WO2025099984A1 - Metal recovery method - Google Patents

Abstract

Provided is a method for recovering metal from lithium ion battery waste, the method including: a preprocessing step in which preprocessing that includes heat treatment of the lithium ion battery waste is performed to obtain an aluminum-containing intermediate that contains aluminum and lithium; a lithium leaching step in which the aluminum-containing intermediate is brought into contact with a liquid to cause the lithium in the aluminum-containing intermediate to leach into the liquid, the pH of the liquid after the lithium leaching is complete is brought to 7–13, and a residue and a lithium-containing solution are obtained; an alkali leaching step in which the residue from the lithium leaching step is brought into contact with an alkaline solution to cause the aluminum in the residue to leach into the alkaline solution and a residue and an aluminum-containing solution are obtained; and wet processing in which metal in a battery powder that includes the residue from the alkali leaching step is caused to leach and metal ions are separated from a metal-containing solution into which the metal has dissolved. The lithium-containing solution obtained in the lithium leaching step is used in the wet processing.

Description

Metal recovery method

This specification describes a method for recovering metals from lithium-ion battery waste.

Vehicles such as hybrid cars, fuel cell cars, and electric cars are equipped with on-board battery packs that supply power to electric motors as a drive source (see, for example, Patent Documents 1 to 6). In on-board battery packs, battery cells may be housed inside a frame that forms the skeleton of the exterior. Many on-board battery packs are constructed by bundling multiple battery cells into a battery module, and then connecting multiple battery modules together. On-board battery packs may also include a BMS (Battery Management System) that monitors each battery cell, a cooling device that cools the battery, and wires that connect them.

　The battery cells in the above-mentioned vehicle battery packs generally use secondary batteries, particularly nickel-metal hydride batteries, which can be charged to store electricity and used repeatedly, but in recent years, lithium-ion batteries that use lithium transition metal composite oxides for the positive electrode have come to be used. Such vehicle lithium-ion batteries contain valuable metals such as cobalt. Therefore, from the perspective of effective resource utilization, when vehicle lithium-ion batteries are discarded after use, it is desirable to easily recover the valuable metals that may be contained in the lithium-ion battery waste at a relatively low cost in order to reuse them.

Incidentally, the process of recovering valuable metals from waste lithium-ion batteries, not limited to those used in vehicles, can include, for example, roasting the waste lithium-ion batteries or other specified pretreatment, and wet processing the battery powder obtained after the pretreatment.

Specifically, in the wet treatment, 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 the metals are dissolved. Next, as described in Patent Document 7, for example, aluminum ions, iron ions, manganese ions, and the like are removed from the metal-containing solution sequentially or simultaneously by neutralization or solvent extraction. After that, the cobalt ions and nickel ions in the metal-containing solution are separated by solvent extraction. After the nickel ions are separated by extraction, a metal-containing solution in which lithium ions remain is obtained.

JP 2006-179190 A JP 2007-172938 A US Patent Application Publication No. 2007/0141454 JP 2007-172939 A US Patent Application Publication No. 2007/0141455 JP 2011-198713 A International Publication No. 2018/181816

It is desirable to remove the aluminum in lithium-ion battery waste by pretreatment, but when trying to recover as much cobalt, nickel, etc. as possible, some of the aluminum may not be removed by pretreatment and may be included in the battery powder together with the cobalt, nickel, etc. In this case, when the metals in the battery powder are leached with acid, the aluminum is leached together with other metals such as cobalt and nickel, and is included in the metal-containing solution as aluminum ions. When a relatively large amount of aluminum ions are contained in the metal-containing solution, it becomes difficult to remove them sufficiently. Therefore, it is desirable to remove the aluminum before leaching the battery powder with acid.

On the other hand, if you try to remove the aluminum before acid leaching, lithium may be removed along with the aluminum, resulting in a loss of lithium.

This specification provides a metal recovery method that utilizes lithium while suppressing lithium loss and effectively removes aluminum.

The metal recovery method disclosed in this specification is a method for recovering metals from lithium ion battery waste, and includes a pretreatment step of subjecting the lithium ion battery waste to a pretreatment step including a heat treatment to obtain an Al-containing intermediate containing aluminum and lithium, a lithium leaching step of contacting the Al-containing intermediate with a liquid to leach the lithium in the Al-containing intermediate into the liquid, setting the pH of the liquid at the end of the lithium leaching to 7 to 13, and obtaining a residue and a lithium-containing solution, an alkaline leaching step of contacting the residue from the lithium leaching step with an alkaline solution to leach the aluminum in the residue into the alkaline solution, obtaining a residue and an aluminum-containing solution, and a wet treatment step of leaching the metal in the battery powder containing the residue from the alkaline leaching step and separating metal ions from the metal-containing solution in which the metal has been dissolved, and the lithium-containing solution obtained in the lithium leaching step is used in the wet treatment.

The above-mentioned metal recovery method makes it possible to utilize lithium while minimizing lithium loss, and also to effectively remove aluminum.

FIG. 1 is a flow diagram showing an example of a process including a metal recovery method according to one embodiment. FIG. 2 is a flow diagram showing another example of a process including a metal recovery method according to one embodiment. FIG. 3 is a flow diagram showing an example of a process carried out on the battery powder obtained by the process of FIG. 1 or 2. 1 is a graph showing the change over time in the leaching rate of each metal in the lithium leaching of Example 1. 1 is a graph showing the change in leaching rate of each metal and pH over time in the alkali leaching of Example 1.

Hereinafter, an embodiment of the above-mentioned metal recovery method will be described in detail.
One embodiment of the metal recovery method is a method for recovering metals from lithium ion battery waste. This method includes a pretreatment step of subjecting lithium ion battery waste to a pretreatment including a heat treatment to obtain an Al-containing intermediate containing aluminum and lithium, a lithium leaching step of contacting the Al-containing intermediate with a liquid to leach lithium in the Al-containing intermediate into the liquid, adjusting the pH of the liquid at the end of the lithium leaching to 7 to 13, and obtaining a residue and a lithium-containing solution, an alkaline leaching step of contacting the residue from the lithium leaching step with an alkaline solution to leach aluminum in the residue into the alkaline solution, and obtaining a residue and an aluminum-containing solution, and a wet treatment of leaching metals in battery powder containing the residue from the alkaline leaching step and separating metal ions from the metal-containing solution in which the metals have been dissolved.

In order to remove the aluminum from the Al-containing intermediate, it is effective to leach the aluminum by contacting it with an alkaline solution before the acid leaching process. However, when the Al-containing intermediate is brought into contact with an alkaline solution, not only the aluminum in the Al-containing intermediate but also the lithium is leached into the alkaline solution, resulting in a loss of lithium.

In contrast, in this embodiment, a lithium leaching process is carried out before the alkaline leaching process, and lithium is separated and recovered to a certain extent from the Al-containing intermediate in advance in the lithium leaching process. As a result, in the subsequent alkaline leaching process, the amount of lithium leached into the alkaline solution can be reduced compared to when the alkaline leaching process is carried out without going through the lithium leaching process.

Then, the lithium-containing solution obtained in the lithium leaching process is used in the wet treatment. This allows the lithium separated in the lithium leaching process to be effectively utilized, for example, by the lithium in the lithium-containing solution contributing to an increase in the lithium ion concentration in the liquid during the wet treatment.

To recover metals from battery powder, wet processing is performed as shown in Figure 3. In wet processing, the battery powder is subjected to a preliminary leaching process if necessary, followed by an acid leaching process in which the battery powder is leached with acid to obtain a metal-containing solution containing various metal ions. For the metal-containing solution from which the metal ions are separated, a neutralization process and a recovery process can be performed in this order. The processes following the acid leaching process in wet processing are also referred to as a series of processes. Here, each process will be explained according to Figures 1 to 3. However, the flows in Figures 1 to 3 are examples and are not limited to these.

(Lithium ion battery waste)
Lithium-ion battery waste can be various in-vehicle lithium-ion batteries that can be installed in vehicles such as hybrid cars, fuel cell cars, and electric cars, and that are discarded due to the scrapping of the vehicle, battery replacement, manufacturing defects, or other reasons. However, it is not limited to in-vehicle lithium-ion battery waste, and can include various lithium-ion battery waste for other purposes. Lithium-ion battery waste refers to lithium-ion batteries that are subject to recycling, and it does not matter whether the lithium-ion batteries are traded for a value, or traded free of charge or as industrial waste.

The lithium ion batteries contained in such lithium ion battery waste include a positive electrode material, a negative electrode material, an electrolyte, and an aluminum case around them. Here, the positive electrode material and the negative electrode material can be respectively formed by fixing a positive electrode active material or a negative electrode active material to a positive electrode current collector such as aluminum foil or a negative electrode current collector such as copper foil, for example, with polyvinylidene fluoride (PVDF) or other organic binders. Of these, the positive electrode active material is, for example, a single metal oxide of lithium, nickel, cobalt, and manganese, or a composite metal oxide of two or more of them. Examples of such positive electrode active materials include LiCoO ₂ , LiNiO ₂ , Li-Co-Ni-O ₂ , and Li-Co-Ni-Mn-O. It is desirable to recover the metal contained in the positive electrode active material as a valuable metal in terms of effective utilization of resources. The metals contained in the positive electrode active material may change form from the oxides described above by heat treatment or the like described below, but regardless of the form, the metals derived from the positive electrode active material, such as cobalt, nickel, and lithium (hereinafter also referred to as "positive electrode-derived metals"), are the subject of recovery here. Note that carbon-based materials are often used as negative electrode active materials, and electrolytic solutions such as ethylene carbonate or diethyl carbonate are often used as electrolytes. In addition, waste lithium-ion batteries for vehicles may contain terminals containing copper and/or iron, iron cases, stainless steel cases, etc.

Waste lithium-ion batteries for vehicles have a metal frame such as iron as the exterior skeleton, and lithium-ion battery cells are housed inside the frame. This type of lithium-ion battery waste often contains multiple battery cells, which are bundled together to form a battery module, and are further configured by connecting multiple battery modules together. In addition, lithium-ion battery waste may also include a BMS (Battery Management System) that monitors each battery cell, a cooling device that cools the battery, and wires that connect them. The wires are made of a metal containing copper, such as copper (Cu wire), and are connected to each battery cell and the BMS to transmit information (temperature, voltage, etc.) related to the temperature and voltage of each battery cell to the BMS. In addition, resin members may be provided between and around the battery cells.

Furthermore, the casing of lithium-ion battery waste usually contains an electrolyte solution in which an electrolyte such as lithium hexafluorophosphate is dissolved in an organic solvent. For example, ethylene carbonate, diethyl carbonate, etc. may be used as the organic solvent.

In some of this lithium ion battery waste, the positive electrode active material is difficult to separate from the aluminum foil. In contrast, in this embodiment, as described below, an alkaline leaching process is performed, which can reduce the amount of aluminum ions mixed into the metal-containing solution obtained after the acid leaching process. Furthermore, if a pretreatment process as described below is performed, such aluminum can be removed more effectively. In particular, for waste from lithium ion batteries in which the positive electrode active material does not separate from the aluminum foil even after re-crushing as described below in the pretreatment process, it is effective to perform the alkaline leaching process of this embodiment.

(Pretreatment process)
In the pretreatment process, at least a heat treatment is performed on the lithium ion battery waste. In many cases, the pretreatment process includes heat treatment, crushing, and sieving in this order or in any order. In the example shown in Fig. 1, heat treatment, crushing, and sieving are performed in this order. In the example shown in Fig. 2, after heat treatment, crushing, and sieving are performed in order, small-diameter sieved matter, medium-diameter sieved matter, and large-diameter sieved matter with different particle sizes are obtained by sieving, and the medium-diameter sieved matter and large-diameter sieved matter are further treated. Here, with regard to the classification of the small-diameter sieved matter, the medium-diameter sieved matter, and the large-diameter sieved matter based on particle size, when sieving using a sieve having lattice-shaped sieve holes with a predetermined side length, the sieved matter that falls on the sieve has a particle size equal to or larger than the predetermined side length of the sieve holes, and the sieved matter that falls on the sieve has a particle size less than the predetermined side length of the sieve holes. After the pretreatment step, a battery powder is obtained.

In the example shown in Figures 1 and 2, the steps are performed in the order of heat treatment, crushing, and sieving. However, for example, the order may be crushing, heat treatment, and sieving, although not shown. In other words, in this embodiment, it is sufficient to perform pretreatment including heat treatment on the lithium ion battery waste, and the heat treatment may be performed after the lithium ion battery waste is subjected to treatment other than heat treatment. Furthermore, treatment other than heat treatment, crushing, and sieving may be included in the pretreatment process, such as when the lithium ion battery waste is disassembled and then heat treatment, crushing, and sieving are performed. In the following, for convenience of explanation, an example will be described in which heat treatment, crushing, and sieving are performed in the order shown in Figures 1 and 2.

Note that battery powder refers to a powder in which the positive electrode material components are separated and concentrated by performing some kind of processing on lithium ion battery waste. Battery powder can be obtained as a powder in which the positive electrode material components are concentrated by performing heat treatment on lithium ion battery waste and, if necessary, further crushing and sieving. In this embodiment, the residue obtained after the alkaline leaching process described below also becomes battery powder.

The heat treatment is performed for the purpose of removing the electrolyte in the lithium ion battery waste. In the heat treatment, the temperature is not particularly important as long as the lithium ion battery waste is heated. In the heat treatment, the lithium ion battery waste may be heated to a temperature at which the electrolyte can be removed, for example, a relatively low temperature of about 100°C or 200°C (for example, 100°C or higher, typically 100°C to 185°C or 185°C to 350°C). In the low-temperature heating, the electrolyte evaporates, and lithium hexafluorophosphate, lithium fluoride generated by decomposition of lithium hexafluorophosphate, etc. may remain. Since lithium hexafluorophosphate and lithium fluoride are water-soluble and leach into an alkaline solution, it is desirable to perform a lithium leaching process before the alkaline leaching process as in this embodiment to recover lithium in lithium hexafluorophosphate and lithium fluoride. In addition, after or without heating the lithium ion battery waste at a low temperature, 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 hour to 8 hours. In the high temperature heating, _LiCoO2 in the positive electrode active material may be decomposed to produce cobalt oxide, metallic cobalt, lithium carbonate, etc. By such heat treatment, cobalt, nickel, etc. in the positive electrode active material in the lithium ion battery waste may be converted into a predetermined form exhibiting magnetism. Note that the composition of the positive electrode active material changes due to heat treatment, but even if it has been subjected to heat treatment, it may be called a positive electrode active material here.

In the heat treatment, for example, heating may be performed in an air atmosphere or an inert atmosphere, but is not limited thereto and various atmospheres can be used. The heat treatment may be performed in a reduced pressure atmosphere such as a vacuum. Heating in an air atmosphere and heating in an inert atmosphere may both be performed in any order. Preferably, after heating in an inert atmosphere, the atmosphere is switched and heating is further performed in an air atmosphere. The heat treatment furnace is not particularly limited, but for example, an atmospheric and vacuum electric furnace or an atmospheric muffle furnace can be used for a batch type, or a roller hearth kiln or mesh belt kiln can be used for a continuous type.

After the heat treatment, if necessary, certain parts are removed from the lithium-ion battery waste, and the lithium-ion battery waste is then crushed. This crushing process destroys the battery cell casings and separates the positive electrode-derived metals, such as nickel and cobalt, from the aluminum foil to obtain crushed material.

A variety of known crushers can be used here, but specific examples include impact crushers that apply impact while cutting the case and battery, such as a sample mill, hammer mill, pin mill, wing mill, tornado mill, and hammer crusher. A screen can be installed at the outlet of the crusher, so that the batteries are discharged from the crusher through the screen when they have been crushed to a size that can pass through the screen.

The crushed material obtained by the above crushing is subjected to sieving, whereby it is sieved according to its size and separated into multiple types of sieved material with different particle sizes. In the example shown in Figure 1, the sieved material obtained by sieving is an Al-containing intermediate material, which is subjected to a lithium leaching process and an alkaline leaching process, and the residue from the alkaline leaching process is battery powder B. On the other hand, the under-sieved material may contain almost no aluminum but metals derived from the positive electrode, in which case the under-sieved material can be battery powder A. Battery powders A and B are subjected to an acid leaching process, from which metals can be recovered.

In the example shown in Figure 2, the crushed material is sieved to obtain at least small, medium and large sieved matter with different particle sizes. In Figure 2, the crushed material is divided into three types, but it is also possible to divide it into four or more types of sieved matter including the small, medium and large sieved matter. Of these, the small sieved matter, which has a relatively small particle size, may contain positive electrode-derived metals without substantially containing aluminum, and can be subjected to the acid leaching process as battery powder A.

The medium-sized sieved material may contain aluminum as well as metals derived from the positive electrode, and as described below, eddy current sorting may be performed as necessary to extract the magnetized material (Al-containing intermediate), after which the lithium leaching process and alkaline leaching process may be performed. However, this eddy current sorting may be omitted, in which case the medium-sized sieved material is subjected to the lithium leaching process and alkaline leaching process as an Al-containing intermediate. The residue after this alkaline leaching process becomes battery powder B. Alternatively, the lithium leaching process and alkaline leaching process may be omitted, and the medium-sized sieved material or the magnetized material after eddy current sorting may be used as battery powder B.

For the large-diameter sieved material, which often contains aluminum and metals derived from the positive electrode, it is preferable to further perform magnetic separation, re-crushing, and re-sieving to obtain an under-sieved material from which as much aluminum as possible has been separated. The under-sieved material obtained by re-sieving can be fed into the acid leaching process as battery powder C. Meanwhile, the over-sieved material obtained by re-sieving is subjected to the lithium leaching process and the alkaline leaching process. The residue after the alkaline leaching process becomes battery powder D. If the lithium-ion battery waste contains a certain amount of copper or aluminum, most of that copper and aluminum will be distributed in the over-sieved material obtained by re-sieving.

By carrying out the above-mentioned processes (crushing and sieving, eddy current sorting for medium-sized sieved material, magnetic sorting for large-sized sieved material, re-crushing and re-sieving) to dry-process and remove as much aluminum as possible from the Al-containing intermediates that are to be subjected to the lithium leaching process and alkaline leaching process described below, it is possible to reduce the amount of chemicals required for the alkaline solution in the alkaline leaching process, and therefore the cost of those chemicals.

When sieving crushed material to obtain small-, medium-, and large-diameter sieved materials, the mesh size of each sieve can be appropriately set, taking into consideration the following points:

Since the small-diameter sieved material is used as battery powder A as is, it is desirable that it contains few impurities other than the metals to be recovered (iron, aluminum, copper, etc.). When the crushed material is classified by particle size, the crushed material containing these impurities is distributed mostly on the large particle size side. For this reason, if the mesh size of the sieve that separates the small-diameter sieved material from the medium-diameter sieved material is made small to a certain extent, it is possible to prevent the quality of the impurities contained in battery powder A from increasing.

On the other hand, if the medium-sized sieved material is subjected to additional treatments or processes after sieving (eddy current sorting, lithium leaching process, alkali leaching process), the impurities contained in the medium-sized sieved material can be removed by such treatments or processes. However, from the viewpoint of suppressing increases in processing costs, it is desirable to increase the mesh size of the sieve separating the small-sized sieved material from the medium-sized sieved material and reduce the amount of medium-sized sieved material while keeping the quality of impurities contained in the small-sized sieved material (battery powder A) below a specified value. In this way, the mesh size separating the small-sized sieved material from the medium-sized sieved material can be set based on the quality of impurities contained in the small-sized sieved material (battery powder A).

Next, the mesh size of the sieve that separates the medium-sized and large-sized sieved materials can be set based on the iron content of the medium-sized sieved materials. For the large-sized sieved materials, low-force magnetic separation that can remove iron may be performed as described below, whereas low-force magnetic separation is not performed for the medium-sized sieved materials. Furthermore, if the medium-sized sieved materials contain a certain amount of iron, when eddy current separation is performed on the medium-sized sieved materials, the ferromagnetic iron will be included in the magnetized materials to be recovered. Furthermore, as mentioned above, the iron contained in the crushed materials originates from the terminals and casings, and is therefore distributed on the large particle size side. For this reason, it is desirable to appropriately set the mesh size of the sieve that separates the medium-sized and large-sized sieved materials so that the medium-sized sieved materials do not contain more than the allowable amount of iron.

In eddy current sorting, which is performed on the medium-sized sieved material as necessary before the lithium leaching process, non-magnetic conductive materials such as aluminum are removed from the medium-sized sieved material, and magnetic materials containing cobalt, nickel, lithium, etc. are obtained. By removing as much aluminum as possible in this way, the load on the lithium leaching process and the alkaline leaching process can be reduced.

For eddy current sorting, a known eddy current sorting machine can be used, which includes a belt conveyor having a belt for transporting the objects (medium-sized objects in this case) and a pulley around which the belt is wound and driven to rotate. Inside the pulley is a built-in rotor that rotates at high speed to generate a high-frequency alternating magnetic field. The rotor has alternating north and south poles arranged in the circumferential direction, and when it rotates at high speed, an alternating magnetic field is generated. When a non-magnetic conductive object among the objects transported by the belt passes through the alternating magnetic field, an eddy current proportional to the alternating magnetic field is generated in the non-magnetic conductive object, and the magnetic force generated from this current creates a repulsive effect with the magnetic force of the rotor, and the non-magnetic conductive object is separated. Meanwhile, magnetic objects among the objects are basically attached to the belt surface by the magnetic force of the rotor and sent to the lower side of the pulley, and when the effect of the magnetic force weakens, they fall off the belt surface.

The magnetic material separated from the aluminum and other materials by eddy current sorting as described above may be subjected to a lithium leaching process. The non-magnetic conductive material separated from the magnetic material by eddy current sorting contains a relatively large amount of aluminum, and although not shown in the figure, may be subjected to an alkaline leaching process after or without going through the lithium leaching process.

In magnetic separation of the large-diameter sieved material, for example, low magnetic separation using a magnetic force with a relatively low surface magnetic flux density to remove iron from the large-diameter sieved material and/or high magnetic separation using a magnetic force with a relatively high surface magnetic flux density to remove aluminum and the like can be performed. When both low magnetic separation and high magnetic separation are performed, high magnetic separation can be performed after low magnetic separation. However, if the large-diameter sieved material contains almost no iron, low magnetic separation may be omitted. Also, if metallic cobalt and the like are not generated due to the above-mentioned heat treatment being performed at a low temperature and are almost not contained in the large-diameter sieved material, high magnetic separation may be omitted. In low magnetic separation when low-temperature heat treatment is performed, cobalt and the like can be separated into non-magnetic materials. The non-magnetic materials obtained by low magnetic separation of the large-diameter sieved material and/or the magnetic materials obtained by magnetic separation of the high magnetic separation are subjected to re-crushing as described below. In addition, various magnetic separators can be used for magnetic separation as long as they are capable of performing the above-mentioned magnetic separation.

In low magnetic force separation, it is preferable to use a magnetic force with a surface magnetic flux density of 350 to 550 gauss. This is to separate ferromagnetic iron as magnetic material. In high magnetic force separation, it is preferable to use a magnetic force with a surface magnetic flux density of 5000 gauss or more. This is to effectively recover cobalt, nickel, and lithium, some of which are attached to the aluminum foil in the large-diameter sieved material, as magnetic material. This also allows aluminum foil to which cobalt, etc., is not attached to be effectively removed. The above surface magnetic flux density refers to the magnetic flux density at the surface of the position where the medium-diameter or large-diameter sieved material is subjected to magnetic force in the magnetic separator. For example, in a pulley-type magnetic separator in which a belt conveyor is wrapped around a magnet pulley, it is the surface magnetic flux density on the magnet pulley when the large-diameter sieved material on the belt conveyor passes through the magnet pulley.

The magnetic material obtained by magnetic separation (high magnetic separation) is crushed in the re-crushing process to produce re-crushed material. Here, the magnetic material is crushed into relatively small pieces, and the metals derived from the positive electrode that are mainly attached to the aluminum foil are rubbed off, while the aluminum foil that does not have the metals derived from the positive electrode attached is not crushed as much as possible.

The re-crushed material is then sieved again to separate it into oversized material containing aluminum and undersized material containing cobalt, nickel, lithium, etc. The undersized material obtained by re-sieving has a sufficiently reduced amount of aluminum and can be subjected to the acid leaching process as battery powder C. On the other hand, the oversized material obtained by re-sieving can be subjected to the lithium leaching process and alkaline leaching process as an Al-containing intermediate. The residue obtained after the lithium leaching process and alkaline leaching process for this oversized material or magnetized material becomes battery powder D, which is then subjected to the acid leaching process.

As shown by the dashed arrow in Figure 2, it is also possible to not separate the medium-sized and large-sized sieved materials, but to subject them to the above-mentioned magnetic separation (low magnetic separation) together and then proceed to the subsequent steps.

(Lithium leaching process)
In the lithium leaching step, the Al-containing intermediate obtained in the pretreatment step is brought into contact with a liquid by, for example, immersing and stirring the liquid, and lithium in the Al-containing intermediate is selectively leached into the liquid. The liquid used has a pH of 7 to 13 after contact with the Al-containing intermediate.

By carrying out the lithium leaching process prior to the subsequent alkaline leaching process, the lithium in the Al-containing intermediate can be leached into liquid and recovered. As a result, it is possible to suppress the loss of lithium that would otherwise occur when lithium is leached together with aluminum in the alkaline leaching process.

The liquid to be contacted with the Al-containing intermediate in the lithium leaching step is not particularly limited as long as it has a pH of 7 to 13 at the end of lithium leaching, and the pH before contacting with the Al-containing intermediate may be less than 7. The pH of the liquid before contacting with the Al-containing intermediate may be 2 to 10. The pH here means a value measured at room temperature (typically 20°C), and if the temperature of the liquid is higher, the pH is the pH when it is lowered to room temperature. The liquid is typically water, and specifically, tap water, industrial water, distilled water, purified water, ion-exchanged water, pure water, ultrapure water, etc. can be used. The liquid temperature when the Al-containing intermediate is contacted with the liquid can be 10°C to 80°C. The pulp concentration can be 25 g/L to 450 g/L. This pulp concentration means the ratio of the dry weight (g) of the Al-containing intermediate to the amount (L) of the liquid to be contacted with the Al-containing intermediate. The time for lithium leaching can be 0.1 hours to 5 hours. If the lithium leaching time is short, lithium is not sufficiently leached, and if the lithium leaching time is long, a large amount of LiAl ₂ (OH) ₇ hydrate is produced, which is difficult to leach in the subsequent alkaline leaching. For this reason, the lithium leaching time is preferably 0.5 to 3 hours.

When water, an example of the above liquid, comes into contact with an Al-containing intermediate, the pH may rise to about 11-12 due to the leaching of lithium carbonate and the like in the Al-containing intermediate. During lithium leaching, an acid such as sulfuric acid may be added as necessary to adjust the pH. The amount of acid added can be adjusted so that the pH is 7-13, preferably 7-12, at the end of lithium leaching. If the pH is less than 7, there is a risk that cobalt and the like will dissolve, and if it exceeds 12, there is a concern that aluminum and the like will dissolve.

After lithium leaching is complete, solid-liquid separation such as filtration using known devices and methods such as a filter press or thickener is performed to obtain a lithium-containing solution that mainly contains lithium ions and a residue that contains aluminum and other metals such as cobalt and nickel.

Depending on the conditions (grade of the Al-containing intermediate, pulp concentration, leaching rate, etc.), lithium may not leach into the liquid to the specified solubility. In this case, the liquid after lithium leaching (lithium-containing solution) can be used for lithium leaching again, allowing the liquid to be reused for lithium leaching. This can reduce costs and the amount of liquid.

The lithium ion concentration of the lithium-containing solution is preferably 1.0 g/L to 2.5 g/L. The lithium leaching rate in the lithium leaching process may be, for example, 40% to 60%. The lithium leaching rate can be calculated by mass from the lithium content of the Al-containing intermediate before the lithium leaching process and the lithium content of the residue obtained in the lithium leaching process.

The lithium-containing solution is used in the wet treatment, the details of which will be described later. Specifically, the lithium-containing solution can be used as at least a part of the water that is brought into contact with the battery powder in the preliminary leaching process, or as at least a part of the acid leaching solution in the acid leaching process (as at least a part of the diluent that adjusts the pH of the acid leaching solution). In particular, when the lithium-containing solution is used in the acid leaching process, the lithium-containing solution replaces the diluent, such as water that does not contain lithium, and this can increase the lithium concentration in the solution after leaching, contributing to maintaining a high lithium concentration in the solution throughout the series of processes.

The lithium-containing solution can also be used as at least a part of the cleaning solution used to clean the acid leaching residue generated in the acid leaching process or the neutralization residue generated in the neutralization process. In this case, the post-cleaning solution obtained after the cleaning can be returned to the wet treatment. When the lithium-containing solution is used as a cleaning solution for the acid leaching residue, if the leaching in the acid leaching process is only one stage, the post-cleaning solution for the acid leaching residue can be mixed with the post-leach solution and returned to the wet treatment. Alternatively, if the leaching in the acid leaching process is multiple stages, the post-cleaning solution for the acid leaching residue generated in the first leaching stage can be sent to a subsequent process such as a neutralization stage together with the post-leach solution obtained in the first leaching stage, and the post-leach solution obtained in the second leaching stage can be used in the next first leaching stage, while the post-leach solution for the acid leaching residue generated in the second leaching stage can be used in the next first leaching stage together with the post-leach solution. In this way, the loss of lithium contained in the Al-containing intermediate can be suppressed, and the lithium can be effectively utilized. Furthermore, compared to using lithium-free water as the cleaning solution, using a lithium-containing solution as the cleaning solution makes it possible to maintain a higher lithium ion concentration in the solution during wet processing after the post-cleaning solution is returned to the wet processing.

(Alkaline leaching process)
The residue obtained from the lithium leaching step is subjected to an alkali leaching step in which aluminum is separated and removed from the residue.

In the alkaline leaching process, the residue after the lithium leaching process is immersed in an alkaline solution and stirred, etc., to bring it into contact with the alkaline solution, and the aluminum in the residue is leached into the alkaline solution. By leaching lithium in the lithium leaching process described above, the residue after the lithium leaching process has a relatively low lithium content. Therefore, even if a small amount of lithium is leached from the residue along with the aluminum in the alkaline leaching process, the amount of lithium leached is reduced. This makes it possible to suppress lithium loss.

The alkaline solution used in the alkaline leaching step can have a pH of 13.0 or more and an OH ^- concentration of 8 mol/L or less before contact with the residue. The pH of the alkaline solution after contact with the residue is preferably maintained at 12.0 or more, and further preferably at 13.0 or more. The OH ^- concentration of the alkaline solution after contact with the residue may be 8 mol/L or less. By maintaining the pH within the above range when leaching aluminum, the solubility of aluminum is high, leaching is performed in a pH range in which aluminum is sufficiently dissolved, and filterability is prevented from being deteriorated due to high alkali. From this viewpoint, the OH ^- concentration of the alkaline solution after contact with the residue is preferably 5 mol/L or less. By lowering the OH ^- concentration to a certain extent, components such as sodium derived from the alkaline solution can be easily removed during washing after solid-liquid separation, and there is also an advantage that an increase in the amount of acid consumed in the acid leaching step due to the components when the acid leaching step is performed thereafter is suppressed. As the alkaline solution, for example, a sodium hydroxide solution, a potassium hydroxide solution, etc. can be used. The above pH refers to a value measured at room temperature (typically 20° C.), and when the temperature of the alkaline solution is higher, the pH is the value measured when the temperature is lowered to room temperature.

The temperature of the alkaline solution used to leach aluminum from the residue in the alkaline leaching process is preferably maintained within the range of 10°C to 80°C, and more preferably within the range of 10°C to 50°C. If the liquid temperature is too high, there is a concern that the reactivity will be high, causing sudden generation of hydrogen or a sudden rise in the liquid temperature that will become uncontrollable. If the liquid temperature is too low, the reactivity will decrease and the alkaline separation process may take a long time. The pulp concentration can be, for example, 20 g/L to 500 g/L. This pulp concentration refers to the ratio of the dry weight (g) of the residue to the amount (L) of alkaline solution brought into contact with the residue. The time for leaching aluminum may be, for example, 0.5 hours to 3.0 hours.

Depending on the conditions (residue quality, pulp concentration, leaching rate, etc.), aluminum may not leach into the alkaline solution to the specified solubility. In this case, the alkaline solution after alkaline leaching (aluminum leaching solution) may be used for alkaline leaching again, allowing the alkaline solution to be used repeatedly for alkaline leaching. This can reduce costs and the amount of liquid.

After the aluminum leaching is complete, solid-liquid separation is performed to obtain an aluminum leachate containing aluminum ions and a residue containing cobalt, nickel, etc. The aluminum ion concentration in the aluminum leachate may be, for example, 2 g/L to 60 g/L, or may be 2 g/L to 40 g/L. The lithium content of the residue obtained in the alkaline leaching process is 0.5% to 8% by mass, the cobalt content is 1% to 30% by mass, the nickel content is 1% to 30% by mass, the manganese content is 1% to 30% by mass, and the aluminum content is 0.5% to 40% by mass.

In the Al-containing intermediate before the lithium leaching process, aluminum may be contained in the form of Al (metal) or a trace amount of _LiAlO2 . It is considered that _LiAlO2 is generated by the heat treatment described above. When the lithium leaching process is performed on this Al-containing intermediate, the residue after the lithium leaching process may contain Al (metal), a trace amount of _LiAlO2 , a hydrate of _LiAl2 (OH) ₇ , etc. In the alkali leaching process, the hydrate of _LiAl2 (OH) ₇ is often not dissolved. For this reason, a small amount of aluminum may remain in the residue after the alkali leaching process.

The residue obtained in the alkaline leaching process is battery powder (battery powders B and D in the example in Figure 2). This battery powder can be subjected to the acid leaching process described below.

(Pre-leaching process)
In order to extract substantially only lithium from the battery powder, the battery powder may be subjected to a preliminary leaching step before the acid leaching step described below. In the preliminary leaching step, the battery powder may be brought into contact with water. As a result, lithium in the battery powder is leached into the water. In this case, the battery powder as the preliminary leaching residue is subjected to the acid leaching step. At least a part of the water used in this step may be the lithium-containing solution described above.

However, when a preliminary leaching step is performed, the necessary equipment is required, and performing both the preliminary leaching step and the acid leaching step increases the processing time. In addition, it may be necessary to control the conditions of roasting, etc., in order to effectively leach lithium with water. Therefore, the battery powder obtained as described above may be subjected to the acid leaching step without performing the preliminary leaching step.

(Acid leaching process)
In the acid leaching step, the battery powder (or the battery powder as the preliminary leaching residue obtained in the preliminary leaching step in some cases) is leached with an acid leaching solution of sulfuric acid, nitric acid, hydrochloric acid, or other inorganic acid. This results in a metal-containing solution as a leaching solution in which the metals in the battery powder are dissolved. If necessary, solid-liquid separation can be performed after the leaching is completed to separate the acid leaching residue.

The acid leaching process may include multiple leaching stages as described below, but may also include only one leaching stage. The pH of the leaching solution after one leaching stage may be less than 2.0, typically greater than or equal to 1.0 and less than 2.0.

In the acid leaching process, a diluent such as water may be added to concentrated sulfuric acid to prepare an acid leaching solution with an adjusted pH, and battery powder may then be added to the acid leaching solution. Alternatively, in the acid leaching process, a slurry may be prepared in which battery powder is mixed with a diluent such as water, and concentrated sulfuric acid may then be added to the slurry. In the latter case, the diluent and concentrated sulfuric acid in the slurry form the acid leaching solution, and the pH of the acid leaching solution is adjusted by the amount and pH of the diluent, just as in the former case.

As mentioned above, a lithium-containing solution may be used as at least a part of the dilution solution. A lithium-containing solution may also be used as at least a part of the cleaning solution used to wash the acid leaching residue obtained after solid-liquid separation. In this case, it is preferable to return the post-washing solution obtained after the washing to the wet treatment.

In the acid leaching process, multiple leaching steps may be repeated multiple times. Each leaching step includes a first leaching step in which the battery powder is leached with an acid leaching solution, and the acid leaching residue is separated to obtain a leaching solution, and a second leaching step in which the acid leaching residue from the first leaching step is leached with an acid leaching solution to obtain a leaching solution. The leaching solution obtained in the final leaching step (the second leaching step if there are two leaching steps, the first and second leaching steps) is used by being included in the acid leaching solution of the next first leaching step. By repeating multiple leaching steps in this manner, it is possible to increase the leaching rate of the metals to be leached in the battery powder (cobalt and/or nickel, etc.), while separating most of the metals (copper, etc.) for which it is desired to suppress leaching.

As an example of repeating multiple leaching steps, in the first leaching step, leaching is stopped before copper dissolves (while the copper concentration in the acid leaching solution is below 0.01 g/L), and the acid leaching residue is extracted by solid-liquid separation. This results in a post-leaching solution that does not contain copper, but does contain cobalt and nickel. This post-leaching solution is sent as a metal-containing solution to subsequent steps such as the neutralization step described below. Meanwhile, the acid leaching residue contains copper as well as the remaining undissolved cobalt and nickel. A second leaching step is carried out to further leach cobalt and nickel from this acid leaching residue.

In the first second leaching stage, the acid leaching residue obtained in the first leaching stage is brought into contact with the acid leaching solution to leach the cobalt and nickel in the acid leaching residue. In the second leaching stage, leaching is continued even after copper has been dissolved (after the copper concentration in the acid leaching solution becomes higher than 0.01 g/L). This allows almost all of the cobalt and nickel in the acid leaching residue to be leached. After copper has been dissolved and cobalt and nickel have been sufficiently leached, the leaching is terminated and the acid leaching residue is extracted by solid-liquid separation, so that the acid leaching residue contains copper but does not substantially contain cobalt or nickel. The post-leaching solution after the acid leaching residue is extracted contains cobalt, nickel and copper. In the second leaching stage, new battery powder may be added to leach not only the metals in the acid leaching residue from the first leaching stage, but also the metals in the new battery powder. In the second leaching stage, leaching continues even after the copper has dissolved, so that the cobalt and nickel in the new battery powder can also be sufficiently leached.

　Then, in the second first leaching stage, the post-leaching solution obtained in the first second leaching stage is used as the acid leaching solution. At this time, new acid leaching solution may be added if necessary. In the second first leaching stage, the copper ions in the above-mentioned post-leaching solution are reduced by a substitution reaction with a metal less noble than copper in the new battery powder added thereto, and are precipitated as copper, which is included in the acid leaching residue. In addition, in the second first leaching stage, cobalt and nickel are dissolved from the new battery powder, but the process ends before copper is dissolved, so the acid leaching residue contains copper derived from the new battery powder as well as cobalt and nickel that remain undissolved. This acid leaching residue is extracted by solid-liquid separation and is used for leaching in the second second leaching stage. The post-leaching solution from which the acid leaching residue is extracted contains not only cobalt and nickel dissolved from the new battery powder, but also cobalt and nickel brought in from the first leaching process, and is sent to the subsequent process.

The second second leaching stage is carried out in the same manner as the first second leaching stage, and therefore a repeated explanation is omitted. Solid-liquid separation in the second leaching stage does not need to be carried out every time. If solid-liquid separation is not carried out in the second leaching stage, the post-leaching liquid containing the acid leaching residue is sent to the next leaching stage, and copper accumulates in the acid leaching residue. If solid-liquid separation is carried out in the second leaching stage at least once out of multiple leaching stages, the acid leaching residue containing copper can be separated and removed in the second leaching stage of that leaching stage. Preferably, solid-liquid separation is carried out in each second leaching stage, and the acid leaching residue containing copper is removed each time.

When multiple leaching stages are performed, the pH of the leaching solution obtained after the first leaching stage is completed and solid-liquid separation is completed may be somewhat high, at 2.5 to 3.5. In addition, the oxidation-reduction potential (ORP value, silver/silver chloride potential standard) may be 100 mV or less.

The post-leaching solution may have, for example, a nickel concentration of 10 g/L to 50 g/L, a cobalt concentration of 10 g/L to 50 g/L, a manganese concentration of 0 g/L to 50 g/L, an aluminum concentration of 1.0 g/L to 20 g/L, an iron concentration of 0.1 g/L to 5.0 g/L, and a copper concentration of 0.005 g/L to 0.2 g/L.

(neutralization process)
In the case where the metal-containing solution obtained in the acid leaching step contains aluminum, a neutralization step can be carried out after the acid leaching step. Here, the solution obtained after the acid leaching step and containing the metal ions due to the dissolution of the metal in the acid leaching step is referred to as the metal-containing solution.

In the neutralization step, the pH of the metal-containing solution is increased, and the neutralization residue is separated to obtain a neutralized liquid. The neutralization step may include a dealumination step. In the dealumination step, the pH of the metal-containing solution is increased to precipitate and remove at least a portion of the aluminum. If the metal-containing solution contains iron, the neutralization step preferably also includes a de-ironization step, which removes the iron, after the dealumination step. In the de-ironization step, an oxidizing agent is added to the dealumination solution obtained in the dealumination step, and an alkali is further added to increase the pH, thereby removing the iron. This results in a neutralized liquid such as a de-ironization liquid.

When removing aluminum in the dealumination stage, an alkaline pH adjuster may first be added to the metal-containing solution to raise the pH to, for example, a range of 2.5 to 5.0 (preferably, 3.0 to 4.5). In addition, in the dealumination stage, the oxidation-reduction potential (ORP value, silver/silver chloride potential standard) may be 50 mV to 400 mV (250 mV to 350 mV at the end). At this time, the temperature of the metal-containing solution may be 50°C to 90°C. After the aluminum has been precipitated, solid-liquid separation such as filtration is performed using known devices and methods such as a filter press or thickener, neutralization residue is removed, and a dealumination liquid is obtained.

Next, in the iron removal stage, an oxidizing agent can be added to the dealumination solution to remove iron from the dealumination solution. The addition of the oxidizing agent oxidizes the iron in the solution from divalent to trivalent, and the trivalent iron precipitates as an oxide or hydroxide at a lower pH than the divalent iron. In many cases, the iron precipitates as a solid such as iron hydroxide (Fe(OH) ₃ ). The precipitated iron can be removed as a neutralization residue by solid-liquid separation.

The oxidizing agent is not particularly limited as long as it can oxidize iron, but it is preferable to use manganese dioxide, a positive electrode active material, and/or a manganese-containing leaching residue obtained by leaching the positive electrode active material. The manganese-containing leaching residue obtained by leaching the positive electrode active material with an acid or the like may contain manganese dioxide. When the above-mentioned positive electrode active material or the like is used as the oxidizing agent, a precipitation reaction occurs in which manganese dissolved in the liquid becomes manganese dioxide, and the precipitated manganese can be removed together with the iron. In order to precipitate iron, the ORP value during oxidation is preferably 300 mV to 900 mV. After the addition of the oxidizing agent, an alkaline pH adjuster is added to adjust the pH to, for example, a range of 3.0 to 4.5, thereby precipitating the iron.

Specific examples of alkaline pH adjusters used in the dealumination and iron removal stages include lithium hydroxide, sodium hydroxide, sodium carbonate, and ammonia. As for lithium hydroxide, the lithium hydroxide solution obtained in the recovery process described below can be used, in which case lithium is circulated within the series of steps in the wet treatment.

As mentioned above, the lithium-containing solution can be used as at least a part of the cleaning solution used to clean the neutralization residue generated in the neutralization step. In this case, it is preferable to return the post-cleaning solution obtained after the cleaning to the wet treatment.

(Recovery process)
In the recovery step, manganese is extracted and removed from the metal-containing solution obtained in the neutralization step as necessary, and nickel and cobalt are then recovered.

In manganese extraction, an extractant containing a phosphate ester extractant is used, and manganese, and in some cases aluminum that was not removed in the neutralization process, are extracted and removed by solvent extraction. Examples of phosphate ester extractants include di-2-ethylhexyl phosphoric acid (abbreviation: D2EHPA or product name: DP-8R). The extractant may also be a mixture of a phosphate ester extractant and an oxime extractant.

During extraction, the equilibrium pH is preferably 2.3 to 3.5. The alkaline pH adjuster used at this time is preferably a lithium hydroxide solution obtained as described below, but separately prepared sodium hydroxide or the like may also be used. During extraction, it is desirable to perform the extraction by countercurrent multi-stage extraction in which the aqueous phase and the solvent used in each extraction flow in opposite directions. In this way, the extraction of cobalt, nickel, and lithium can be suppressed and the extraction rate of manganese can be increased. When using countercurrent multi-stage extraction, it is effective to set the equilibrium pH during the first extraction stage within the above range, for example, and to lower the equilibrium pH during each extraction stage. This results in a manganese extracted solution.

In cobalt recovery, cobalt is separated from the manganese extraction liquid obtained after manganese extraction by solvent extraction. Here, it is preferable to use a solvent containing a phosphonate ester extractant. Among them, 2-ethylhexyl phosphonate (product name: PC-88A, Ionquest 801) is particularly suitable from the viewpoint of the efficiency of separating nickel and cobalt. The extractant may be diluted with a hydrocarbon organic solvent such as an aromatic, paraffinic, or naphthenic solvent to a concentration of 10% to 30% by volume, and this may be used as the solvent.

When extracting cobalt, the equilibrium pH during extraction can be preferably set to 5.0 to 6.0. In this case, it is preferable to use a lithium hydroxide solution obtained as described below as a pH adjuster, but separately prepared sodium hydroxide or the like can also be used. This allows the cobalt in the post-manganese extraction liquid to be extracted into the solvent. When extracting cobalt, it is also preferable to perform the extraction using a countercurrent multi-stage extraction in which the aqueous phase and the solvent used in each extraction flow in opposite directions. In this way, the extraction rate of cobalt can be increased while suppressing the extraction of nickel and lithium.

During cobalt extraction, not only cobalt but also small amounts of nickel and lithium, which become impurities in the cobalt extraction process, may be extracted into the solvent. In this case, if necessary, the solvent from which cobalt was extracted may be scrubbed one or more times using a scrubbing solution such as a sulfuric acid solution with a pH of 3.5 to 5.5 to remove impurities such as nickel that may be contained in the solvent. The post-scrubbing solution may contain nickel and lithium. For this reason, it is desirable to use a part or all of the post-scrubbing solution for cobalt extraction (i.e., mix a part or all of the post-scrubbing solution with the manganese extraction solution and use this as the pre-extraction solution to extract cobalt). This allows nickel and lithium to be circulated or retained in the process without loss. However, if the solvent from which cobalt was extracted does not contain nickel or lithium, scrubbing may not be necessary.

Then, stripping is performed on the solvent that extracted the cobalt. The stripping solution used for stripping can be any inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid, but sulfuric acid is preferable when obtaining sulfate by crystallization, which will be described later. Here, the stripping is performed under pH conditions that allow as much of the cobalt as possible to be extracted from the organic phase (solvent) into the aqueous phase (stripping solution). Specifically, the pH is preferably in the range of 2.0 to 4.0. The O/A ratio and number of times can be determined as appropriate. The liquid temperature can be room temperature, but is preferably 10°C to 50°C.

The back-extraction liquid, such as the cobalt sulfate solution obtained by the back-extraction of cobalt, is crystallized. In this crystallization, the back-extraction liquid is heated, for example, to 40°C to 120°C and concentrated, so that the cobalt crystallizes and a cobalt salt, such as cobalt sulfate, is obtained. The cobalt salt thus obtained preferably has a nickel content of 5 mass ppm or less, and nickel has been sufficiently removed, so that it can be effectively used as a raw material for the manufacture of lithium-ion secondary batteries and other batteries. Here, the crystallization liquid may contain cobalt and lithium that did not crystallize. Therefore, the crystallization liquid may be mixed with the back-extraction liquid to be used for crystallization again, or may be used to adjust the cobalt concentration of the scrubbing liquid used in scrubbing after cobalt extraction, or may be used to extract cobalt. By using the crystallization liquid repeatedly in this manner within the process, it is possible to circulate or retain the cobalt and lithium within the process and concentrate them without losing them.

In recovering nickel, a carboxylic acid extractant is preferably used for the cobalt extraction liquid obtained after cobalt extraction to separate the nickel. Examples of carboxylic acid extractants include neodecanoic acid and naphthenic acid, with neodecanoic acid being preferred due to its ability to extract nickel. The extractant may be diluted with a hydrocarbon organic solvent such as an aromatic, paraffinic, or naphthenic solvent to a concentration of 10% to 30% by volume, and this may be used as the solvent.

When extracting nickel, the equilibrium pH is preferably 6.0 to 8.0. The pH adjuster used to adjust the pH at this time may be sodium hydroxide or the like, but it is preferable to use a lithium hydroxide solution obtained as described below. When extracting nickel, it is desirable to perform the extraction using a countercurrent multi-stage extraction method, as in the extraction of cobalt described above. This can suppress the extraction of lithium and increase the extraction rate of nickel.

If necessary, the solvent from which nickel has been extracted may be scrubbed one or more times using a scrubbing solution such as a sulfuric acid solution with a pH of 5.0 to 6.0 to remove impurities such as lithium and sodium that may be contained in the solvent. The post-scrubbing solution may contain lithium. For this reason, it is desirable to use a part or all of the post-scrubbing solution to extract nickel (i.e., mix a part or all of the post-scrubbing solution with the cobalt extraction solution and use this as the pre-extraction solution to extract nickel). This allows lithium to be circulated or retained in the process and concentrated without loss. However, if the solvent from which nickel has been extracted does not contain lithium, scrubbing does not need to be performed.

Then, the solvent is back-extracted using a back-extraction solution such as sulfuric acid, hydrochloric acid, or nitric acid. If crystallization is to be performed afterwards, sulfuric acid is the most preferable. The pH is preferably in the range of 1.0 to 3.0, and more preferably 1.5 to 2.5. The O/A ratio and number of times can be determined as appropriate, but the O/A ratio may be, for example, 5 to 1.

When a stripping liquid such as a nickel sulfate solution is obtained by stripping, it can be electrolyzed and dissolved as necessary, then heated to 40°C to 120°C to crystallize the nickel as a nickel salt such as nickel sulfate. This results in a nickel salt. The crystallization liquid may contain nickel and lithium that did not crystallize. Therefore, the crystallization liquid can be mixed back into the stripping liquid to be used for crystallization and used again for crystallization, or it can be used to adjust the nickel concentration of the scrubbing liquid used in scrubbing after nickel extraction, or it is desirable to use it for nickel extraction. By using it repeatedly within the process in this way, nickel and lithium can be concentrated by circulating or retaining them within the process without loss.

The nickel extraction solution (lithium sulfate solution, etc.) after nickel has been extracted can be used as at least a part of the dilution solution used to dilute concentrated sulfuric acid in the acid leaching process to adjust the pH of the acid leaching solution. This allows the lithium contained in the nickel extraction solution to be circulated within the series of steps of the acid leaching process, neutralization process, and recovery process. Preferably, after the lithium concentration in the nickel extraction solution has increased to a certain extent by circulating lithium in this way, the hydroxide described below can be carried out.

The nickel extraction solution obtained after nickel extraction is a solution such as a lithium sulfate solution that contains essentially only lithium as a result of the separation of each metal. If necessary, trace amounts of cations such as nickel and magnesium can be removed using ion exchange resins or chelating resins, and then hydroxide can be performed to obtain a lithium hydroxide solution. Hydroxidation can be performed, for example, using the carbonation and formation method in which calcium hydroxide is used after lithium carbonate is produced, the formation method using barium hydroxide, and a method using electrodialysis, as described below.

In the case of the carbonation and chemical conversion method, first, a lithium carbonate solution is obtained by adding carbonate or blowing carbon dioxide gas into the nickel extraction liquid. Then, in the so-called chemical conversion method, calcium hydroxide is added to the lithium carbonate solution to generate a lithium _hydroxide solution under the reaction formula _Li2CO3 +Ca(OH) ₂ →2LiOH+ _CaCO3 . Calcium that may remain in the liquid can be removed by using a cation exchange resin, a chelating resin, or the like.

When barium hydroxide is used, it is added to the solution after nickel extraction, and a _lithium hydroxide solution can be obtained based on the reaction _Li2SO4 + Ba(OH) ₂ → 2LiOH + _BaSO4 . Note that barium that may dissolve in the solution at this time can be separated and removed using a cation exchange resin, a chelating resin, or the like.

In electrodialysis, in a bipolar membrane electrodialysis device, the nickel extraction solution is placed in the desalting chamber between the anion exchange membrane and the cation exchange membrane, while pure water is placed in the acid chamber between the bipolar membrane and the anion exchange membrane and the alkaline chamber between the cation exchange membrane and the bipolar membrane, and a voltage is applied between the electrodes. This causes the lithium in the metal-containing solution in the desalting chamber to move to the alkaline chamber, where the bipolar membrane breaks down the pure water into hydroxide ions, producing a lithium hydroxide solution. The anions of inorganic acids such as sulfuric acid in the metal-containing solution in the desalting chamber pass through the anion exchange membrane and move to the acid chamber.

At least a portion of the lithium hydroxide solution obtained as described above can be effectively used as an alkaline pH adjuster for use in at least one step selected from the group consisting of the neutralization step and the recovery step (at least one of the extractions when multiple extractions are performed in the recovery step).

As mentioned above, if the lithium hydroxide solution is returned to the neutralization process or manganese extraction as a pH adjuster, the lithium concentration in the solution may gradually increase due to the lithium in the newly added battery powder. Depending on the lithium concentration, the lithium hydroxide solution obtained by hydroxide oxidation may be subjected to a crystallization procedure such as heating and concentration or reduced pressure distillation to precipitate and recover lithium hydroxide.

Next, the metal recovery method described above was experimentally implemented and its effectiveness was confirmed, which will be explained below. However, the explanation here is merely for illustrative purposes and is not intended to be limiting.

Example 1
As shown in FIG. 2, the lithium ion battery waste was subjected to heat treatment, crushing and sieving, and the large diameter sieved matter obtained by the sieving was further subjected to magnetic separation, re-crushing and re-sieving, and the Al-containing intermediate with the quality (mass%) shown in Table 1 was obtained as the sieved matter of the re-sieving. The small diameter sieved matter obtained by the sieving was designated as battery powder A. The medium diameter sieved matter obtained by the sieving was subjected to eddy current separation, and the magnetic material separated by the eddy current separation was designated as battery powder B. The under-sieved matter obtained by the above re-sieving was designated as battery powder C. The quality of the combination of battery powder A, battery powder B and battery powder C was as shown in Table 2. The distribution rate is the ratio of each metal distributed to the battery powder when the quality of each metal contained in the wound body and electrolyte of the lithium ion battery waste before treatment is 100% by mass.

Table 2 shows that battery powders A to C have a relatively high distribution rate of cobalt and nickel, but as shown in Table 1, the Al-containing intermediate also contained a certain amount of cobalt, etc. In order to remove aluminum from the Al-containing intermediate and recover cobalt, etc., the following process was carried out.

The Al-containing intermediate was subjected to lithium leaching for 5 hours with a pulp concentration of 100 g/L and a liquid temperature of room temperature (20°C). Distilled water with a pH of 5.8 was used for lithium leaching. Figure 4 shows the change in the leaching rate of aluminum and lithium over time. In lithium leaching, a high lithium leaching rate is desirable from the viewpoint of suppressing lithium loss during the subsequent alkaline leaching, and a low aluminum leaching rate is desirable from the viewpoint of recovering high-purity lithium. The pH at the end of leaching was 12.7. All of the cobalt and nickel were transferred to the residue and were not leached.

From Figure 4, we can see that lithium leaching was almost complete within one hour, and the leaching rate remained constant thereafter. Also, a small amount of aluminum was leached.

Then, the residue after lithium leaching was immersed in an alkaline solution to perform alkali leaching of aluminum. Here, a sodium hydroxide aqueous solution with a concentration of 50 g/L was used as the alkaline solution, the pulp concentration was 50 g/L, the liquid temperature was room temperature (20°C), and the leaching time was 5 hours. As a result, the graph shown in Figure 5 was obtained. Note that the leaching rate was calculated by assuming that the mass of each metal in the Al-containing intermediate before lithium leaching was 100%. Figure 5 also shows the change in pH over time. In alkaline leaching, a higher aluminum leaching rate is desirable because it reduces the amount of aluminum distributed in the alkaline leaching residue (battery powder D) (and the amount of aluminum carried over to the subsequent acid leaching).

From Figure 5, it can be seen that the aluminum leaching rate was 49% after 1 hour, and gradually decreased after 2 hours. The lithium leaching rate was suppressed to about 8%. Table 3 shows the purity and distribution rate of the combined battery powders A to C shown in Table 2 and the residue (battery powder D) obtained after 1 hour of alkaline leaching. When this is further added to the lithium in the lithium-containing solution obtained by lithium leaching, the purity and distribution rate of each recovered metal are as shown in Table 4.

As shown in Table 4, it was possible to remove a certain amount of aluminum while recovering most of the cobalt, nickel, and lithium.

Example 2
Alkaline leaching of aluminum was carried out in the same manner as in Example 1 using the same residue after lithium leaching as in Example 1, except that the liquid temperature was 50° C. As a result, one hour after the start of alkaline leaching, the leaching rate of aluminum was 62%, and the leaching rate of lithium was about 13%.

In alkaline leaching, at both liquid temperatures of 20°C in Example 1 and 50°C in Example 2, all of the cobalt and nickel transferred to the residue and were not leached.

Table 5 shows the purity and distribution rate of the sum of battery powders A to C shown in Table 2 and the residue (battery powder D) obtained after one hour of alkaline leaching, and Table 6 shows the purity and distribution rate of the sum of these and the lithium in the lithium-containing solution obtained by lithium leaching.

As shown in Table 6, it was possible to recover most of the cobalt, nickel and lithium while removing some of the aluminum.

Example 3
The same procedure as in Example 1 was followed except that the lithium leaching was completed after 1 hour, followed by the alkaline leaching. The pH at the end of the lithium leaching was 12.8.

In the alkaline leaching, after 1 hour had passed since the start of leaching, the leaching rate of aluminum was 55% and the leaching rate of lithium was 9%. The leaching rate of aluminum increased by about 5% compared to Example 1. This is considered to be due to the fact that the lithium leaching time was shortened to the minimum time required for lithium leaching, thereby suppressing the formation of _LiAl2 (OH) ₇ hydrate, which is difficult to leach by alkaline leaching, during lithium leaching.

Table 7 shows the purity and distribution rate of the sum of battery powders A to C shown in Table 2 and the residue (battery powder D) obtained after one hour of alkaline leaching, and Table 8 shows the purity and distribution rate of the sum of these and the lithium in the lithium-containing solution obtained by lithium leaching.

Example 4
The same as in Example 2, except that the lithium leaching was completed in 1 hour, followed by the alkaline leaching, and the alkaline leaching was completed in 3 hours. The pH at the end of the lithium leaching was 12.2.

In alkaline leaching, one hour after the start of leaching, the leaching rate of aluminum was 89%, and the leaching rate of lithium was 16%. When the lithium leaching time was shortened from 5 hours to 1 hour, the leaching rates of both aluminum and lithium in alkaline leaching were higher than in Example 2.

Table 9 shows the purity and distribution rate of the sum of battery powders A to C shown in Table 2 and the residue (battery powder D) obtained after one hour of alkaline leaching, and Table 10 shows the purity and distribution rate of the sum of these and the lithium in the lithium-containing solution obtained by lithium leaching.

(Comparative Example 1)
Except for not performing lithium leaching, the procedure was the same as in Example 2. Table 11 shows the grades and distribution ratios of the battery powders A to C shown in Table 2 plus the residue (battery powder D) obtained after one hour of alkaline leaching.

Table 11 shows that the distribution rate of lithium is low. This is due to the loss of lithium caused by alkaline leaching.

From the above, it was found that the metal recovery method described above can effectively remove aluminum while suppressing lithium loss.

Claims (15)

A method for recovering metals from lithium ion battery waste, comprising the steps of:
a pretreatment step of subjecting the lithium ion battery waste to a pretreatment step including a heat treatment to obtain an Al-containing intermediate containing aluminum and lithium;
a lithium leaching step of contacting the Al-containing intermediate with a liquid to leach lithium in the Al-containing intermediate into the liquid, adjusting the pH of the liquid at the end of the lithium leaching to 7 to 13, and obtaining a residue and a lithium-containing solution;
an alkaline leaching step of contacting the residue from the lithium leaching step with an alkaline solution to leach aluminum in the residue into the alkaline solution, thereby obtaining a residue and an aluminum-containing solution;
a wet treatment for leaching metals in the battery powder containing the residue from the alkaline leaching step, and separating metal ions from a metal-containing solution in which the metals are dissolved;
The method for recovering metals, wherein the lithium-containing solution obtained in the lithium leaching step is used in the wet treatment. The metal recovery method according to claim 1, wherein the wet treatment includes an acid leaching step in which the metal in the battery powder is leached with an acidic leaching solution, and the lithium-containing solution is used in the acid leaching step. The metal recovery method according to claim 2, in which the lithium-containing solution is used as at least a part of the cleaning solution used to clean the acid leaching residue generated in the acid leaching step, and the cleaning solution is returned to the wet treatment. The metal recovery method according to any one of claims 1 to 3, wherein the wet treatment includes a neutralization step of increasing the pH of the metal-containing solution, and the lithium-containing solution is used in the neutralization step. The metal recovery method according to claim 4, in which the lithium-containing solution is used as at least a part of the cleaning solution used to wash the neutralization residue generated in the neutralization step, and the cleaning solution is returned to the wet treatment. the wet treatment includes a pre-leaching step of leaching lithium in the battery powder before the acid leaching step;
4. The method for recovering metals according to claim 2 or 3, wherein the lithium-containing solution is used in the pre-leaching step. 4. The metal recovery method according to claim 1, wherein, in the alkaline leaching step, the pH of the alkaline solution before contacting the residue is set to 13.0 or more, the OH ^- concentration of the alkaline solution after contacting the residue is set to 8 mol/L or less, and the liquid temperature of the alkaline solution is set to 10° C. to 80° C. The metal recovery method according to any one of claims 1 to 3, wherein the lithium ion battery waste is heated to a temperature of 100°C or higher during the heat treatment in the pretreatment step. The pretreatment step includes crushing the lithium ion battery waste to obtain crushed material, and sieving the crushed material to obtain an undersize material and an oversize material,
The metal recovery method according to any one of claims 1 to 3, wherein the Al-containing intermediate comprises the sieve residue. The metal recovery method according to claim 9, wherein the battery powder further includes the undersize material. The metal recovery method according to claim 9, wherein the crushed material is separated by the sieving into at least small-diameter sieved matter having a relatively small particle size, large-diameter sieved matter having a relatively large particle size, and medium-diameter sieved matter having a particle size intermediate between the small-diameter sieved matter and the large-diameter sieved matter. The metal recovery method according to claim 11, wherein the Al-containing intermediate material includes the medium-sized sieved material or a magnetic material obtained by performing eddy current sorting on the medium-sized sieved material. The pretreatment step includes magnetic separation for extracting magnetic materials from the large diameter sieved material, re-crushing for crushing the magnetic materials to obtain re-crushed materials, and re-sieving for sieving the re-crushed materials to obtain undersize materials and oversize materials,
The metal recovery method according to claim 12, wherein the Al-containing intermediate comprises the sieve residue. The metal recovery method according to any one of claims 1 to 3, wherein the lithium leaching time in the lithium leaching step is 0.5 to 3 hours. The metal recovery method according to any one of claims 1 to 3, wherein the lithium ion battery waste contains cobalt and/or nickel, and the metal-containing solution contains cobalt ions and/or nickel ions.

Images