Metal leaching method and metal recovery method

Abstract

Provided are a metal leaching method and a metal recovery method, whereby a target metal is effectively leached using a relatively small amount of a reducing agent or without using the reducing agent and thus cost reduction can be achieved. The present invention relates to a method for leaching at least a target metal, which is at least one among cobalt and nickel, from a battery powder containing the target metal in the form of a metal oxide, the method having a leaching process comprising: a first leaching step in which the battery powder is brought into contact with an acidic first leachate, whereby a portion of the target metal in the metal oxide contained in the battery powder is leached into the first leachate and at least a portion of manganese ions contained in the first leachate is precipitated as a manganese oxide, and then a first post-leaching solution, which contains a portion of the target metal as metal ions, and a first leaching residue, which contains the remaining solids of the target metal and the manganese oxide, are obtained; and a second leaching step in which the first leaching residue is brought into contact with an acidic second leachate, whereby the target metal in the first leaching residue is leached into a second leachate, and then a second post-leaching solution containing the target metal as metal ions is obtained. The leaching process is repeated multiple times. In the multiple leaching processes, the second post-leaching solution from the previous leaching process is used as at least a portion of the first leachate in the next leaching process, and at least the first post-leaching solution is a metal-containing solution from which the target metal has been leached.

Description

Metal leaching method and metal recovery method

[0001] This specification describes a method for metal leaching and a method for metal recovery.

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

[0003] Processes for recovering metals from lithium-ion battery waste may include, for example, roasting or other prescribed pretreatment of the lithium-ion battery waste, and wet treatment of the battery powder obtained after such pretreatment.

[0004] In wet processing, metals such as cobalt, nickel, manganese, lithium, aluminum, and iron in the battery powder are leached with acid to obtain a metal-containing solution in which these metals have dissolved. Subsequently, aluminum ions, iron ions, and manganese ions are removed sequentially or simultaneously from the metal-containing solution by neutralization or solvent extraction, and then cobalt ions and nickel ions in the metal-containing solution may be separated by solvent extraction.

[0005] Techniques for leaching metals from battery powder using acid in a wet process include, for example, those described in Patent Documents 1 to 5.

[0006] Patent No. 6121359 Patent No. 6352846 Patent No. 6334450 Patent No. 6298002 Patent No. 6397111

[0007] Incidentally, in order to leach cobalt and / or nickel from battery powder containing these metal oxides into an acidic leaching solution, it may be necessary to use hydrogen peroxide or other reducing agents to dissolve the metal oxides. However, reducing agents are relatively expensive, and using large quantities will increase the cost required for leaching the metals from the battery powder.

[0008] This specification provides a metal leaching method and a metal recovery method that can effectively leach a target metal using a relatively small amount of reducing agent or without using any reducing agent, thereby contributing to cost reduction.

[0009] The metal leaching method described in this specification is a method for leaching at least one target metal from battery powder containing at least one of cobalt and nickel as a metal oxide, comprising contacting the battery powder with an acidic first leaching solution, leaching a portion of the target metal from the metal oxide contained in the battery powder into the first leaching solution, and precipitating at least a portion of the manganese ions contained in the first leaching solution as manganese oxide, and then obtaining a post-leaching solution containing a portion of the target metal as metal ions, and the remaining solid portion of the target metal and the manganese oxide. The leaching process includes a first leaching step to obtain a first leaching residue, and a second leaching step to bring the first leaching residue into contact with an acidic second leaching solution, thereby leaching the target metal in the first leaching residue into the second leaching solution, and obtaining a second post-leaching solution containing the target metal as metal ions. The leaching process is repeated multiple times, and in each of the multiple leaching processes, the second post-leaching solution from the previous leaching process is used as at least a portion of the first leaching solution in the next leaching process, so that the first post-leaching solution is a metal-containing solution in which at least the target metal has been leached.

[0010] The metal recovery method described in this specification involves recovering the metal from the metal-containing solution obtained by the metal leaching method described above.

[0011] According to the metal leaching method described above, the target metal can be effectively leached using a relatively small amount of reducing agent or without using any reducing agent, thereby contributing to cost reduction.

[0012] This is a flowchart showing the leaching process of a metal leaching method according to one embodiment. This is a flowchart showing an example of a metal recovery method including the metal leaching method of Figure 1. This is a graph showing an example of the stable region of chemical species in a liquid under specific conditions in a potential-pH diagram. This is a graph showing the relationship between the amount of hydrogen peroxide added and the leaching rate of each metal in Test Example 1. This is a graph showing the change in the leaching rate of each element as the leaching time progresses in Test No. 10 of Test Example 1. This is a graph showing the change in the leaching rate of each element as the leaching time progresses in Test No. 11 of Test Example 1. This is a graph showing the change in the leaching rate of each element as the leaching time progresses in Test No. 12 of Test Example 1. This is a flowchart showing the leaching process of Test Example 2. This is a graph showing the change in Mn concentration relative to ORP in the first leaching stage of Test Example 2. This is a graph showing the change in Mn concentration relative to ORP in the second leaching stage of Test Example 2.

[0013] The embodiments of the metal leaching method and metal recovery method described above will be explained in detail below. One embodiment of the metal leaching method is a method of leaching at least one of the target metals (also called the "target metal") from battery powder containing the target metal as a metal oxide, which is cobalt and nickel.

[0014] Metals in metal oxides are less likely to leach into acidic leaching solutions compared to elemental metals. Therefore, especially in the case of battery powder containing the target metal as a metal oxide, attempting to reduce the metal oxide with a reducing agent to leach the target metal into the leaching solution requires the use of a large amount of reducing agent, which leads to increased costs.

[0015] In contrast, this embodiment repeats the leaching process multiple times, changing the battery powder to be leached each time, and each leaching process includes a first leaching step and a second leaching step as illustrated in Figure 1. That is, after performing a leaching process including the first and second leaching steps on a given battery powder, the next leaching process including the first and second leaching steps is performed on a new battery powder. In the first leaching step, the battery powder is brought into contact with an acidic first leaching solution, causing a portion of the target metal in the metal oxide contained in the battery powder to leach into the first leaching solution, and at least a portion of the manganese ions contained in the first leaching solution to precipitate as manganese oxide, after which solid-liquid separation can be performed as needed. As a result, the metal oxide is reduced by the reaction in which manganese ions precipitate onto manganese oxide (also called the "manganese deposition reaction"), and the leaching of the target metal in the metal oxide is promoted. Therefore, the amount of reducing agent used can be reduced or decreased.

[0016] However, in this case, not all of the target metal is leached in the first leaching step; only a portion is leached, and the remainder remains as a solid. Therefore, the first leaching step yields a first leaching solution containing some of the target metal as metal ions, and a first leaching residue containing the remaining solid portion of the target metal and manganese oxide. A second leaching step is performed to leach the target metal contained in the first leaching residue. In the second leaching step, the first leaching residue is brought into contact with an acidic second leaching solution, allowing as much of the target metal in the first leaching residue as possible to leach into the second leaching solution, after which solid-liquid separation can be performed as needed. This allows the target metal that remained undissolved in the first leaching step and was contained in the first leaching residue to be leached in the second leaching step.

[0017] During the repeated leaching process, the second leaching solution from a predetermined leaching process (the previous leaching process) is used as at least a portion of the first leaching solution for the next leaching process applied to the new battery powder, and at least the first leaching solution is a metal-containing solution from which the target metal has been leached. The second leaching solution may also be a metal-containing solution if it contains almost no manganese ions. In the metal recovery method, a process is carried out to recover the metal from the above-mentioned metal-containing solution.

[0018] In short, the first leaching step utilizes the manganese deposition reaction to leach the target metal, and the subsequent second leaching step aims to leach any remaining target metal that did not dissolve in the first step. As a result, the overall amount of reducing agent used can be reduced or eliminated, and even target metals contained in metal oxides in battery powder can be effectively leached.

[0019] Furthermore, if one were to attempt to leach almost all of the target metal from the metal oxide in the battery powder in a single leaching process, it would be necessary to use a considerable amount of reducing agents and acids. This would cause the oxidation-reduction potential (ORP) and pH to fall outside the specified range. As a result, even if manganese ions are present in the leaching solution, the manganese deposition reaction would be less likely to occur, making it impossible to effectively utilize the solution.

[0020] The metal leaching method of this embodiment can be used in a process to recover metals from battery waste such as lithium-ion battery waste. Below, the metal leaching method will be described as an example of its application to the metal leaching in a metal recovery method for lithium-ion battery waste as illustrated in Figure 2. However, the metal leaching method is not limited to this and can be used in various methods that include a step of leaching metals in the battery powder of lithium-ion battery waste into an acidic leaching solution. In addition, it is possible to use battery powder obtained from battery waste other than lithium-ion battery waste, but here we will explain in detail the case in which battery powder is obtained from lithium-ion battery waste as an example. Battery waste refers to batteries that are subject to recycling, regardless of whether the battery waste is traded for a price, or traded free of charge or as industrial waste.

[0021] (Lithium-ion battery waste) Lithium-ion battery waste refers to lithium-ion secondary batteries used in vehicles or consumer products that have been discarded due to the end of their lifespan, manufacturing defects, or other reasons. Examples of lithium-ion secondary batteries used in vehicles include those contained in battery packs installed in vehicles such as hybrid cars and electric vehicles. Examples of lithium-ion secondary batteries used in consumer products include those used in mobile phones and various other electronic devices. Recovering cobalt, nickel, and other metals from such lithium-ion battery waste is required from the perspective of effective resource utilization. In addition, manganese and lithium may also be included in the recovery targets.

[0022] Lithium-ion battery waste includes positive electrode material, negative electrode material, electrolyte, and the surrounding aluminum casing, etc. Here, the positive electrode material and negative electrode material may be constructed by fixing the positive electrode active material or negative electrode active material onto a positive electrode current collector such as aluminum foil or a negative electrode current collector such as copper foil with, for example, polyvinylidene fluoride (PVDF) or other organic binder.

[0023] Of these, the positive electrode active material is, for example, a single metal oxide from among lithium, nickel, cobalt, and manganese, or a composite metal oxide of two or more of these. Examples of such positive electrode active materials include LiCoO2, LiNiO2, Li-Co-Ni-O, and Li-Co-Ni-Mn-O. The positive electrode active material contains valuable metals, and recovering such metals is desirable from the standpoint of effective resource utilization. Metals such as cobalt, nickel, and lithium contained in the positive electrode active material are subject to recovery here, regardless of their form, even if their form changes due to heat treatment or other processes described later.

[0024] Furthermore, carbon-based materials are sometimes used as the negative electrode active material, and the electrolyte is often 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.

[0025] In this embodiment, the subject may be lithium-ion battery waste that maintains the form of a lithium-ion battery product, or it may be process scrap. Process scrap is discarded from the lithium-ion battery manufacturing process before the electrolyte is injected to form a lithium-ion battery, and does not contain electrolyte. Typically, process scrap does not contain not only electrolyte, but also aluminum casings and copper-containing terminals. Specific examples of process scrap include positive electrode materials, where positive electrode active material is attached to a positive electrode current collector such as aluminum foil with an organic binder, laminates in which positive electrode material, negative electrode material, and separator are stacked, and wound bodies in which positive electrode material, negative electrode material, and separator are wound. In the manufacturing of lithium-ion batteries, after terminals are attached to the laminate or wound body and it is sealed in an casing, the electrolyte is injected. Materials discarded from the process before the electrolyte is injected and that do not contain electrolyte are considered process scrap. Such process scrap is also referred to as lithium-ion battery waste in this context.

[0026] (Pretreatment) Pretreatment often involves heat treatment, crushing, and sieving of lithium-ion battery waste in this order or in any order, although at least one of these treatments may be omitted. Battery powder is obtained by pretreatment of lithium-ion battery waste. Here, battery powder refers to the powder obtained by separating and concentrating the positive electrode material components after some kind of pretreatment of lithium-ion battery waste.

[0027] Battery powder can be obtained by heat-treating lithium-ion battery waste, followed by crushing and sieving to concentrate the positive electrode material components into a powder. Alternatively, battery powder can be obtained by crushing lithium-ion battery waste, followed by heat treatment to remove the electrolyte, and then sieving. Furthermore, battery powder can be obtained by crushing and sieving without heat treatment. For example, if the lithium-ion battery waste does not contain electrolyte, as in the process scrap described above, heat treatment may be omitted. The following explanation will use the case where heat treatment, crushing, and sieving are performed in this order on lithium-ion battery waste as an example.

[0028] The heat treatment is primarily performed to remove the electrolyte from lithium-ion battery waste. The temperature at which the lithium-ion battery waste is heated during the heat treatment is not particularly important. During the heat treatment, the lithium-ion battery waste may be heated to a temperature at which the electrolyte can be removed, for example, 100°C or higher, typically 100°C to 185°C or 185°C to 350°C. Alternatively, the lithium-ion battery waste may be heated at a relatively high temperature of 300°C or higher, for example 350°C to 650°C, particularly 400°C to 600°C, for 1 to 8 hours, either after heating at a low temperature or without heating at a low temperature. High-temperature heating can cause decomposition of LiCoO2 and other materials in the positive electrode active material, potentially generating cobalt oxide, metallic cobalt, lithium carbonate, etc.

[0029] Heating in heat treatment can be carried out under various atmospheres, such as an air atmosphere, an inert atmosphere, or a reduced-pressure atmosphere such as a vacuum. The atmosphere may be switched midway through the process, and heating under an air atmosphere and heating under an inert atmosphere may be performed in any order. The heat treatment furnace is not particularly limited, but for example, if it is a batch type, an atmosphere-type and vacuum-type electric furnace or an atmosphere-type muffle furnace can be used, or if it is a continuous type, a roller hearth kiln or a mesh belt kiln can be used.

[0030] After heat treatment, lithium-ion battery waste can be crushed. This crushing process destroys the casing of the lithium-ion battery waste and separates metals derived from the positive electrode, such as nickel and cobalt, from the aluminum foil. Various known crushers can be used for the crushing process, but specific examples include impact-type crushers that can crush the casing by applying impact while cutting it, such as sample mills, hammer mills, pin mills, wing mills, tornado mills, and hammer crushers.

[0031] After crushing, the crushed lithium-ion battery waste is further crushed or pulverized into a powder as needed, and then sieved using a sieve with an appropriate mesh size. This process leaves, for example, aluminum and copper on the sieve, while removing a certain amount of aluminum and copper to obtain battery powder containing lithium, cobalt, nickel, etc., below the sieve.

[0032] Furthermore, if necessary, the battery powder can be brought into contact with a liquid such as water before the metal leaching method described below to selectively leach lithium. In this case, tap water, industrial water, distilled water, purified water, ion-exchanged water, pure water, ultrapure water, etc., can be used, and the liquid temperature at the time of contact between the battery powder and the liquid can be 10°C to 60°C. The lithium solution obtained by lithium leaching can be subjected to treatments such as solvent extraction, neutralization, and carbonation to recover lithium in the lithium solution as lithium carbonate. The lithium carbonate obtained in this way may be purified as necessary to reduce the impurity content. When lithium leaching is performed in this manner, the residue after leaching is used as battery powder, and the metal leaching method described below is then carried out on it.

[0033] (Method for metal leaching) The battery powder obtained in the pretreatment contains the target metal as a metal oxide. In the metal leaching method, the target metal is leached out from the metal oxide contained in such battery powder.

[0034] The target metal contained in the battery powder is at least one of cobalt and nickel, and refers to cobalt alone, nickel alone, or both cobalt and nickel. The battery powder only needs to contain a metal oxide containing one of the above target metals and / or a composite oxide containing two of the target metals. The battery powder only needs to have at least a part of cobalt and / or nickel in the form of a metal oxide, and may further contain cobalt and / or nickel in other forms such as elemental metal other than metal oxide.

[0035] The battery powder may further contain manganese in the form of a metal oxide or the like. Typically, the battery powder contains cobalt and / or nickel and manganese as a composite metal oxide, and in addition or alternatively, cobalt and / or nickel and manganese may be contained as a single metal oxide. Examples of the metal oxide in the battery powder include CoO₂, NiO₂, MnO₂, Co₂O₃, Ni₂O₃, Mn₂O₃, Co₃O₄, Ni₃O₄, Mn₃O₄, CoO, NiO, MnO, Co-Ni-Mn-O, and the like. Although details will be described later in this embodiment, the post-second leaching solution containing manganese ions obtained in the second leaching step of a predetermined leaching process is used as at least a part of the first leaching solution in the first leaching step of the next leaching process. Therefore, even if the battery powder supplied to the first leaching step does not contain a large amount of manganese (for example, when the amount of manganese in the battery powder is less than the total amount of nickel and cobalt), nickel and cobalt in the battery powder can be effectively leached by the manganese precipitation reaction of the manganese ions described above. Therefore, the amount of hydrogen peroxide used can be lowered or reduced.

[0036] In the metal leaching method, the leaching process is repeated multiple times while changing the battery powder to be leached for each time. Each leaching process includes a first leaching step and a second leaching step as exemplified in FIG. 1.

[0037] In the first leaching step, as shown in FIG. 1, battery powder is brought into contact with an acidic first leachate containing sulfuric acid, hydrochloric acid, nitric acid or other acids. At this time, the first leachate is supposed to contain manganese ions. Manganese ions may be caused to exist in the first leachate by adding a manganese-containing substance such as manganese oxide including manganese dioxide (MnO₂) or the like to the first leachate and dissolving the same. However, when the battery powder contains manganese, it may not be necessary to add a manganese-containing substance to the first leachate. Through contact between the battery powder and the first leachate, manganese in the battery powder is leached out at an early stage, and the first leachate becomes one that contains manganese ions. As will be described later, when a post-second leaching solution obtained in a second leaching step is used as the first leachate in the first leaching step, manganese ions contained in the post-second leaching solution can also be contained in the first leachate.

[0038] When the first leachate contains manganese ions, a reaction in which manganese ions precipitate as manganese oxides such as manganese dioxide (MnO₂) occurs in the first leachate. Along with this manganese precipitation reaction, the metal oxide of the target metal in the battery powder is reduced, and the target metal is leached into the first leachate. The manganese precipitation reaction and the reduction reaction of nickel and cobalt are, for example, Mn 2+ +NiO₂→MnO₂+Ni 2+ , Mn 2+ +CoO₂→MnO₂+Co 2+ can be represented by Other oxides exceeding divalency can also be reduced with divalent manganese ions in the same manner. Note that copper that may be contained in the battery powder may also be leached out here.

[0039] At this time, for example, a reducing agent such as hydrogen peroxide may be added for the purpose of adjusting to a predetermined oxidation-reduction potential to facilitate the manganese precipitation reaction. However, compared with a case where the target metal in the metal oxide is leached only with a reducing agent, the usage amount of the reducing agent can be greatly reduced.

[0040] However, adding a certain amount of reducing agent may lower the oxidation-reduction potential, potentially creating conditions that make the manganese deposition reaction less likely to occur. Furthermore, avoiding excessively high oxidation-reduction potential is also important from the perspective of making more effective use of the manganese deposition reaction. Specifically, in the first leaching step, it is preferable to set the oxidation-reduction potential (based on silver / silver chloride potential) of the first leaching solution to 1000 mV to 1300 mV, and more preferably to 1100 mV to 1200 mV.

[0041] Furthermore, since the pH changes depending on the amount of acid used, it is important to adjust the pH in the first leaching step in order to ensure that the manganese precipitation reaction occurs effectively. In the first leaching step, the pH of the first leaching solution is preferably -1 to 4, and more preferably 0 to 2.

[0042] As illustrated in Figure 3, in the potential-pH diagram (Pourbet diagram), the region where manganese deposition reactions are likely to occur (the region where MnO2 exists in Figure 3) may have a lower oxidation-reduction potential as the pH increases. In the first leaching step, it is desirable to adjust the pH and oxidation-reduction potential of the first leaching solution to fall within such a region, depending on various conditions. In this embodiment, by leaching the target metal in two stages, the first and second leaching steps, the amount of acid used in the first leaching step can be kept relatively low, and the pH tends to be relatively high. Therefore, when a reducing agent is used in the first leaching step, even if the oxidation-reduction potential is slightly lowered by the addition of the reducing agent, the manganese deposition reaction can be effectively carried out. Figure 3 shows the region where manganese deposition reactions are likely to occur by superimposing potential-pH diagrams derived from the Nernst equation, etc., for each elemental metal and oxide. As shown in Figure 3, the boundary between the dissolution or precipitation of Mn at a predetermined temperature such as 70°C is determined by the redox potential E (mV, relative to silver / silver chloride potential), pH, and manganese ion concentration C. Mn From (mol / L), the formula is: E = 1.228 - 0.1182 × pH - 0.0295 × log(C) Mn It can be expressed as ) - 0.17. For example, E ≥ 1.228 - 0.1182 × pH - 0.0295 × log(C Mn), the oxidation-reduction potential and pH may be set to be -0.17.

[0043] In the first leaching step, a part of the target metal in the metal oxide contained in the battery powder is leached out by a manganese precipitation reaction in the first leachate, and the remainder exists as a solid. Therefore, when solid-liquid separation is performed after leaching a part of the target metal, some metal ions of the target metal (Ni 2+ and / or Co 2+ ) and a first leaching residue containing the solid remainder of the target metal (such as NiO2 and / or CoO2) and manganese oxide (such as MnO2) can be obtained. When the manganese oxide generated by the manganese precipitation reaction contains manganese dioxide, the first leaching residue will contain manganese dioxide. The solid-liquid separation can be carried out by known devices and methods such as a filter press or a thickener, and the same applies to the solid-liquid separation in the second leaching step.

[0044] Among the first post-leaching solution and the first leaching residue obtained in the first leaching step, the first post-leaching solution, as a metal-containing solution in which the target metal is leached, can be sent to a subsequent step for use in removing impurities and recovering the metal. Since the first leaching residue that remains undissolved in the first leaching step contains the target metal, it is supplied to the second leaching step described below in order to leach out the target metal.

[0045] It is preferable that the first post-leaching solution contains substantially no manganese ions from the viewpoint of reducing the load required for removing manganese in the subsequent step. Specifically, it is suitable that the manganese ion concentration of the first post-leaching solution is 2000 mg / L or less. In order to obtain such a first post-leaching solution with the above manganese ion concentration, the end timing of leaching a part of the target metal can be determined based on the manganese ion concentration in the first leachate or the leaching rate of manganese.

[0046] In the second leaching step, the above first leaching residue is brought into contact with an acidic second leachate containing sulfuric acid, hydrochloric acid, nitric acid or other acids, to leach the target metal in the first leaching residue into the second leachate. Subsequent solid-liquid separation is performed to obtain a second post-leaching solution containing metal ions of the target metal (Ni 2+ and / or Co 2+ ).

[0047] When the first leaching residue is brought into contact with the second leaching solution, a reducing agent containing hydrogen peroxide (H2O2) may be added for the purpose of leaching as much of the target metal as possible from the first leaching residue. In this case, for example, NiO2 + H2O2 + 2H + →Ni 2+ +2H2O+O2, CoO2+H2O2+2H + →Co 2+ Based on reaction equations such as +2H2O + O2, the metal oxide is reduced in the second leaching solution, and the target metal is effectively leached out. Preferably, hydrogen peroxide can be added in excess, in amounts greater than the molar equivalents used in the reaction with nickel and cobalt, in order to leach out much or all of the target metal in the first leaching residue.

[0048] If an excess of hydrogen peroxide is added to the second leaching solution during the second leaching process, the hydrogen peroxide will be preferentially consumed in the leaching of the target metal. However, the remaining hydrogen peroxide after leaching may dissolve the manganese oxide in the first leaching residue. The reaction in this case is MnO2 + H2O2 + 2H + →Mn 2+ It can be represented as +2H2O+O2. Excessive addition of hydrogen peroxide lowers the redox potential, and in the potential-pH diagram of Figure 3, the lower Mn 2+ This can be a region where metal ions (Ni) of the target metal exist. 2+ and / or Co 2+ In addition to manganese ions (Mn 2+ A second exudate containing ) is obtained.

[0049] As shown in Figure 1, the second leaching solution is used as part of the first leaching solution in the next leaching process. If the second leaching solution contains manganese ions, these manganese ions can be used in the manganese deposition reaction in the first leaching process. This is useful when the amount of manganese ions in the newly used first leaching solution or the manganese in the newly added battery powder is not sufficient for the reduction of metal oxides by the manganese deposition reaction. Furthermore, if at least a portion of the manganese oxide in the first leaching residue remains undissolved in the second leaching process, the second leaching residue obtained in the second leaching process will contain manganese oxide (such as MnO2).

[0050] Unlike the first leaching step, the second leaching step is not intended to induce a manganese precipitation reaction, and therefore is not limited to the oxidation-reduction potential and pH conditions that would cause a manganese precipitation reaction. The pH of the second leaching solution in the second leaching step is preferably -1 to 2, and more preferably 0 to 1. If the pH is too high in the second leaching step, cobalt and nickel may not dissolve completely, and if it is too low, there is a concern that cobalt and nickel crystals may precipitate. Furthermore, the oxidation-reduction potential (based on silver / silver chloride potential) of the second leaching solution in the second leaching step is preferably 900 mV to 1150 mV, and more preferably 1000 mV to 1150 mV. If the oxidation-reduction potential is too high in the second leaching step, there is a possibility that the dissolution of nickel and cobalt will not be completed, and if it is too low, there is a concern that only manganese will dissolve.

[0051] The second leaching solution obtained in the second leaching step may contain cobalt ions at a concentration of 0.1 g / L to 30 g / L, and / or nickel ions at a concentration of 0.1 g / L to 30 g / L, and may also contain manganese ions at a concentration of 0.1 g / L to 15 g / L, lithium ions at a concentration of 0.01 g / L to 10 g / L, iron ions at a concentration of 0.1 g / L to 10 g / L, aluminum ions at a concentration of 0.01 g / L to 10 g / L, and copper ions at a concentration of 0.01 g / L to 10 g / L.

[0052] The leaching process, including the first and second leaching steps described above, is repeated multiple times. In this case, the second leaching solution obtained in the second leaching step of the previous leaching process is used as part of the first leaching solution in the first leaching step of the next leaching process. In this way, the metal ions of the target metal that were contained in the second leaching solution of the previous leaching process are included in the first leaching solution after the first leaching step of the next leaching process in the same form, thereby improving the leaching rate and recovery rate of the target metal. In addition to the metal ions of the target metal that were contained in the second leaching solution of the previous leaching process, this first leaching solution also contains metal ions of the target metal derived from the battery powder added in the next leaching process.

[0053] The first leaching solution, which contains metals, may have, for example, a cobalt ion concentration of 1 g / L to 50 g / L and / or a nickel ion concentration of 1 g / L to 50 g / L. Furthermore, the first leaching solution may have a lithium ion concentration of 1 g / L to 20 g / L, an iron ion concentration of 0.1 g / L to 5 g / L, an aluminum ion concentration of 0.1 g / L to 10 g / L, and a copper ion concentration of 0.1 g / L to 10 g / L.

[0054] By repeatedly performing multiple leaching processes in this manner, the amount of reducing agent used can be reduced or eliminated compared to a single leaching process, while the leaching rate of the target metal can be increased. As a result of reducing the use of reducing agents, the cost required for metal leaching can be reduced.

[0055] If we were to attempt to extract as much NiO2, CoO2, etc., from the battery powder as possible using a single leaching process, the following disadvantages would arise. It should be noted here that the leaching of NiO2, CoO2, etc., requires a reaction equivalent amount of reducing agent.

[0056] Firstly, in a single leaching process, if the amount of Mn ions in the leached solution is less than the molar equivalent required to reduce the total amount of NiO2, CoO2, etc., adding hydrogen peroxide as a reducing agent to compensate for the deficiency will lower the redox potential, causing it to move outside the region where the manganese deposition reaction occurs (as shown in Figure 3). As a result, manganese will not precipitate, and the manganese ions will no longer act as a reducing agent. Therefore, there is a trade-off between the occurrence of the manganese deposition reaction and the leaching of more Ni and Co. It is difficult to adjust the conditions so that both can be achieved in a single leaching process.

[0057] Secondly, the composition of battery powder varies, sometimes resulting in a small amount of manganese ions being generated from the powder, or a large amount of NiO2, CoO2, etc., that need to be reduced for leaching. If we were to attempt to leach all of NiO2, CoO2, etc. in a single leaching process, taking such variations into account, we would have to add a slightly excessive amount of hydrogen peroxide as a reducing agent. However, as mentioned above, adding an excessive amount of hydrogen peroxide lowers the oxidation-reduction potential, preventing manganese from precipitation and rendering the manganese ions ineffective as a reducing agent.

[0058] In contrast, the embodiment described above involves a first leaching step in which the target metal is mainly leached out by a manganese deposition reaction, and a second leaching step in which any remaining target metal after the first leaching step is leached out. In other words, the manganese deposition reaction and the leaching of a large amount of target metal, which are in a trade-off relationship, are divided into a first leaching step and a second leaching step. In this case, because there is a second leaching step, it is not necessary to leach out all of the target metal in the first leaching step, and the conditions can be set to cause the manganese deposition reaction to occur. Thus, this embodiment can be said to have resolved the disadvantages of a single leaching step as described above.

[0059] (Method for recovering metals) After removing impurities from the metal-containing solution obtained by the metal leaching method described above, a process for recovering metals such as cobalt and nickel can be carried out. For example, impurity removal can be done by removing some aluminum and iron by neutralization, or by removing the remainder of aluminum and manganese by solvent extraction. For metal recovery, cobalt and nickel can be sequentially extracted by solvent extraction, and then recovered by back-extraction. Furthermore, lithium can be recovered from the extractive solution after the extraction of cobalt and nickel by various methods. For example, if the extractive solution is a lithium sulfate solution, a lithium hydroxide solution can be prepared from the lithium sulfate solution, and lithium hydroxide can be crystallized from it.

[0060] Next, we conducted tests to verify the effectiveness of the metal leaching method described above, which are explained below. However, this explanation is for illustrative purposes only and is not intended to be an exhaustive list.

[0061] (Test Example 1) 10 g of positive electrode active material containing manganese, cobalt, nickel, and lithium in the amounts (mass%) shown in Table 1 was added to a sulfuric acid solution prepared by adding 95% pure sulfuric acid to 100 ml of pure water. The solution was stirred at a stirring speed of 250 rpm for 3 hours at a leaching temperature of 60°C to leach each metal. The amount of sulfuric acid added was 1 / 2 molar amount of the amount of hydrogen ions required for the leaching of manganese, cobalt, nickel, and lithium, assuming that 1 times the amount of hydrogen ions for lithium and 2 times the amount for manganese, cobalt, and nickel are required to leach manganese, cobalt, nickel, and lithium from the positive electrode active material.

[0062]

[0063] Then, the above leaching process was carried out by varying the amount of hydrogen peroxide (35% purity) added relative to the amount of sulfuric acid (95% purity), and the relationship between the amount of hydrogen peroxide added and the leaching rate of each metal was investigated by comparing the leaching rates of each metal three hours after the start of leaching. The results are shown in Figure 4. From the graph in Figure 4, it can be seen that the smaller the ratio of hydrogen peroxide added to the amount of sulfuric acid added, the lower the manganese leaching rate and the more manganese precipitates.

[0064] Furthermore, 10 g of the positive electrode active material shown in Table 1 was added to 100 ml of pure water and a sulfuric acid solution with a 1:1 molar equivalent of sulfuric acid, and the mixture was stirred at a stirring speed of 250 rpm for 3 hours at a leaching temperature of 60°C to leach each metal.

[0065] Here, too, the above leaching process was performed by varying the ratio of hydrogen peroxide added to sulfuric acid, and the leaching rate of each metal changed as the leaching time progressed under each condition. The results are shown in Figures 5 to 7.

[0066] As shown in the graphs in Figures 5-7, the manganese leaching rate increases in the initial stages of leaching, but then decreases, while the nickel and cobalt leaching rates increase. The reason for this decrease in the manganese leaching rate is presumed to be that after manganese leached out and became manganese ions, these manganese ions precipitated as solids. Since the nickel and cobalt leaching rates continued to increase even after the manganese leaching rate decreased, it can be seen that the manganese precipitation reaction promoted the leaching of nickel and cobalt. Furthermore, from Figure 7, it can be seen that if the amount of hydrogen peroxide added is large, the manganese leaching rate does not decrease sufficiently, and not much manganese precipitates.

[0067] (Test Example 2) Using battery powder containing each metal in the amounts (mass%) shown in Table 2, the leaching process, including the first leaching stage (first leaching process) and the second leaching stage (second leaching process) shown in Figure 8, was performed for two cycles.

[0068]

[0069] In all cycles, in the first leaching stage, the pulp concentration was set to 100 g / L, and 95% pure sulfuric acid and 35% pure hydrogen peroxide were added to the main metals in the battery powder (Co, Ni, Mn, Li, Cu, Fe, and Al) to set the pH to 0.3 for leaching. The amount of sulfuric acid added was set to 1.5 / 2 times the molar amount of hydrogen ions required for leaching Co, Ni, Mn, Li, Cu, Fe, and Al from the battery powder, assuming that 1 times the amount of hydrogen ions is needed for Li, 2 times for Co, Ni, Mn, Cu, and 3 times for Fe and Al. The volume ratio of hydrogen peroxide (35% purity) added to sulfuric acid (95% purity) was set to 0.13. In the second leaching stage, the pulp concentration was set to 200 wet g / L (concentration based on the wet mass of the residue from the first leaching stage), and sulfuric acid and hydrogen peroxide were added to adjust the pH to a range of 0.3 to 0.5.

[0070] In the first leaching stage of the first cycle, the manganese ion concentration was 1.3 g / L after 3 hours and 0.052 g / L after 6 hours. This suggests that manganese precipitated, and the process proceeded to the second leaching stage. In the second leaching stage, hydrogen peroxide was added to lower the ORP. At an ORP of 1150 mV, the Mn concentration was 0.4 g / L; at an ORP of 1130 mV, it was 1.1 g / L; and at an ORP of 1110 mV, it was 2.1 g / L. Once manganese leaching was confirmed, the residue was analyzed to confirm that cobalt and nickel were sufficiently dissolved. The residue consisted of 1.0 mass% Co, 0.1 mass% Ni, and 59 mass% Mn. The Co leaching rate was 98.3%, and the Ni leaching rate was over 99%. Note that ORP is defined as vs. It is Ag / AgAl.

[0071] In the second cycle, during the first leaching stage, the Mn concentration decreased from 1.8 g / L after 3 hours to 0.17 g / L after 6 hours and to 0.076 g / L after 7 hours. In the second leaching stage, hydrogen peroxide was added to lower the ORP, resulting in Mn concentrations of 0.8 g / L at an ORP of 1150 mV, 2.0 g / L at an ORP of 1130 mV, and 3.7 g / L at an ORP of 1110 mV. The residue consisted of 0.8 mass% Co, 0.08 mass% Ni, and 60 mass% Mn, with a Co leaching rate of 98.7% and a Ni leaching rate of over 99%.

[0072] Figures 9 and 10 show the changes in Mn concentration relative to ORP during the first and second leaching stages in each cycle. From Figure 9, it can be seen that in the first leaching stage, after adding a predetermined amount of hydrogen peroxide, the ORP increased and the Mn concentration decreased accordingly, indicating that manganese dissolved once, and then the manganese precipitation reaction proceeded, resulting in the deposition of manganese. On the other hand, in the second leaching stage shown in Figure 10, when hydrogen peroxide was added until the ORP reached 1130 mV to 1100 mV, it can be seen that as the ORP decreased, manganese dissolved along with cobalt and nickel, causing the Mn concentration to increase.

[0073] Note that the distribution ratios of each metal in the liquid after the first leaching stage and the residue after the second leaching stage shown in Figure 8 represent the proportion of each metal to the battery powder introduced in that cycle. Therefore, the distribution ratio of each metal may not add up to 100% because some metals in the liquid after the second leaching stage are sent to the next cycle, and some metals are carried over from the previous cycle.

[0074] Based on the above, it was suggested that the aforementioned metal leaching method may allow for effective leaching of the target metal using a relatively small amount of reducing agent or without using any reducing agent at all.

[0075] (Potential contribution to the SDGs) According to the embodiment described above, the target metal can be effectively leached using a relatively small amount of reducing agent or without using any reducing agent, which may contribute to reducing processing costs in the recovery of metals from lithium-ion battery waste. 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).

Claims

1. A method for leaching at least one target metal from battery powder containing at least one of cobalt and nickel as a metal oxide, comprising: a first leaching step in which the battery powder is brought into contact with an acidic first leaching solution to leach a portion of the target metal from the metal oxide contained in the battery powder into the first leaching solution, and at least a portion of the manganese ions contained in the first leaching solution to precipitate as manganese oxide, thereby obtaining a first post-leaching solution containing a portion of the target metal as metal ions, and a first leaching residue containing the remaining solid portion of the target metal and the manganese oxide; and a second leaching step in which the first leaching residue is brought into contact with an acidic second leaching solution to leach the target metal from the first leaching residue into the second leaching solution, thereby obtaining a second post-leaching solution containing the target metal as metal ions, wherein the leaching process is repeated multiple times, and in each of the multiple leaching processes, the second post-leaching solution from the previous leaching process is used as at least a portion of the first leaching solution in the next leaching process. A metal leaching method comprising, at least the first post-leaching solution being a metal-containing solution from which the target metal has been leached.

2. The metal leaching method according to claim 1, wherein in the second leaching step, the manganese oxide in the first leaching residue is dissolved to obtain the second post-leaching solution containing manganese ions.

3. The metal leaching method according to claim 1, wherein the battery powder contains manganese as a metal oxide, and in the first leaching step, the manganese in the battery powder leaches into the first leaching solution so that the first leaching solution contains manganese ions.

4. The metal leaching method according to claim 3, wherein the battery powder contains cobalt and / or nickel and manganese as a composite metal oxide and / or each as a single metal oxide.

5. The metal leaching method according to claim 1, wherein the battery powder used is one in which the amount of manganese is less than the total amount of nickel and cobalt.

6. The metal leaching method according to claim 1, wherein in the first leaching step, the pH of the first leaching solution is set to -1 to 4 and the oxidation-reduction potential (based on silver / silver chloride potential) is set to 1000 mV to 1300 mV.

7. The metal leaching method according to claim 1, wherein in the second leaching step, the pH of the second leaching solution is set to -1 to 2 and the oxidation-reduction potential (based on silver / silver chloride potential) is set to 900 mV to 1150 mV.

8. The metal leaching method according to claim 1, wherein a reducing agent is added to the second leaching solution in the second leaching step.

9. The metal leaching method according to claim 8, wherein the reducing agent contains hydrogen peroxide (H2O2).

10. The metal leaching method according to claim 1, wherein the manganese oxide in the first leaching residue contains manganese dioxide (MnO2).

11. The metal leaching method according to claim 1, wherein the manganese ion concentration of the first leaching solution is 2000 mg / L or less.

12. A method for recovering a metal from a metal-containing solution obtained by the metal leaching method according to any one of claims 1 to 11.

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