trade name: LIX984), and 5-nonylsalicylaldoxime (trade name: ACORGAM5640).

[0042] The extractant may be diluted with a hydrocarbon-based organic solvent such as aromatic, paraffinic, or naphthenic solvent to a concentration of 10% to 30% by volume, and this diluted solvent may be used as the solvent.

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

[0044] For extraction, it is desirable to use a counter-flow multi-stage extraction method in which the flow directions of the aqueous phase and solvent used in each extraction are reversed. This suppresses the extraction of cobalt ions, nickel ions, and lithium ions, while increasing the extraction rate of manganese ions. When using a counter-flow multi-stage extraction method, it is effective to set the equilibrium pH during the first extraction stage to a value within the above range, and then lower the equilibrium pH during extraction with each subsequent stage. However, if multiple stages of extraction are used, the number of contacts between the extractant and the metal-containing solution increases, which may increase the amount of phosphorus from the phosphate-based extractant mixed into the metal-containing solution.

[0045] Since the solvent from which manganese ions have been extracted may contain cobalt ions, nickel ions, and lithium ions, these ions that may be present 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, with a pH of 2.0 to 3.0. The back-extract solution can be, for example, a sulfuric acid solution, with a pH of 0.0 to 1.0. It is desirable to use the scrubbing solution, back-extraction solution, and scavenging solution in the manganese extraction process (for example, mixing the scrubbing solution with a metal-containing solution and using it as a pre-extraction solution for solvent extraction in the manganese extraction process, using the back-extraction solution for scrubbing in the manganese extraction process, or using the scavenging solution as a back-extract solution in the manganese extraction process). This allows cobalt ions, nickel ions, and lithium ions to be circulated or retained within the process without loss. However, the scrubbing solution in particular may contain a large amount of fluoride ions and phosphorus. When such a scrubbing solution is mixed with the pre-extraction solution and circulated, fluoride ions and phosphorus removed from the solvent by scrubbing are returned to the metal-containing solution, which can make it easier for fluoride ions and phosphorus to remain until the electrodialysis process. Note that if the solvent from which manganese ions were extracted does not contain cobalt ions, nickel ions, or lithium ions, scrubbing, back-extraction, or scavenging may not be necessary.

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

[0047] For the extraction of cobalt ions, it is preferable to use a solvent containing a phosphate-based extractant, particularly a phosphonic acid ester extractant. In particular, 2-ethylhexyl 2-ethylhexylphosphonate (trade names: PC-88A, Ionquest801) is preferred from the viewpoint of nickel-cobalt separation efficiency. The extractant can be diluted with a hydrocarbon-based organic solvent to a concentration of 10% to 30% by volume and used as a solvent. However, when a phosphate-based extractant is used, phosphorus is more likely to be present as an impurity in the metal-containing solution obtained after cobalt extraction, and in the metal-containing solution subjected to subsequent electrodialysis.

[0048] When extracting cobalt ions, the equilibrium pH during extraction should preferably be 5.0 to 6.0, more preferably 5.0 to 5.5. If the pH is lower than 5.0, there is a risk that the cobalt ions may not be sufficiently extracted into the solvent. In this case, it is preferable to use an aqueous lithium hydroxide solution obtained in the electrodialysis process described later as the pH adjusting agent.

[0049] When extracting cobalt ions, it is desirable to use a counter-flow multi-stage extraction method in which the flow directions of the aqueous phase and solvent used in each extraction are reversed. This method suppresses the extraction of nickel ions and lithium ions while increasing the extraction rate of cobalt ions. However, since multiple extraction stages increase the number of contacts between the extractant and the metal-containing solution, the amount of phosphorus from the phosphate-based extractant mixed into the metal-containing solution may increase.

[0050] During the extraction process described above, not only cobalt ions but also small amounts of nickel 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 once or more times using a scrubbing solution to remove any nickel and lithium ions that may be present in the solvent. The scrubbing solution can be, for example, a sulfuric acid solution, with a pH of 3.5 to 5.5. The scrubbed solution may contain nickel and lithium ions. Therefore, it is desirable to mix part or all of the scrubbed solution with the manganese extraction solution and use this as the pre-extraction solution for cobalt ion extraction. This allows nickel and lithium ions to be circulated or retained within the wet process without loss. However, the scrubbed solution may contain a large amount of fluoride ions and phosphorus. If such a scrubbed solution is mixed with the pre-extraction solution and circulated, the fluoride ions and phosphorus removed from the solvent by scrubbing are returned to the metal-containing solution, which may cause fluoride ions and phosphorus to remain in the electrodialysis process. Furthermore, if the solvent from which the cobalt ions were extracted does not contain nickel ions or lithium ions, the scrubbing step may not be necessary.

[0051] Subsequently, back-extraction is performed on the solvent from which the cobalt ions were extracted. Any inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid can be used as the back-extract solution, but sulfuric acid is preferable if sulfates are to be obtained in the subsequent crystallization. Here, the pH conditions should be such that as many cobalt ions as possible are transferred from the solvent to the back-extract solution. Specifically, the pH is preferably in the range of 2.0 to 4.0, and more preferably in the range of 2.5 to 3.5.

[0052] Crystallization can be performed on the back-extracted solution. Here, the back-extracted solution is concentrated by heating it to, for example, 40°C to 120°C. This causes the cobalt ions to crystallize, yielding cobalt salts such as cobalt sulfate. The cobalt salts obtained in this way have a nickel content of preferably 5 ppm by mass or less, and since the nickel has been sufficiently removed, they can be effectively used as raw materials for the manufacture of lithium-ion secondary batteries and other batteries. However, the crystallized solution may contain cobalt ions and lithium ions that did not crystallize. Therefore, it is desirable to mix the crystallized solution with the back-extracted solution before crystallization for further crystallization, to use it to adjust the cobalt ion concentration of the scrubbing solution used as the solvent for extracting cobalt ions, or to mix it with the manganese extract solution for extracting cobalt ions. In this way, cobalt ions and lithium ions can be circulated or retained within the wet process and concentrated without loss.

[0053] (Nickel extraction and crystallization) Nickel ions can be extracted from the cobalt extract solution (metal-containing solution) remaining after the extraction of cobalt ions by solvent extraction.

[0054] In the extraction of nickel ions, a carboxylic acid-based extractant is preferably used to separate the nickel ions from the cobalt extract. Examples of carboxylic acid-based extractants include neodecanoic acid and naphthenic acid, but neodecanoic acid is preferred due to its ability to extract nickel ions. The extractant may be diluted with a hydrocarbon-based organic solvent such as an aromatic, paraffinic, or naphthenic solvent to a concentration of 10% to 30% by volume 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. For pH adjustment at this time, it is preferable to use an aqueous lithium hydroxide solution obtained in the electrodialysis process described later. When extracting nickel ions, it is desirable to perform a countercurrent multi-stage extraction. This suppresses the extraction of lithium ions and increases the extraction rate of nickel ions.

[0056] For the solvent from which nickel ions were extracted, scrubbing may be performed one or more times using a scrubbing solution to remove any lithium ions that may be present in the solvent, if necessary. The scrubbing solution can be, for example, a sulfuric acid solution, and its pH can be set to 5.0 to 6.0. Here, the post-scrubbing solution may contain lithium ions. Therefore, it is desirable to mix part or all of the post-scrubbing solution with the post-cobalt extraction solution and use this as the pre-extraction solution for nickel ion extraction. This allows for the concentration of lithium ions by circulation or retention within the wet process without loss. However, if the solvent from which nickel ions were extracted does not contain lithium ions, scrubbing may not be necessary.

[0057] Subsequently, back-extraction is performed using a back-extract solution such as sulfuric acid, hydrochloric acid, or nitric acid in the solvent. If crystallization is performed afterward, sulfuric acid is preferred. The pH is preferably in the range of 1.0 to 3.0, and more preferably 1.5 to 2.5. The O / A ratio and the number of passes can be determined as appropriate, but the O / A ratio is 5 to 1, more preferably 4 to 2.

[0058] When a back-extraction solution such as nickel sulfate solution is obtained by back-extraction, electrolysis and dissolution can be performed as needed, and then the solution can be heated to 40°C to 120°C for crystallization, allowing nickel ions to crystallize as nickel salts such as nickel sulfate. This yields nickel salts. However, the crystallized solution may contain uncrystallized nickel ions and lithium ions. Therefore, it is desirable to mix the crystallized solution with the back-extraction solution before crystallization for further crystallization, to use it to adjust the nickel ion concentration of the scrubbing solution relative to the solvent from which nickel ions were extracted, or to mix it with the cobalt extract solution for nickel ion extraction. By repeatedly using the solution in this way within the process, nickel ions and lithium ions can be circulated or retained within the wet process and concentrated without loss.

[0059] The nickel extract solution, after nickel ions have been extracted, mainly contains lithium ions and may be added to the acid leachate in the acid leaching process. This allows the lithium ions contained in the nickel extract solution to be circulated throughout the series of processes from acid leaching to nickel extraction. Preferably, after the lithium ion concentration in the nickel extract solution has increased to a certain extent by circulating the lithium ions in this way, the electrodialysis process described below can be carried out.

[0060] (Electrodialysis process) The metal-containing solutions obtained in the metal separation process described above, such as the nickel extract solution, are those in which metals other than lithium ions and impurities have been sufficiently separated, and mainly contain lithium ions.

[0061] Metal-containing solutions may contain impurities such as fluoride ions (F) originating from the electrolyte contained in battery powder. -) are included. Furthermore, impurities may include phosphorus (P). Phosphorus tends to be present, in particular, when multiple solvent extractions such as manganese extraction or cobalt extraction are performed, as the phosphate-based extractants used at that time become mixed into the solution. Also, as mentioned above, when a phosphate ion source is added in order to sufficiently separate aluminum ions at the dealuminization stage of the neutralization process, the metal-containing solution may contain a certain amount of phosphorus as an impurity. Other impurities may include silicon, for example, derived from glass fibers in lithium-ion battery waste.

[0062] Furthermore, metal-containing solutions may contain trace amounts of cations such as nickel and magnesium ions that were not completely separated during the metal separation process. Nickel and magnesium ions are cations, just like lithium ions, and exhibit similar behavior during electrodialysis, making them difficult to separate from lithium ions. In addition, performing electrodialysis on a metal-containing solution containing nickel and magnesium ions may generate nickel and magnesium hydroxides in the resulting lithium hydroxide solution, raising concerns that electrodialysis may become impossible due to process problems. For this reason, in such cases, it is desirable to wash the metal-containing solution to remove cations such as nickel and magnesium ions prior to the electrodialysis described below. For example, ion exchange resins or chelate resins can be used for this washing.

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

[0064] When obtaining a lithium hydroxide solution from the above-mentioned metal-containing solution, applying carbonation and chemical conversion methods may result in impurities remaining in the lithium hydroxide solution without being removed. Using a lithium hydroxide solution containing many impurities as a pH adjuster in the metal separation process is undesirable because not only lithium ions but also impurities will circulate or accumulate within the wet treatment process.

[0065] Therefore, in this embodiment, an electrodialysis process 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 sufficiently removed impurities can be obtained.

[0066] The electrodialysis process can be carried out using, for example, a commercially available bipolar membrane electrodialysis apparatus. As an example, the bipolar membrane electrodialysis apparatus 1 shown in Figure 3 (hereinafter also simply referred to as "electrodialysis apparatus 1") has an anode 2 and a cathode 3 in a cell, and a bipolar membrane 4, an anion exchange membrane 5, a cation exchange membrane 6, and a bipolar membrane 7 arranged sequentially between the anodes 2 and 3 from the anode 2 side to the cathode 3 side. As a result, the cell is divided into a desalination 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 constructed by overlapping a cation exchange layer and an anion exchange layer.

[0067] To perform electrodialysis with the electrodialysis apparatus 1 shown in the figure, a metal-containing solution is placed in the desalination chamber R1, and pure water is placed in the acid chamber R2 and alkali chamber R3, respectively, 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 desalination chamber R1 are removed. + ) passes through the cation exchange membrane 6 and moves to the alkaline chamber R3. In the alkaline chamber R3, water (H2O) is decomposed by the bipolar membrane 7 and hydroxide ions (OH) are formed. - Since ) is present, a lithium hydroxide solution can be obtained.

[0068] Meanwhile, 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 acid chamber R2. In the acid chamber R2, these anions and hydrogen ions (H₂O) generated from water (H₂O) by the bipolar membrane 4 are exchanged. + This generates acidic solutions such as sulfuric acid solutions. As a result, the lithium hydroxide solution obtained in alkaline chamber R3 contains almost no inorganic acid anions. Note that the inorganic acid anions are sulfate ions (SO4) in the illustrated example. 2- However, depending on the type of acid used in the acid leaching process, nitrate ions (NO3) may be present. - ) or chloride ions (Cl - ) may be the case.

[0069] In desalination chamber R1, lithium salts are separated from the metal-containing solution as described above, leaving behind the desalination solution. The anion concentration of inorganic acids tends to be higher in acidic solutions than in lithium hydroxide solutions, and also higher in the desalination solution than in lithium hydroxide solutions.

[0070] In this electrodialysis process, most of the fluoride ions, which are impurities in the metal-containing solution, move from the desalination chamber R1 to the acid chamber R2 through the anion exchange membrane 5 and are incorporated into the acidic solution. Silicon impurities can also migrate to the acidic solution. As a result, a lithium hydroxide solution containing almost no fluoride ions or silicon is obtained in the alkaline chamber R3. Therefore, the fluoride ion concentration in the lithium hydroxide solution is lower than that in the acidic solution.

[0071] Furthermore, it was found that most of the phosphorus impurities in the metal-containing solution did not pass through either the cation exchange membrane 6 or the anion exchange membrane 5, but remained in the desalination chamber R1. Therefore, the lithium hydroxide solution obtained by electrodialysis contains almost no phosphorus. Consequently, the phosphorus concentration in the desalination solution remaining in the desalination chamber R1 after the lithium salt has been separated from the metal-containing solution is higher than the phosphorus concentration in 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 process. After electrodialysis, if necessary, the lithium ion concentration of the lithium hydroxide solution may be increased by heating or other means before it can be used as a pH adjuster.

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

[0074] In the crystallization process, crystallization operations such as heating and concentration or vacuum distillation can be performed to precipitate lithium hydroxide. In the case of heating and concentration, a higher temperature during crystallization is preferable because the process proceeds faster. However, after crystallization, the temperature at which the precipitate is dried should preferably be below 60°C to prevent the desorption of crystal water. This is because anhydrous lithium hydroxide from which crystal water has been desorbed is hygroscopic and difficult to handle.

[0075] As mentioned earlier, the lithium hydroxide solution obtained in the electrodialysis process is substantially free of inorganic acid anions such as sulfate ions. Therefore, the lithium hydroxide produced in the crystallization process is of high purity and superior quality.

[0076] Furthermore, the lithium hydroxide can subsequently be subjected to pulverization or other processes to adjust its physical properties to the required level. [Examples]

[0077] Next, we experimentally implemented the impurity removal method described above and confirmed its effectiveness, which is explained below. However, this explanation is for illustrative purposes only and is not intended to be an exhaustive limitation.

[0078] The metal-containing solution obtained by leaching battery powder with sulfuric acid was subjected to neutralization, manganese extraction, cobalt extraction, and nickel extraction to separate each metal.

[0079] Next, the separated metal-containing solution was subjected to electrodialysis using a bipolar membrane electrodialysis apparatus (manufactured by Astom Co., Ltd.) having the structure shown in Figure 3. In this procedure, the desalination chamber, alkali chamber, acid chamber, and electrode chamber were filled with the metal-containing solution, pure water, and electrode solution, respectively, with the compositions shown in Figure 4. The electrodialysis was performed under a constant voltage of 32V.

[0080] The results are also shown in Figure 4. Note that the reason why the sum of the distribution ratios of each ion in the desalted solution after electrodialysis, lithium hydroxide solution, acidic solution, and electrode solution in Figure 4 does not equal 100% is thought to be due to variability in the analytical values ​​(for example, the portion that could not be quantified due to the lower limit of quantification of the analysis is not included).

[0081] Figure 4 shows that the fluoride ion concentration, phosphorus concentration, and silicon concentration in the lithium hydroxide solution obtained after electrodialysis are all sufficiently low. This indicates that electrodialysis can produce a lithium hydroxide solution from which most impurities have been removed.

[0082] From the above, it was found that the aforementioned impurity removal method can effectively remove impurities such as fluoride ions. [Explanation of Symbols]

[0083] 1. Bipolar membrane electrodialysis machine 2 Anode 3 cathode 4, 7 Bipolar membrane 5 Anion exchange membrane 6. Cation exchange membrane R1 Desalination room R2 acid chamber R3 Alkaline Room

Claims

1. A method for removing impurities from a metal-containing solution obtained by leaching battery powder from lithium-ion battery waste with acid, A metal separation step for separating lithium ions and other metal ions from the metal-containing solution containing lithium ions and other metal ions, Following the metal separation step, an electrodialysis step is performed on the metal-containing solution containing lithium ions and impurity fluoride ions using a bipolar membrane to obtain a lithium hydroxide solution and an acidic solution. Includes, A method for removing impurities, wherein the lithium hydroxide solution is used as a pH adjusting agent in the metal separation step.

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, The impurity removal method according to claim 1, wherein the lithium hydroxide solution is used as a pH adjuster in the solvent extraction.

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

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

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

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

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 a dealuminization step. During the period before the aluminization step is completed, a phosphate ion source is added to the metal-containing solution to make phosphate ions present. The impurity removal method according to claim 1, wherein in the aluminum dealuminization step, aluminum ions in the metal-containing solution are reacted with phosphate ions to separate the aluminum ions from the metal-containing solution.

11. A method for recovering metal from battery powder of lithium-ion battery waste, comprising using the impurity removal method described in any one of claims 1 to 9.

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