Method for removing aluminum and method for recovering metal

Abstract

Provided are a method for removing aluminum and a method for recovering metal with which it is possible to effectively remove aluminum without excessively increasing the pH. This method for removing aluminum from a metal-containing solution that contains aluminum and that is obtained from battery powder of lithium-ion battery waste includes a pH increase step for increasing the pH of the metal-containing solution to obtain a precipitate containing aluminum. The metal-containing solution before the pH is increased in the pH increase step contains fluorine. The molar ratio (F / Al) of aluminum to fluorine in the metal-containing solution is 1.0 or less.

Description

Method for removing aluminum and method for recovering metal

[0001] This specification describes a method for removing aluminum and a method for recovering metal.

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

[0003] To recover valuable metals from lithium-ion battery waste, wet processing may be performed on battery powder obtained by subjecting lithium-ion battery waste to heat treatment or other predetermined dry pretreatment.

[0004] In wet processing, for example, metals such as cobalt, nickel, manganese, lithium, aluminum, and iron in battery powder are leached with an acid to obtain a metal-containing solution in which the metals are dissolved. Next, aluminum, iron, manganese, etc. are removed, and cobalt, nickel, etc. are separated from the metal-containing solution by adjusting pH or solvent extraction. Thereafter, a lithium-containing solution in which lithium is dissolved and remains is obtained.

[0005] Here, regarding removing aluminum and the like from a metal-containing solution by adjusting pH, Patent Document 1 describes "a method for recovering a high-purity cobalt compound from lithium-ion battery waste, characterized by comprising: (A) leaching a lithium-ion battery waste material containing a cobalt component with an inorganic acid; (B) adjusting the molar ratio of phosphorus to aluminum ions in the leached aqueous solution to 0.6 to 1.2, oxidizing iron ions at an oxidation potential of 500 mV or more; (C) adjusting the pH of the aqueous solution to 3.0 to 4.5, precipitating and removing impurity metals to obtain a purified solution; (D) adding oxalic acid to the purified solution to obtain cobalt oxalate, or adjusting the pH of the purified solution to 6 to 10 to precipitate and obtain cobalt hydroxide or cobalt carbonate".

[0006] Furthermore, Patent Documents 2 and 3 describe "a method for processing lithium-ion battery waste, comprising: a leaching step of leaching battery powder obtained from lithium-ion battery waste, which contains at least aluminum and iron, with acid, removing the leaching residue by solid-liquid separation to obtain a post-leaching solution containing at least aluminum ions and iron ions; and a neutralization step of adding phosphoric acid and / or phosphate and an oxidizing agent to the post-leaching solution, raising the pH to within the range of 2.0 to 3.5, precipitating the aluminum ions and iron ions in the post-leaching solution as aluminum phosphate and iron phosphate, respectively, and removing the neutralization residue by solid-liquid separation to obtain a neutralized solution."

[0007] Japanese Patent Publication No. 11-6020, Japanese Patent Publication No. 2022-94152, U.S. Patent Application Publication No. 2024 / 0047776

[0008] By the way, in order to sufficiently remove aluminum by adjusting the pH of a metal-containing solution, it is necessary to raise the pH to a certain level. On the other hand, if the pH is raised too high, not only the aluminum, which is the metal to be removed, but also other metals such as cobalt, which need to remain in the metal-containing solution, will precipitate, resulting in the loss of those other metals as well.

[0009] This specification provides an aluminum removal method and a metal recovery method that can effectively remove aluminum without raising the pH to a very high value.

[0010] One aluminum removal method disclosed in this specification is a method for removing aluminum from a metal-containing solution containing aluminum obtained from battery powder of lithium-ion battery waste, comprising a pH-raising step of raising the pH of the metal-containing solution to obtain an aluminum-containing precipitate, wherein the metal-containing solution before raising the pH in the pH-raising step contains fluorine, and the molar ratio of aluminum to fluorine in the metal-containing solution (F / Al) is 1.0 or less.

[0011] Furthermore, another aluminum removal method disclosed in this specification is a method for removing aluminum from a metal-containing solution containing aluminum obtained from battery powder of lithium-ion battery waste, comprising a pH-raising step of raising the pH of the metal-containing solution to obtain an aluminum-containing precipitate, wherein the aluminum concentration of the metal-containing solution before raising the pH in the pH-raising step is 0.5 g / L or more and 6.0 g / L or less, and the fluorine concentration is higher than 0 g / L and 3.0 g / L or less.

[0012] The metal recovery method disclosed in this specification is a method for recovering metal from battery powder of lithium-ion battery waste, comprising an acid leaching step of leaching the battery powder with acid to obtain a metal-containing solution in which metals including aluminum are dissolved, and a pH raising step of any of the aluminum removal methods described above.

[0013] According to the aluminum removal method described above, aluminum can be effectively removed without raising the pH to a very high value.

[0014] This is a flowchart showing an example of a metal recovery method including an aluminum removal method according to one embodiment. This is a flowchart showing an example of a pretreatment process for obtaining battery powder from lithium-ion battery waste.

[0015] The embodiments of the aluminum removal method and metal recovery method described above will be explained in detail below. One embodiment of the aluminum removal method includes a pH raising step in which an aluminum-containing precipitate is obtained by raising the pH of the metal-containing solution. The metal-containing solution is obtained from battery powder of lithium-ion battery waste and contains at least aluminum (Al 3+ This includes (etc.).

[0016] The metal-containing solution subjected to the pH-raising step contains fluorine before the pH is raised, and the molar ratio of aluminum to fluorine (F / Al) is 1.0 or less. In addition to or instead of this, the metal-containing solution before the pH is raised may have an aluminum concentration of 0.5 g / L or more and 6.0 g / L or less, and a fluorine concentration higher than 0 g / L and 3.0 g / L or less.

[0017] In this way, aluminum can be effectively removed without raising the pH of the metal-containing solution to a very high value during the pH-raising process. The reason for this is that by lowering the fluorine concentration relative to the aluminum concentration in the metal-containing solution, much of the aluminum will form complexes with fluorine (for example, (AlF6)). 3- This is thought to be because it does not form compounds (such as ions) and can exist in the solution in the form of cations, which makes it easier for aluminum hydroxide and other compounds to form and precipitate even at relatively low pH levels. However, this theory is not the only one that is considered to exist.

[0018] The aluminum removal method described above may be incorporated into a metal recovery method, as shown in Figure 1, for example. The metal recovery method in Figure 1 includes, in this order, an acid leaching step, a pH raising step, an extraction step (manganese extraction, cobalt extraction, nickel extraction, etc.), a hydroxide step, and a crystallization step. The metal-containing solution may be obtained by leaching battery powder from lithium-ion battery waste in the acid leaching step. Battery powder can be obtained by performing a pretreatment step on lithium-ion battery waste as shown in Figure 2. The metal recovery method according to Figures 1 and 2 will be described in detail below, but Figures 1 and 2 are illustrative and not limited to such specific flows.

[0019] (Lithium-ion battery waste) The lithium-ion battery waste covered by this analysis consists of lithium-ion secondary batteries that can be used in mobile phones and other various electronic devices, and which have been discarded due to the battery product's lifespan, manufacturing defects, or other reasons. Recovering valuable metals from such lithium-ion battery waste is desirable from the standpoint of effective resource utilization.

[0020] Lithium-ion battery waste may have an aluminum-containing casing, and within that casing may be a positive electrode active material consisting of lithium and a single metal oxide or a composite metal oxide containing two or more of these metals, or an aluminum foil (positive electrode substrate) on which the positive electrode active material is coated and fixed with, for example, polyvinylidene fluoride (PVDF) or other organic binders.

[0021] Furthermore, lithium-ion battery waste may contain copper, iron, etc., in components such as the negative electrode and casing. In addition, the casing may contain an electrolyte solution in which an electrolyte such as lithium hexafluoride phosphate is dissolved in an organic solvent such as ethylene carbonate or diethyl carbonate. Moreover, lithium-ion battery waste may contain separators coated with fluorine-based compounds.

[0022] (Pre-treatment process) In most cases, lithium-ion battery waste undergoes a pre-treatment process for dry processing. Lithium-ion battery waste becomes battery powder through the pre-treatment process. The pre-treatment process may include at least one of the following: heat treatment, crushing, and physical separation. The heat treatment, crushing, and physical separation in the pre-treatment process may be performed individually as needed, and may be performed in any order. Battery powder refers to powder obtained by separating and concentrating the positive electrode material components through some kind of pre-treatment of lithium-ion battery waste. Battery powder can also be obtained as a powder by concentrating the positive electrode material components by crushing and physical separation of lithium-ion battery waste, with or without heat treatment.

[0023] In the heat treatment, the lithium-ion battery waste described above is heated. Heat treatment decomposes and removes the electrolyte and organic binder, and metals such as lithium and cobalt contained in the lithium-ion battery waste can be transformed into a form that is easily soluble in the acidic leaching solution during the acid leaching process. Although the composition of the positive electrode active material changes due to heat treatment, it is still referred to as positive electrode active material in this context. During heat treatment, the lithium-ion battery waste is heated and maintained at a temperature range of, for example, 100°C to 800°C for 0.5 to 6 hours. The heat treatment can be performed in an atmospheric environment or an inert atmosphere such as nitrogen, and the heat treatment may be carried out in either this order or the reverse order. As the heat treatment furnace, for example, a batch-type stationary furnace or a continuous-type rotary kiln furnace or various other types of furnaces can be used.

[0024] From the viewpoint of preventing fluorine in the battery powder obtained after the pretreatment process from being leached out by the acid in the acid leaching process described later, it is desirable to keep the heating temperature of the lithium-ion battery waste in the heat treatment below the decomposition temperature of the fluorine-containing resin, specifically, for example, below 400°C, and even below 350°C. Also, from a similar viewpoint, the heat treatment in the pretreatment process may be omitted. This suppresses the leaching of fluorine in the acid leaching process, reduces the F / Al ratio of the metal-containing solution before the pH increase in the pH increase process, and / or reduces the amount of fluorine.

[0025] In crushing, the casing of the lithium-ion battery waste is destroyed, and the positive electrode active material is selectively separated from the aluminum foil coated with the positive electrode active material. Various known devices or equipment can be used for crushing, but it is particularly preferable to use an impact-type crusher that can crush the 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.

[0026] After crushing lithium-ion battery waste, physical separation can be performed, such as sieving using a sieve with an appropriate mesh size. This results in battery powder where aluminum and copper remain on the sieve and aluminum and copper have been removed to some extent below the sieve. Other physical separation methods may be performed in conjunction with or instead of sieving. By appropriately setting the conditions of the physical separation screen, the aluminum content in the battery powder can be adjusted.

[0027] To reduce the F / Al ratio of the metal-containing solution described later, or to reduce fluorine content, separators may be separated and removed from lithium-ion battery waste at any time, such as before the heat treatment or crushing described above, or the electrolyte may be washed away and removed. Lithium-ion battery waste may also be dismantled manually. Furthermore, to achieve a reduction in the F / Al ratio and fluorine content of the metal-containing solution, the selection of lithium-ion battery waste and the determination of its processing volume can be appropriately carried out. The fluorine and aluminum content may vary depending on the type of lithium-ion battery. A mixture of two or more battery powders with different fluorine content relative to aluminum (e.g., battery powder with relatively high fluorine content and battery powder with relatively low fluorine content) may be used as the battery powder for the acid leaching process.

[0028] Furthermore, in order to extract essentially only lithium from the battery powder, the battery powder may be brought into contact with water before the acid leaching process described later, allowing the lithium in the battery powder to leach into the water. In this case, the acid leaching process is performed on the battery powder remaining as a residue after the water leaching. However, the battery powder may also 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] The battery powder obtained in the pretreatment step, if it contains nickel, has a nickel content of, for example, 1% to 30% by mass, typically 5% to 20% by mass. If it contains cobalt, the cobalt content in the battery powder is, for example, 1% to 30% by mass, typically 5% to 20% by mass. The battery powder may also contain, for example, 2% to 8% by mass of lithium, 1% to 30% by mass of manganese, 1% to 10% by mass of aluminum, 1% to 5% by mass of iron, 1% to 10% by mass of copper, and 1% to 10% by mass of fluorine. The content of elements other than fluorine in the battery powder is determined by dissolving the battery powder in acid and quantifying the dissolved components using an ICP emission spectrometer. The fluorine content is measured by heating the battery powder and measuring it by ion chromatography. Such battery powder is subjected to a wet treatment including the acid leaching step described below.

[0030] (Acid leaching process) In the acid leaching process, the battery powder is brought into contact with an acidic leaching solution containing mineral or inorganic acids such as sulfuric acid, hydrochloric acid, or nitric acid to leach the battery powder. This dissolves mainly the metals in the battery powder, and a post-leaching solution containing these metals as metal ions is obtained. Here, a solution containing the metals in the battery powder as metal ions is referred to as a metal-containing solution. The metal-containing solution includes the post-leaching solution obtained in the acid leaching process and sent to the subsequent metal separation process, as well as solutions obtained during or between the pH increase process and the extraction process.

[0031] Regarding pH, the acidic leachate during leaching is preferably -0.5 to 3.0, while the post-leaching solution after leaching is complete may have a pH of 0.5 to 2.0. During leaching, for example, the acidic leachate may be stirred at 100 rpm to 400 rpm using a stirrer as needed, and the liquid temperature may be set to 50°C to 80°C, and further to 65°C to 70°C.

[0032] The metal-containing solution (post-leaching solution) obtained in the acid leaching process may have concentrations such as: cobalt (10 g / L to 50 g / L), nickel (10 g / L to 50 g / L), manganese (0 g / L to 50 g / L), lithium (3 g / L to 15 g / L), aluminum (1.0 g / L to 20 g / L), iron (0.1 g / L to 5.0 g / L), copper (0.005 g / L to 0.2 g / L), and fluorine (0.1 g / L to 5 g / L). The metal concentration in the solution can be confirmed by analysis using an ICP emission spectrometer. The fluorine concentration can be measured by ion chromatography.

[0033] (pH raising step) In the pH raising step, the pH of the metal-containing solution obtained in the acid leaching step is increased, thereby precipitating aluminum and other materials to obtain an aluminum-containing precipitate.

[0034] Here, it is crucial that, before increasing the pH, the metal-containing solution contains fluorine, and that the F / Al ratio of the metal-containing solution is 1.0 or less (Condition 1), and / or that the metal-containing solution contains aluminum at a concentration of 0.5 g / L or more and 6.0 g / L or less, and fluorine at a concentration of 3.0 g / L or less (Condition 2).

[0035] Furthermore, if the metal-containing solution used in the pH-raising process already satisfies conditions 1 and / or 2 above, no special operation is required before raising the pH.

[0036] From the viewpoint of effectively removing aluminum at a low pH when the pH is increased, the lower the F / Al ratio of the metal-containing solution, the more desirable, and preferably it is 0.6 or less. The F / Al ratio before pH increase may be, for example, 0.05 or higher, and even 0.1 or higher. The metal-containing solution contains fluorine, which originates from the electrolyte of lithium-ion battery waste, etc.

[0037] Before the pH is raised, the aluminum concentration in the metal-containing solution is preferably 1 g / L to 15 g / L, and the fluorine concentration is preferably 0.1 g / L to 5 g / L. A certain amount of aluminum reduces the F / Al ratio, making it easier to remove at low pH, while keeping the amount low suppresses residue in the solution after the pH-raising process. Fluorine and aluminum can exist in the metal-containing solution in the form of ions or complexes. Here, the concentrations of fluorine and aluminum refer to the amount contained in the metal-containing solution, regardless of their form.

[0038] In the process of removing aluminum by raising the pH (also called the "dealuminization process"), the pH of the metal-containing solution can be increased by adding an alkaline pH adjusting agent to the metal-containing solution. In the dealuminization process, as described above, by adjusting the F / Al and / or aluminum and fluorine concentrations, the pH can be raised to a relatively small value, for example, within the range of 2.5 to 4.0, 3.0 to 4.0, preferably 2.8 to 3.0, allowing aluminum to precipitate and be effectively removed. Therefore, the precipitation of cobalt and nickel that occurs when the pH is raised to a large value to remove aluminum is suppressed, and the loss of these valuable metals can be reduced.

[0039] In the dealuminumization process, an alkaline pH adjuster is added. When the pH increases to a certain level, for example 2.5 to 4.0, preferably 3.0 to 3.5, it is preferable to add iron instead of the alkaline pH adjuster to further increase the pH. This allows the pH to rise gently and increases the precipitation amount of aluminum. In addition, when iron ions are present in the metal-containing solution, if the pH is increased to a certain level by adding a pH adjuster, nickel ions in the metal-containing solution will precipitate as composite oxides with nickel oxide and iron, resulting in nickel loss. Switching from a pH adjuster to iron can also suppress this phenomenon. When iron is added, Fe + 2H + →Fe 2+ + H2 the amount of H in the solution decreases according to the reaction formula, and the pH rises. + In addition, the redox potential decreases. At this time, compared with the case where the pH is increased without switching from an alkaline pH adjuster to iron, the precipitation of nickel is suppressed, so nickel loss can be effectively prevented.

[0040] When switching the pH adjuster to iron during the dealuminumization process, iron-containing substances in various shapes such as powder, flake and block can be added to the metal-containing solution after the switching. Among them, powdered iron-containing substances (especially iron powder) are preferred. The iron-containing substance does not necessarily need to be 100% pure, and may be a commercially available product containing impurities such as oxygen, carbon, magnesium, aluminum, silicon, phosphorus, sulfur, chromium, manganese, nickel, and copper. However, if the proportion of impurities is too high, it may affect the subsequent extraction process, so a high-purity product is preferred.

[0041] In the dealuminization process, it is preferable to raise the pH of the metal-containing solution in the presence of phosphoric acid. This makes it easier for aluminum in the metal-containing solution to precipitate with phosphoric acid, allowing for more effective removal of aluminum. At this time, the iron ions in the metal-containing solution subjected to the dealuminization process should include divalent iron ions. This suppresses the consumption of phosphoric acid due to reaction with trivalent iron ions, allowing aluminum to precipitate with a smaller amount of phosphoric acid. When the metal-containing solution contains phosphoric acid, the precipitate generated in the dealuminization process may include compounds such as aluminum orthophosphate (AlPO4).

[0042] In a metal-containing solution, aluminum and phosphoric acid are reacted according to the formula: Al 3+ +PO4 3- →While the reaction is thought to occur with AlPO4, etc., when starting the dealuminization process, it is preferable to set the amount of phosphoric acid in the metal-containing solution to 0.1 to 1.5 times the molar equivalent of the amount required for the reaction with aluminum in the metal-containing solution.

[0043] Since the dealuminization process is carried out in the presence of phosphoric acid in the metal-containing solution, a phosphoric acid source may be added to the acidic leaching solution in the acid leaching step or to the metal-containing solution before the dealuminization process in the pH raising step. As a phosphoric acid source, the metal-containing solution may be converted into phosphate ions (PO4) upon contact with the acidic leaching solution. 3- If the material contains phosphoric acid, such as phosphate, then various types can be used. Specifically, examples include phosphoric acid (H3PO4), calcium phosphate (Ca3(PO4)2, etc.), calcium hydrogen phosphate (CaHPO4), trisodium phosphate (Na3PO4), disodium hydrogen phosphate (Na2HPO4), sodium dihydrogen phosphate (NaH2PO4), and lithium phosphate (Li3PO4). However, if the battery powder contains phosphorus (P), then the addition of a phosphoric acid source may not be necessary.

[0044] When the dealuminumization process is completed, the phosphorus concentration of the metal-containing solution is preferably in the range of 0.4 g / L to 1.0 g / L. After phosphoric acid is sufficiently consumed in the dealuminumization process to lower the phosphorus concentration in this manner, the process described below may be performed subsequently.

[0045] After the completion of the dealuminumization process, if the metal-containing solution contains iron ions, a process for further removing iron (also referred to as a "deironization process") may be performed. In the deironization process, an oxidizing agent is added to the metal-containing solution after the dealuminumization process to oxidize the iron ions, and the pH is further increased as needed, thereby precipitating and removing the iron ions.

[0046] The oxidizing agent used in the deironization process is not particularly limited as long as it can oxidize iron, but it is preferably hydrogen peroxide, manganese dioxide, a positive electrode active material, and / or a manganese-containing leaching residue obtained by leaching a positive electrode active material. The oxidation-reduction potential during oxidation (ORP vs Ag / AgCl) may be 300 mV to 900 mV. In the deironization process, the pH of the metal-containing solution may also be increased to a value within the range of 3.0 to 5.0. If the metal-containing solution contains substantially no iron ions, the deironization process may be omitted.

[0047] In the pH increasing step (such as the dealuminumization process, the deironization process, etc.), for example, lithium hydroxide, sodium hydroxide, sodium carbonate, ammonia or the like can be used as an alkaline pH adjuster. Among these, for lithium hydroxide, from the viewpoint of cost reduction, it is preferable to use lithium hydroxide generated from lithium extracted by wet processing (such as a lithium hydroxide solution obtained after the hydroxylation step described later).

[0048] After precipitation of aluminum in the dealuminumization process and after precipitation of iron in the deironization process, solid-liquid separation such as filtration is performed using a known apparatus and method such as a filter press or a thickener, thereby removing the precipitate obtained in each process.

[0049] (Extraction Process) As an example, in the extraction process, manganese extraction, cobalt extraction, and nickel extraction may be performed in this order.

[0050] In manganese extraction, after the pH-raising step, the metal-containing solution can be extracted and removed by solvent extraction to remove manganese ions, and possibly residual aluminum ions as well. In this case, the manganese ion and residual aluminum ions are extracted, resulting in a post-manganese extract solution from which they have been removed.

[0051] For the extraction of manganese ions, a phosphate ester extractant (such as di-2-ethylhexyl phosphate (abbreviation: D2EHPA or trade name: DP-8R)) or a mixture of a phosphate ester extractant and an aldoxime or aldoxime-based oxime extractant (such as 2-hydroxy-5-nonylacetophenone oxime (trade name: LIX84), 5-dodecylsalicylaldoxime (trade name: LIX860), a mixture of LIX84 and LIX860 (trade name: LIX984), 5-nonylsalicylaldoxime (trade name: ACORGAM5640)) can be used. The extractant may be diluted with a hydrocarbon organic solvent such as aromatic, paraffinic, or naphthenic solvent to a concentration of 10% to 30% by volume, and this may be used as the solvent.

[0052] During the extraction of manganese ions, the equilibrium pH is preferably set to 2.3 to 3.5, more preferably to 2.5 to 3.0. From the viewpoint of cost reduction, it is preferable to use lithium hydroxide produced from lithium extracted by wet treatment (such as the lithium hydroxide solution obtained after the hydroxide step described later) as the alkaline pH adjusting agent at this time, but lithium hydroxide or the like prepared separately may also be used.

[0053] When extracting manganese ions, it is desirable to perform the extraction using 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 other metal ions such as cobalt ions, nickel ions, and lithium ions, and increases 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 range mentioned above, and then increase the equilibrium pH during extraction with each subsequent stage. Counter-flow multi-stage extraction is also preferable for cobalt extraction and nickel extraction, which will be discussed later.

[0054] In cobalt extraction, cobalt ions are separated from the metal-containing solution obtained as a post-extract after manganese extraction by solvent extraction. During this process, magnesium ions that may be present in the metal-containing solution are also extracted and removed. Here, it is preferable to use a solvent containing a phosphonic acid ester extractant such as 2-ethylhexyl 2-ethylhexylphosphonate (trade names: PC-88A, Ionquest 801).

[0055] During cobalt ion extraction, the equilibrium pH can be preferably set to 5.0 to 6.0, more preferably to 5.0 to 5.5. In this case, from the viewpoint of cost reduction, lithium hydroxide produced from lithium extracted by wet processing (such as the lithium hydroxide solution obtained after the hydroxide step described later) may be used as the pH adjusting agent. However, if the pH adjusting agent used here contains impurities, it may lead to a decrease in the quality of the final cobalt salt. Therefore, depending on the purity of the lithium hydroxide solution, it may be preferable to use commercially available lithium hydroxide or other relatively high-purity product prepared separately as the pH adjusting agent.

[0056] After scrubbing the solvent from which cobalt ions have been extracted, back-extraction can be performed using a back-extract solution containing sulfuric acid, hydrochloric acid, or nitric acid, for example, at a pH of 2.0 to 4.0. Subsequently, the back-extracted solution can be heated and concentrated to crystallize the cobalt ions as cobalt salts such as cobalt sulfate.

[0057] In nickel extraction, nickel ions are separated from the metal-containing solution obtained as a post-extraction liquid after the extraction of cobalt ions by solvent extraction. Suitable solvents include those containing carboxylic acid-based extractants such as neodecanoic acid and naphthenic acid.

[0058] At this time, the equilibrium pH is preferably set to 6.0 to 8.0, more preferably to 6.8 to 7.2. From the viewpoint of cost reduction, the pH adjusting agent used to adjust this equilibrium pH may be lithium hydroxide produced from lithium extracted by wet processing (such as the lithium hydroxide solution obtained after the hydroxide step described later), but in order to suppress the decrease in the purity of nickel salts, it is preferable to use commercially available lithium hydroxide or the like that which has been prepared separately and is of relatively high purity.

[0059] After scrubbing the solvent from which nickel ions have been extracted, back-extraction can be performed using a back-extract solution containing sulfuric acid, hydrochloric acid, or nitric acid, for example, at a pH of 1.0 to 3.0. Subsequently, the back-extracted solution can be electrolyzed and dissolved as needed, then heated and concentrated to crystallize the nickel ions as nickel salts such as nickel sulfate.

[0060] At least a portion of the lithium-containing solution after nickel ions have been extracted may be mixed with the acidic leachate in the acid leaching step and used. This allows the lithium ions contained in the lithium-containing solution to be circulated throughout the series of steps from the acid leaching step to the nickel extraction step. Preferably, after the lithium ion concentration in the lithium-containing solution has increased to a certain extent by circulating the lithium ions in this way, the organic matter removal step described below can be carried out.

[0061] (Hydroxide process) The lithium-containing solution obtained after the extraction process (nickel extraction in the above example) contains substantially only lithium ions, as a result of the separation of manganese ions, cobalt ions, and nickel ions in each of the extractions described above. In the hydroxide process, a lithium hydroxide solution is prepared from the above lithium-containing solution (lithium sulfate solution, etc.) by various methods described below.

[0062] For example, a lithium carbonate solution can be obtained by first adding a carbonate to a lithium sulfate solution or by blowing in carbon dioxide. Then, using a so-called chemical conversion method, calcium hydroxide can be added to the lithium carbonate solution, and a lithium hydroxide solution can be produced according to the reaction equation Li₂CO₃ + Ca(OH)₂ → 2LiOH + CaCO₃. Calcium ions that may remain in the solution can be removed using cation exchange resins or chelating resins.

[0063] Alternatively, a lithium hydroxide solution can be obtained by adding barium hydroxide to a lithium sulfate solution and following the reaction Li₂SO₄ + Ba(OH)₂ → 2LiOH + BaSO₄. The barium that may dissolve in the solution at this time can be separated and removed using a cation exchange resin or chelating resin.

[0064] Alternatively, when employing the so-called electrolytic method, a lithium hydroxide solution can be generated on the cathode side by supplying a lithium sulfate solution to the anode side and performing electrolysis in an electrolytic cell equipped with a cation exchange membrane that separates the anode side and the cathode side.

[0065] In this electrolytic method, a lithium sulfate solution is sometimes supplied to the desalination chamber between the anion exchange membrane and the cation exchange membrane in a bipolar membrane electrodialysis machine, and electrodialysis is performed. In this case, a lithium hydroxide solution may be obtained in the alkaline chamber between the cation exchange membrane and the bipolar membrane, while an acidic solution such as sulfuric acid may be obtained in the acidic chamber between the bipolar membrane and the anion exchange membrane.

[0066] Furthermore, lithium-containing solutions may contain trace amounts of cations such as nickel and magnesium ions that were not completely separated during the extraction 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 lithium-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, it is desirable to wash the lithium-containing solution to remove cations such as nickel and magnesium ions prior to electrodialysis. For example, ion exchange resins or chelate resins can be used for this washing.

[0067] The lithium hydroxide solution obtained as described above can be effectively used not only as a pH adjuster (neutralizing agent) in neutralization, but also as an alkaline pH adjuster in manganese extraction, cobalt extraction, and nickel extraction.

[0068] (Crystallization process) The lithium hydroxide solution obtained in the hydroxide process can be subjected to the crystallization process. For example, as described above, if the lithium hydroxide solution is returned to the wet process 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 process. The crystallization process may be carried out according to the lithium ion concentration to recover the lithium hydroxide.

[0069] In the crystallization process, crystallization operations such as heating and concentration or vacuum distillation can be performed to precipitate lithium hydroxide. In the case of heating and concentration, a higher temperature during crystallization is preferable as it speeds up the process. However, after crystallization, the temperature at which the precipitate is dried should preferably be below 60°C to prevent the desorption of crystal water. This is because anhydrous lithium hydroxide from which crystal water has been desorbed is hygroscopic and difficult to handle. The lithium hydroxide produced in the crystallization process may be subjected to pulverization or other treatments to adjust its physical properties to the required level.

[0070] (Potential Contribution to SDGs) According to the embodiment described above, aluminum can be effectively removed without raising the pH to a very high value, which may reduce the loss of valuable metals such as cobalt and nickel. For this reason, this embodiment may contribute to Goal 9, "Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation," and Goal 12, "Ensure sustainable consumption and production patterns," of the United Nations-led Sustainable Development Goals (SDGs).

[0071] Next, we will describe the results of a trial implementation of the aluminum removal method described above, and the confirmation of its effectiveness. However, this explanation is for illustrative purposes only and is not intended to be an exhaustive list. In the following tests, an ICP emission spectrometer SPS3300 manufactured by SII Nanotechnology Co., Ltd. was used to measure the metal ion concentration, and a multi-water quality meter MX-43X and a composite electrode GST-5841C manufactured by Toa DKK Co., Ltd. were used to measure the pH.

[0072] A metal-containing solution was obtained by pre-treating lithium-ion battery waste and then leaching the resulting battery powder with sulfuric acid. As for the pre-treatment, in Example 1, the lithium-ion battery was manually disassembled and then physically separated; in Examples 2 and 4, the lithium-ion battery waste was crushed and then physically separated; and in Examples 3 and 5, the lithium-ion battery waste was crushed, then heat-treated at 300°C, and then physically separated. In the comparative example, as pre-treatment, heat treatment at 590°C under a nitrogen atmosphere and heat treatment at 400°C under an air atmosphere were performed sequentially, followed by crushing, and then physically separated.

[0073] In Examples 1-5, lithium hydroxide was added to the metal-containing solution as an alkaline pH adjuster, followed by the addition of iron powder to raise the pH and precipitate aluminum. In Examples 4 and 5, calcium phosphate was added to the metal-containing solution beforehand, and then lithium hydroxide and iron powder were added. In the comparative example, sodium hydroxide was used as the alkaline pH adjuster, and iron powder was not used.

[0074] The conditions or results for each stage are shown in Table 1. In Table 1, the Ni loss rate and Co loss rate were determined by dissolving the solid material in acid and calculating the quality using an ICP emission spectrometer.

[0075]

[0076] In all of Examples 1 to 5, the F / Al ratio of the metal-containing solution before pH increase was 1.0 or less, and the solution contained aluminum at a concentration of 0.5 g / L or more and 6.0 g / L or less, and fluorine at a concentration of 3.0 g / L or less. Therefore, the aluminum concentration in the metal-containing solution was sufficiently reduced without raising the pH to a very high level. As a result, the Ni loss rate and Co loss rate were reduced.

[0077] Furthermore, comparing Examples 2 and 4, and Examples 3 and 5, which had similar pretreatment conditions, it can be seen that aluminum was removed even more effectively at a lower pH in Examples 4 and 5. This is thought to be because the addition of calcium phosphate made it easier for aluminum in the metal-containing solution to precipitate with phosphoric acid. As a result, the Ni loss rate and Co loss rate were further reduced.

[0078] Comparing Examples 1 to 3, it can be seen that if the F / Al ratio is 0.6 or less, aluminum can be removed at a lower pH, and the Ni loss rate and Co loss rate can be further reduced.

[0079] In the comparative example, even with a significant increase in pH, aluminum removal was insufficient. This is thought to be because, due to the high F / Al ratio and high fluorine concentration, much of the aluminum formed complexes with fluorine, making precipitation difficult. Furthermore, as a result of significantly increasing the pH, the Ni loss rate and Co loss rate increased.

[0080] From the above, it was found that the aluminum removal method described above can effectively remove aluminum without raising the pH to a very high value.

Claims

1. A method for removing aluminum from a metal-containing solution obtained from battery powder of lithium-ion battery waste, comprising a pH-raising step of raising the pH of the metal-containing solution to obtain an aluminum-containing precipitate, wherein the metal-containing solution before raising the pH in the pH-raising step contains fluorine, and the molar ratio of aluminum to fluorine in the metal-containing solution (F / Al) is 1.0 or less.

2. The aluminum removal method according to claim 1, wherein, in the pH raising step, the F / Al ratio of the metal-containing solution before raising the pH is 0.6 or less.

3. The aluminum removal method according to claim 1, wherein, in the pH raising step, the aluminum concentration of the metal-containing solution before raising the pH is 0.5 g / L or more and 6.0 g / L or less.

4. The aluminum removal method according to claim 1, wherein, in the pH raising step, the fluorine concentration of the metal-containing solution before raising the pH is 3.0 g / L or less.

5. A method for removing aluminum from a metal-containing solution containing aluminum obtained from battery powder of lithium-ion battery waste, comprising a pH-raising step of raising the pH of the metal-containing solution to obtain an aluminum-containing precipitate, wherein the aluminum concentration of the metal-containing solution before raising the pH in the pH-raising step is 0.5 g / L or more and 6.0 g / L or less, and the fluorine concentration is higher than 0 g / L and 3.0 g / L or less.

6. The aluminum removal method according to any one of claims 1 to 5, wherein the metal-containing solution before the pH is raised in the pH raising step contains phosphoric acid.

7. The aluminum removal method according to any one of claims 1 to 5, wherein, in the pH raising step, the pH of the metal-containing solution is raised to a value within the range of 3.0 to 4.0 in order to remove aluminum.

8. A method for recovering metal from battery powder of lithium-ion battery waste, comprising: an acid leaching step of leaching the battery powder with an acid to obtain a metal-containing solution in which metals including aluminum are dissolved; and a pH raising step of the aluminum removal method according to any one of claims 1 to 5.

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