WO2025187459A1 - Impurity removal method and metal recovery method - Google Patents

Abstract

Provided is a method for removing impurities including aluminum from a metal-containing solution which is obtained from lithium battery waste and which contains aluminum ions, iron ions, cobalt ions, and/or nickel ions, said method comprising a dealumination step for removing aluminum by raising the pH of the metal-containing solution under the presence of phosphate ions and precipitating aluminum, wherein the iron ions in the metal-containing solution provided for the dealumination step include divalent iron ions.

Description

Method for removing impurities and method for recovering metals

This specification describes a method for removing impurities and a method for recovering metals.

In recent years, recovery of valuable metals from waste batteries, such as lithium-ion batteries discarded due to product lifespan, manufacturing defects, or other reasons, has been widely considered from the perspective of effective resource utilization.

For example, to recover metals from lithium-ion battery waste, the battery powder obtained through heat treatment and other processes is brought into contact with an acidic leachate, and the metals in the battery powder are leached into the acidic leachate. This produces a metal-containing solution in which nickel, cobalt, manganese, aluminum, iron, etc. are dissolved.

Next, the metals are separated from the metal-containing solution. Specifically, as described in Patent Documents 1 to 3, for example, impurities such as aluminum and iron, and manganese are separated sequentially or simultaneously from the metals dissolved in the metal-containing solution by neutralization or solvent extraction. Nickel and cobalt are then separated by solvent extraction and concentrated for extraction.

In this regard, Patent Document 4 describes "a method for removing aluminum and iron in _the recycling of rechargeable batteries, the method comprising: a) preparing a leachate from black mass; b) adding phosphoric acid ( _H3PO4 ) to the leachate from step a); c) adjusting the pH to form iron phosphate ( _FePO4 ) and aluminum phosphate ( _AlPO4 ); d) precipitating and removing the formed _FePO4 and _AlPO4 ; and e) forming a filtrate for recovering cathode metals." Patent Document 4 also states that "the first precipitation at a low pH has the advantage of minimizing co-precipitation of lithium and NMC metals. When a second precipitation step is performed, fewer solids are present, which is advantageous because it counteracts the tendency for co-precipitation at higher pH."

JP 2010-180439 A US Patent Application Publication No. 2011/0135547 JP 2014-162982 A Special Publication No. 2022-528969

In order to precipitate and remove aluminum from a metal-containing solution by neutralization, it is thought to be advantageous to carry out the neutralization in a situation where phosphate ions are present in the metal-containing solution, for example by adding a phosphate ion source.

In this case, it has been newly discovered that when iron ions are present in addition to aluminum ions in the metal-containing solution, under certain conditions, more phosphate ions than are required for aluminum precipitation may be required. Because phosphate ion sources are relatively expensive, using large amounts of phosphate ion sources increases the cost of treating lithium-ion battery waste.

This specification discloses a method for removing impurities and a method for recovering metals that can reduce the amount of phosphate ion source used and contribute to lower processing costs.

One impurity removal method disclosed in this specification is a method for removing impurities containing aluminum from a metal-containing solution obtained from lithium-ion battery waste and containing aluminum ions, iron ions, cobalt ions, and/or nickel ions, and includes a dealumination step in which the pH of the metal-containing solution is increased in the presence of phosphate ions to precipitate and remove aluminum, and the iron ions in the metal-containing solution subjected to the dealumination step include divalent iron ions.

Another impurity removal method disclosed in this specification is a method for removing impurities containing aluminum from a metal-containing solution obtained from lithium-ion battery waste and containing aluminum ions, iron ions, cobalt ions, and/or nickel ions, and includes a dealumination step in which the pH of the metal-containing solution is increased in the presence of phosphate ions to precipitate and remove aluminum, and the oxidation-reduction potential (based on silver/silver chloride potential) of the metal-containing solution is set to less than 500 mV when the dealumination step is initiated.

The metal recovery method disclosed in this specification involves recovering metals including cobalt and/or nickel from a metal-containing solution from which impurities have been removed using the impurity removal method described above.

The above impurity removal method reduces the amount of phosphate ion source used, contributing to lower processing costs.

1 is a flow chart showing an example of a metal recovery method including an impurity removal method according to an embodiment of the present invention. FIG. 1 is a flow chart showing an example of a pretreatment process for obtaining battery powder from lithium ion battery waste. FIG. 2 is a flow diagram showing details of the acid leaching step included in the metal recovery method of FIG. 1. 1 is a graph showing the change in iron ion concentration with respect to the change in pH during dealumination in Test Example 1. 1 is a graph showing the change in aluminum ion concentration with respect to the change in pH during dealumination in Test Example 1. 1 is a graph showing the change in phosphorus concentration with respect to the change in pH during dealumination in Test Example 1. 1 is a graph showing the change in oxidation-reduction potential (based on silver/silver chloride potential) with respect to the change in pH during dealumination in Test Example 1. 1 is a graph showing the change in iron ion concentration with respect to the change in pH during dealumination in Test Example 2. 1 is a graph showing the change in aluminum ion concentration with respect to the change in pH during dealumination in Test Example 2. 1 is a graph showing the change in phosphorus concentration with respect to the change in pH during dealumination in Test Example 2.

Hereinafter, an embodiment of the present invention will be described in detail.
In one embodiment, the impurity removal method targets a metal-containing solution obtained from lithium-ion battery waste, the metal-containing solution containing aluminum ions, iron ions, and cobalt ions and/or nickel ions.

This impurity removal method includes a dealumination step in which, in order to remove at least aluminum from the metal-containing solution, the pH of the metal-containing solution is increased in the presence of phosphate ions, thereby precipitating and removing aluminum. Here, the iron ions in the metal-containing solution subjected to the dealumination step include divalent iron ions, and/or the oxidation-reduction potential (based on silver/silver chloride potential) of the metal-containing solution is set to less than 500 mV when the dealumination step is initiated.

It has been discovered that when the metal-containing solution used in the dealumination step contains trivalent iron ions, a large amount of phosphate ions in the metal-containing solution are consumed in the reaction with the trivalent iron ions, resulting in a larger amount of phosphate ion source than is required for the reaction with the aluminum ions. This is particularly evident when the iron ions are oxidized from divalent to trivalent when an oxidizing agent is added in the dealumination step. Based on this discovery, the metal-containing solution used in the aluminum step is assumed to contain divalent iron ions. Additionally or alternatively, the oxidation-reduction potential (based on silver/silver chloride potential) of the metal-containing solution is set to less than 500 mV when the dealumination step is initiated. If the oxidation-reduction potential (based on silver/silver chloride potential) of the metal-containing solution is less than 500 mV, it is believed that at least a portion, typically almost the majority, of the iron ions in the metal-containing solution have become divalent iron ions. This allows more phosphate ions to be used in the reaction with the aluminum ions, thereby reducing the amount of phosphate ion source used. As a result, the cost of chemicals for the phosphate ion source is reduced, thereby reducing the cost of treating lithium-ion battery waste.

The impurity removal method of this embodiment may be implemented, for example, in a metal recovery method having the steps shown in Figure 1. In Figure 1, battery powder from lithium-ion battery waste is subjected to an acid leaching step, a dealumination step, a de-ironization step, a manganese extraction step, a cobalt extraction step, a nickel extraction step, a hydroxide step, and a crystallization step, in this order. Battery powder can be obtained by subjecting lithium-ion battery waste to a pretreatment step, as shown in Figure 2. Here, the explanation will be given according to Figures 1 and 2, but Figures 1 and 2 are merely examples and the method is not limited to these specific flows.

(Lithium-ion battery waste)
The target lithium-ion battery waste is lithium-ion secondary batteries that can be used in mobile phones and various other electronic devices, etc., that have been discarded due to the end of the battery product's life, manufacturing defects, or other reasons. Recovering valuable metals from such lithium-ion battery waste is preferable from the perspective of effective resource utilization.

Lithium-ion battery waste has an aluminum-containing casing as the exterior that encases the battery. For example, some casings are made of aluminum alone, while others contain aluminum and iron, aluminum laminate, etc. Lithium-ion battery waste may also contain, within the casing, a positive electrode active material made of a single metal oxide containing lithium and one or more selected from the group consisting of nickel, cobalt, and manganese, or a composite metal oxide containing two or more selected metals. It may also contain aluminum foil (positive electrode substrate) to which the positive electrode active material is coated and fixed with, for example, polyvinylidene fluoride (PVDF) or other organic binders. Lithium-ion battery waste may also contain copper, iron, etc. Furthermore, the casing of lithium-ion battery waste typically contains an electrolyte solution, in which an electrolyte such as lithium hexafluorophosphate is dissolved in an organic solvent. Examples of organic solvents that may be used include ethylene carbonate and diethyl carbonate.

(Pretreatment process)
Lithium-ion battery waste is often subjected to a pretreatment process. The pretreatment process may include at least one of roasting, crushing, and sieving. Lithium-ion battery waste is converted into battery powder through the pretreatment process. The roasting, crushing, and sieving pretreatment processes may be performed individually as needed, or may be performed in any order. Battery powder refers to a powder obtained by separating and concentrating positive electrode material components from lithium-ion battery waste through some kind of pretreatment. Battery powder may also be obtained by crushing and sieving lithium-ion battery waste with or without heat treatment, resulting in a powder with concentrated positive electrode material components.

In roasting, the lithium-ion battery waste is heated. Roasting can convert metals such as lithium and cobalt contained in the lithium-ion battery waste into a form that is easily soluble in the acid leaching solution during the acid leaching process. During roasting, it is preferable to heat the lithium-ion battery waste at a temperature ranging from 450°C to 1000°C, preferably from 600°C to 800°C, for example, for 0.5 to 6 hours. Roasting can be carried out either in air or in an inert atmosphere such as nitrogen. It can also be carried out in both air and an inert atmosphere, either in that order or in the reverse order. The roasting furnace can be either a batch or continuous furnace; for example, a stationary furnace is used for the batch method, and a rotary kiln is used for the continuous method. Various other furnaces can also be used.

During roasting, at least a portion of the electrolyte is removed from the lithium-ion battery waste, for example, by evaporating the electrolyte solution. In many cases, when lithium-ion battery waste is heated during roasting, the components of the internal electrolyte evaporate sequentially, starting with those with low boiling points. Furthermore, when the lithium-ion battery waste reaches even higher temperatures, resins such as organic binders decompose or vaporize. Even if some of the electrolyte solution and organic binder are removed in this way, certain components contained in the electrolyte solution and organic binder, such as fluorine, remain and may be contained in the battery powder obtained after the pretreatment process. When roasting is performed, the electrolyte is removed and rendered harmless, and the organic binder is decomposed, facilitating the separation of the aluminum foil and the positive electrode active material during the crushing and sieving processes described below. Although the composition of the positive electrode active material changes due to roasting, the term "positive electrode active material" will be used here even if the material has undergone roasting.

After roasting, the lithium-ion battery waste can be crushed to remove the positive electrode active material and other components from the casing. Crushing involves destroying the casing of the lithium-ion battery waste and selectively separating the positive electrode active material from the aluminum foil to which it is applied.

A variety of known devices or equipment can be used for shredding, but it is particularly preferable to use an impact crusher, which can shred the lithium-ion battery waste by applying impact while cutting it. Examples of impact crushers include sample mills, hammer mills, pin mills, wing mills, tornado mills, and hammer crushers. A screen can be installed at the outlet of the crusher, so that the lithium-ion battery waste is discharged from the crusher through the screen once it has been crushed to a size that can pass through the screen.

After the lithium-ion battery waste is crushed, it is sieved using a sieve with appropriate mesh size. This leaves aluminum and copper on the sieve, while the battery powder below the sieve has some of the aluminum and copper removed.

If the battery powder obtained in the pretreatment step contains nickel, the nickel content is, for example, 1% by mass to 30% by mass, typically 5% by mass to 20% by mass. Furthermore, if cobalt is contained, the cobalt content in the battery powder is, for example, 1% by mass to 30% by mass, typically 5% by mass to 20% by mass. Furthermore, the battery powder may contain, for example, 2% by mass to 8% by mass of lithium, 1% by mass to 30% by mass of manganese, 1% by mass to 10% by mass of aluminum, 1% by mass to 5% by mass of iron, and 1% by mass to 10% by mass of copper.

In order to extract essentially only lithium from the battery powder, the battery powder may be brought into contact with water before the acid leaching process described below, allowing the lithium in the battery powder to leach into the water. In this case, the battery powder as the water leaching residue is subjected to the acid leaching process. When water leaching is performed, at least a portion of the electrolyte and other electrolytes in the lithium-ion battery waste are removed, for example by leaching into the water.

However, when water leaching is performed, the necessary equipment is required, and performing both water leaching and acid leaching in the acid leaching step increases the processing time. In addition, it may be necessary to control roasting conditions, etc., to effectively leach lithium with water. Even with such control, the leaching rate of lithium with water may not be significantly increased. Therefore, the battery powder obtained as described above may be subjected to the acid leaching step without water leaching. If water leaching is not performed, it becomes easier to maintain a high lithium ion concentration in the solution during the wet processing that follows the acid leaching step.

In addition to the roasting and water leaching methods described above, the lithium ion battery waste may also be washed with a cleaning solution such as water at any time during the pretreatment process to remove electrolytes from the lithium ion battery waste in the pretreatment process.

(Acid leaching process)
In the acid leaching process, metals in the battery powder, including at least aluminum, iron, cobalt, and/or nickel, are leached with an acidic leaching solution containing sulfuric acid, nitric acid, hydrochloric acid, or other inorganic or mineral acids. This results in a post-leaching solution (metal-containing solution) containing at least aluminum ions, iron ions, and cobalt ions and/or nickel ions. Here, the term "metal-containing solution" refers to a solution containing metal ions obtained by dissolving the metals in the acid leaching process and sent to the next process, the dealumination process. The term "metal-containing solution" may also refer to a solution undergoing processes subsequent to the dealumination process.

Regarding pH, the acidic leachate during leaching is preferably kept between -0.5 and 3.0, and the pH of the post-leaching solution after leaching may be between 0.5 and 2.0. During leaching, for example, the acidic leachate may be stirred at 100 to 400 rpm using a stirrer as needed, and the solution temperature may be set to 50 to 80°C, or even 65 to 70°C.

In the acid leaching step, the acid leachate may contain phosphate ions. If the acid leachate contains phosphate ions, aluminum will precipitate as a compound such as aluminum orthophosphate (AlPO ₄ ), which can be removed. The phosphate ions not consumed in the acid leaching step can be used to precipitate and remove aluminum during neutralization in the next step, the dealumination step.

The phosphate ion source may be contained in the battery powder, but if this is not sufficient, a phosphate ion source can be added to the acidic leachate separately from the battery powder. The phosphate ion source may be added to the acidic leachate together with the battery powder, or may be added to the acidic leachate before or after contacting the battery powder with the acidic leachate. The phosphate ion source may be added after the start of leaching. Furthermore, for example, when battery powder is mixed with water such as distilled water to form a slurry and then an acid such as sulfuric acid is added to the slurry to form the acidic leachate, the phosphate ion source may be added to the slurry before the acid is added, or the phosphate ion source may be added to the slurry together with the acid. If a phosphate ion source is contained in lithium-ion battery waste and the battery powder obtained by performing a pretreatment process on it, the acidic leachate will contain phosphate ions when the battery powder comes into contact with the acidic leachate.

Various phosphate ion sources can be added to the acidic leaching solution as long as they generate phosphate ions (PO ₄ ^3- ) upon contact with the acidic leaching solution.Specific examples include phosphoric acid (H ₃ PO ₄ ), calcium phosphate (Ca ₃ (PO ₄ ) ₂ , etc.), calcium hydrogen phosphate (CaHPO ₄ ), trisodium phosphate (Na ₃ PO ₄ ), disodium hydrogen phosphate (Na ₂ HPO ₄ ), sodium dihydrogen phosphate (NaH ₂ PO ₄ ), and lithium phosphate (Li ₃ PO ₄ ).

The amount of phosphoric acid to be added to the acid leaching solution can be determined appropriately, taking into account the aluminum content of the battery powder and other conditions. Specifically, the battery powder to be added to the acid leaching process can be subjected to a component analysis in advance to determine the aluminum content of the battery powder, and the amount of phosphoric acid can be determined based on this. For example, the molar ratio of phosphorus in the phosphoric acid to aluminum (P/Al molar ratio) is preferably 0.5 or greater, and more preferably 1.0 or greater but less than 1.5.

The acid leaching process may involve multiple leaching stages, as described below, or only one leaching stage. Alternatively, as shown in Figure 3, multiple leaching stages may be repeated multiple times. Each of the multiple leaching stages includes a first leaching stage in which the metals in the battery powder are leached with an acid leaching solution, the leaching is terminated before the copper is eluted, and the leaching residue is separated to obtain a leaching solution, and a second leaching stage in which the leaching residue from the first leaching stage is leached with an acid leaching solution, the leaching is terminated after the copper is eluted, and a leaching solution is obtained. The leaching solution obtained in the first leaching stage is used as a metal-containing solution and sent to the dealumination process, described below. Meanwhile, the leaching solution obtained in the final leaching stage of the multiple leaching stages (the second leaching stage if there are two leaching stages, the first and second leaching stages) is used by being included in the acid leaching solution for the next first leaching stage.

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 (such as cobalt and/or nickel), while separating much of the copper, the leaching of which should be suppressed, as leaching residue. More detailed information is provided below. Here, as an example, we will explain a case where the battery powder contains cobalt, nickel, and copper, but it may not contain either cobalt or nickel, or may further contain other metals.

As an example of repeating multiple leaching stages, in the first leaching stage, leaching is stopped before copper dissolves (for example, while the copper ion concentration in the acidic leaching solution is 0.01 g/L or less), and the leaching residue is removed by solid-liquid separation. This results in a leaching solution that has a lower copper ion concentration than the leaching solution obtained in the second leaching stage described below, and contains cobalt ions and nickel ions. This leaching solution is sent to the subsequent process as a metal-containing solution. Meanwhile, the leaching residue contains copper as well as the remaining undissolved cobalt and nickel. A second leaching stage is carried out to further leach cobalt and nickel from this leaching residue.

In the first second leaching stage, the leaching residue obtained in the first leaching stage is contacted with an acidic leaching solution to leach the cobalt and nickel in the leaching residue. In the second leaching stage, leaching is continued even after the copper has dissolved (for example, after the copper ion concentration in the acidic leaching solution becomes higher than 0.01 g/L). This allows almost all of the cobalt and nickel in the leaching residue to be leached. After the copper has dissolved and the cobalt and nickel have been sufficiently leached, the leaching is terminated and the leaching residue is removed by solid-liquid separation. The leaching residue will contain reduced cobalt and nickel and will contain copper. The post-leaching solution after the leaching residue has been removed will contain cobalt ions, nickel ions, and copper ions. In the second leaching stage, new battery powder may be added to leach not only the metals in the 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, allowing the cobalt and nickel in the new battery powder to be sufficiently leached as well.

Next, in the second first leaching stage, the post-leaching solution obtained in the first second leaching stage is used as the acidic leaching solution. At this time, new acidic leaching solution can be added if necessary. In the second first leaching stage, the copper ions in the post-leaching solution are reduced in a substitution reaction by metals less noble than copper contained in the new battery powder added thereto, resulting in the precipitation of copper, which is then contained in the leaching residue. Furthermore, in the second first leaching stage, cobalt and nickel are dissolved from the new battery powder, but the process ends before the copper is dissolved. Therefore, the leaching residue contains copper from the new battery powder as well as the cobalt and nickel that remain undissolved. This leaching residue is extracted by solid-liquid separation and used for leaching in the second second leaching stage. The post-leaching solution from which the leaching residue has been extracted contains not only the cobalt and nickel ions dissolved from the new battery powder, but also the cobalt and nickel ions carried over from the first leaching stage, 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, so a repeated explanation will be omitted. Solid-liquid separation does not need to be carried out every time the second leaching stage is carried out. If solid-liquid separation is not carried out in the second leaching stage, the post-leaching liquid containing the leaching residue will be sent to the next first leaching stage, and copper will accumulate in the leaching residue. If solid-liquid separation is carried out in the second leaching stage at least once out of multiple leaching stages, the leaching residue containing copper can be separated and removed in that second leaching stage. Preferably, solid-liquid separation is carried out in each second leaching stage, and the leaching residue containing copper is removed each time.

Here, "before copper is leached" in the first leaching stage refers to a state in which the copper ion concentration in the acidic leaching solution is lower than that of the post-leaching solution obtained in the second leaching stage of that cycle. For example, a state in which the copper ion concentration in the acidic leaching solution is 0.01 g/L or less may be considered "before copper is leached." However, this copper ion concentration does not include the copper ion concentration in the post-leaching solution obtained in the previous second leaching stage and used as the acidic leaching solution in the current first leaching stage. When the post-leaching solution obtained in the previous second leaching stage is used as the acidic leaching solution in the first leaching stage, the period in which the relatively high copper ion concentration before leaching tends to decrease due to copper precipitation through the substitution reaction can be considered "before copper is leached" after the copper ion concentration has temporarily dropped to 0.01 g/L or less and remains at 0.01 g/L or less. In this case, leaching may be terminated while the copper ion concentration is 0.01 g/L or less (before the copper ion concentration exceeds 0.01 g/L).

Furthermore, "after copper leaching" in the second leaching stage means a state in which the copper ion concentration in the acidic leaching solution is higher than that of the post-leaching solution obtained in the first leaching stage in that cycle. Therefore, in each cycle, the copper ion concentration in the post-leaching solution obtained in the second leaching stage will be higher than that of the post-leaching solution obtained in the first leaching stage. For example, the state may be considered "after copper leaching" when the copper ion concentration in the acidic leaching solution is higher than 0.01 g/L. In the second leaching stage, leaching may be terminated, for example, after the copper ion concentration in the acidic leaching solution becomes higher than 0.01 g/L.

In the first and second leaching stages, the oxidation-reduction potential (based on silver/silver chloride potential) of the acidic leaching solution may be well below 0 mV before leaching, and may gradually increase as leaching progresses. Hereinafter, "oxidation-reduction potential (based on silver/silver chloride potential)" will be referred to simply as "oxidation-reduction potential." This oxidation-reduction potential is also sometimes referred to as ORP.

In the first leaching stage, leaching is preferably terminated before the redox potential of the acidic leaching solution reaches 0 mV or higher, and more preferably before it reaches higher than -300 mV. If the redox potential becomes too high, the copper ion concentration may increase to some extent, and there is a risk that copper ions will be contained in the solution after leaching.

On the other hand, in the second leaching stage, it is preferable to terminate leaching after the redox potential of the acidic leachate reaches 0 mV or higher. This allows most of the cobalt and nickel to be leached out, minimizing loss of cobalt and nickel. However, in the second leaching stage, it is preferable to terminate leaching before the redox potential of the acidic leachate reaches 60 mV or higher, in order to prevent excessive copper from being leached out.

Furthermore, in the first and second leaching stages, once metal leaching has progressed to a certain extent, the rate of increase in the redox potential of the acidic leachate tends to accelerate. In the first leaching stage, in order to suppress copper leaching, it is preferable to terminate the leaching before the hourly increase in the redox potential of the acidic leachate reaches 233 mV or more. On the other hand, in the second leaching stage, from the perspective of leaching as much cobalt and nickel as possible, it is preferable to terminate the leaching after the hourly increase in the redox potential of the acidic leachate reaches 233 mV or more. Here, the hourly increase in redox potential refers to the value obtained by subtracting the redox potential value one hour prior to a given time from the redox potential value at that time.

In the first and second leaching stages, leaching can be considered complete when, for example, stirring by the agitator that was being used during leaching is stopped and the next step, such as solid-liquid separation or the addition of new battery powder, is started. Solid-liquid separation to remove the leaching residue from the post-leaching solution can be performed using known devices and methods, such as a filter press or thickener.

The multiple leaching stages may include not only a first leaching stage and a second leaching stage, but also three or more leaching stages. For example, the first leaching stage and/or the second leaching stage may be divided into multiple stages. In this case, each of the multiple divided first leaching stages is terminated while the copper ion concentration in the acidic leaching solution is lower than the copper ion concentration in the post-leaching solution obtained in the second leaching stage. For example, each of the multiple first leaching stages may be terminated while the copper ion concentration in the acidic leaching solution is 0.01 g/L or less. Furthermore, each of the multiple divided second leaching stages is terminated after the copper ion concentration in the acidic leaching solution is higher than the copper ion concentration in the post-leaching solution obtained in the first leaching stage. For example, each of the multiple second leaching stages may be terminated after the copper ion concentration in the acidic leaching solution is higher than the copper ion concentration in the post-leaching solution obtained in the first leaching stage.

When repeating the first and second leaching stages described above multiple times, if cobalt or nickel migrates to the leaching residue of the second leaching stage, it will lead to a loss of cobalt or nickel, so it is desirable to minimize this as much as possible. Specifically, if the battery powder contains cobalt, when the sum or total of the cobalt content of the battery powder subjected to the first leaching stage in a given cycle and the cobalt ion content of the acidic leaching solution used in the first leaching stage in that cycle is taken as 100%, it is preferable that the sum of the cobalt ion content of the post-leaching solution obtained in the first leaching stage and the post-leaching solution obtained in the second leaching stage be 95% or more in each cycle. Furthermore, when the battery powder contains nickel, the sum of the nickel ion content in the post-leaching solution obtained in the first leaching step and the nickel ion content in the post-leaching solution obtained in the second leaching step is preferably 95% or more in each leaching step, where the sum or total of the nickel content of the battery powder subjected to the first leaching step in a given cycle and the nickel ion content of the acid leaching solution used in that cycle is 100% by mass. Here, in the first leaching step, the cobalt ion content and nickel ion content of the acid leaching solution used in the first leaching step are both zero. In the second and subsequent leaching steps, the cobalt ion content and nickel ion content of the acid leaching solution used in the first leaching step refer to the cobalt ion content and nickel ion content of the post-leaching solution obtained in the previous second leaching step and used as the acid leaching solution in the first leaching step.

When a phosphate ion source is added in an acid leaching process that includes multiple leaching stages, the timing of addition is not particularly important as long as it is before the end of the leaching stage (after the end of leaching and before solid-liquid separation, if solid-liquid separation is performed), but it is preferable to add it in the first leaching stage. In this case, the first leaching stage is likely to reduce the aluminum ion concentration in the post-leaching solution sent to the dealumination process as a metal-containing solution, and it is possible to increase the phosphate ion concentration in the acid leaching solution. If a phosphate ion source is added to the acid leaching solution in the second leaching stage to precipitate aluminum, the phosphate ions will be consumed in the second leaching stage. In this case, if the post-leaching solution obtained in the second leaching stage is used as the acid leaching solution for the next first leaching stage, there is a risk that a sufficient amount of phosphate ions will not be obtained to precipitate aluminum in the new battery powder. Note that even if a phosphate ion source is added in the first leaching stage, aluminum may still precipitate in the second leaching stage. If the phosphorus content of the battery powder is insufficient during each repeated leaching stage, the necessary amount of phosphoric acid can be added separately.

The metal-containing solution obtained in the acid leaching process may have, for example, a cobalt ion concentration of 10 g/L to 50 g/L, a nickel ion concentration of 10 g/L to 50 g/L, a manganese ion concentration of 0 g/L to 50 g/L, an aluminum ion concentration of 1.0 g/L to 20 g/L, an iron ion concentration of 0.1 g/L to 5.0 g/L, and a copper ion concentration of 0.005 g/L to 0.2 g/L. The metal-containing solution does not need to contain at least one of nickel ions and cobalt ions, as long as it contains the other.

(Dealuminization process)
The dealumination step is carried out to remove aluminum ions from the metal-containing solution obtained in the acid leaching step. Specifically, the pH of the metal-containing solution is increased to precipitate at least a portion of the aluminum ions. Thereafter, solid-liquid separation such as filtration is carried out using known devices and methods such as a filter press or a thickener to remove neutralization residue and obtain a dealumination solution.

In the dealumination process, the pH of the metal-containing solution is increased in the presence of phosphate ions. This makes it easier for the aluminum ions in the metal-containing solution to precipitate due to the phosphate ions, allowing for effective removal of aluminum. At this time, the iron ions in the metal-containing solution subjected to the dealumination process should contain divalent iron ions. This reduces the consumption of phosphate ions due to reaction with trivalent iron ions, allowing aluminum to precipitate with fewer phosphate ions.

If the metal-containing solution already contains the required amount of phosphate ions, for example because the battery powder contains phosphorus or because a phosphate ion source was added during the acid leaching process, it may not be necessary to add a phosphate ion source. Alternatively, if the metal-containing solution does not contain phosphate ions or if the phosphate ions in the metal-containing solution are insufficient, a phosphate ion source may be added to the metal-containing solution before, during, and/or after the pH of the metal-containing solution is increased to a predetermined value.

The form of the phosphate ion source added to the metal-containing solution is not particularly limited, and examples thereof include _phosphoric acid ( _H3PO4 ), calcium phosphate ( _Ca3 ( _PO4 ) ₂ , etc.), calcium hydrogen phosphate ( _CaHPO4 ), trisodium phosphate ( _Na3PO4 ), disodium hydrogen phosphate ( _Na2HPO4 ), _{sodium dihydrogen} phosphate ( _NaH2PO4 ) _, lithium phosphate ( _Li3PO4 ), etc. When the metal-containing solution contains phosphate ions _, the neutralization residue generated in the dealumination step may contain compounds such as aluminum orthophosphate ( _AlPO4 ).

It is believed that aluminum ions and phosphate ions in the metal-containing solution react according to the formula: Al ³⁺ +PO ₄ ^3- →AlPO _4. When the dealumination step is initiated, the content of phosphate ions in the metal-containing solution is preferably 0.1 to 1.5 molar equivalents of the amount required for the reaction with the aluminum ions in the metal-containing solution. 0.5 to 1.5 molar equivalents is more preferable. If the amount of phosphate ions is too small, aluminum may not be sufficiently precipitated, while if the amount is too large, a large amount of phosphate ion source may be required, resulting in a certain increase in chemical costs.

In the dealumination process, the pH of the metal-containing solution can be increased, for example, to within the range of 3.0 to 4.0 by adding a pH adjuster. Because the metal-containing solution contains phosphate ions, aluminum is effectively precipitated even at such a relatively low pH, which prevents coprecipitation of cobalt and nickel that would occur if the pH were higher. In other words, if the metal-containing solution does not contain phosphate ions, the pH of the metal-containing solution must be increased to a relatively high value to precipitate aluminum, which would also cause cobalt and nickel to precipitate, resulting in their loss. To further prevent coprecipitation of cobalt and nickel, the pH of the metal-containing solution may be increased to within the range of 3.0 or more and 3.5 or less (or less than 3.5). On the other hand, to more effectively precipitate aluminum, the pH of the metal-containing solution may be increased to within the range of 3.5 or more (or more than 3.5) and 4.0 or less.

In the dealumination process, it is preferable not to add an oxidizing agent in order to suppress oxidation of iron ions and convert as many of them as possible to divalent iron ions. Oxidizing agents can act to oxidize iron from divalent to trivalent, and examples include hydrogen peroxide, manganese dioxide, positive electrode active materials for lithium-ion batteries, and manganese-containing leaching residue obtained by leaching positive electrode active materials.

Furthermore, in the dealumination step, it is preferable to set the oxidation-reduction potential (based on silver/silver chloride potential) of the metal-containing solution to less than 500 mV at the start of the step. It is estimated that if the oxidation-reduction potential (based on silver/silver chloride potential) at the start is relatively low, the metal-containing solution will contain a large amount of iron ions in a divalent state. The temperature of the metal-containing solution in the dealumination step can be set to 50°C to 90°C.

When the dealumination process is complete, the phosphorus concentration of the metal-containing solution is preferably in the range of 0.4 g/L to 1.0 g/L. After the phosphate ions have been sufficiently consumed in the dealumination process and the phosphorus concentration has decreased, the iron removal process, described next, can be carried out.

(Deiron removal process)
After the dealumination step, a deironization step can be carried out. In the deironization step, an oxidizing agent is added to the metal-containing solution as the dealumination solution to precipitate iron in the metal-containing solution. The precipitated iron can be removed as neutralization residue by solid-liquid separation.

To precipitate iron, the oxidation-reduction potential (based on the silver/silver chloride potential) during oxidation is preferably 300 mV to 900 mV. After the addition of the oxidizing agent, an acid such as sulfuric acid, hydrochloric acid, or nitric acid can be added to lower the pH to, for example, less than 3. Thereafter, if necessary, an alkaline pH adjuster can be added to raise the pH to, for example, within the range of 3.0 to 4.0, thereby precipitating iron. The addition of the oxidizing agent oxidizes the iron ions in the solution from divalent to trivalent. Since trivalent iron ions are more likely to precipitate as oxides or hydroxides, typically as solids such as iron hydroxide (Fe(OH) ₃ ), at lower pHs than divalent iron ions, it may not be necessary to raise the pH.

The oxidizing agent used in the iron removal process is not particularly limited as long as it can oxidize iron, but it is preferably manganese dioxide, a positive electrode active material, and/or a manganese-containing leaching residue obtained by leaching a positive electrode active material. Manganese-containing leaching residue obtained by leaching a 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 along with the iron. Alternatively, the above-mentioned oxidizing agent may be supplied by adding hydrogen peroxide or by blowing in a gas such as ozone or air containing oxygen.

Specific examples of alkaline pH adjusters used in the dealumination and iron removal processes include lithium hydroxide, sodium hydroxide, sodium carbonate, and ammonia. The lithium hydroxide solution obtained in the hydroxide process described below can be used, in which case lithium ions circulate throughout the series of wet processing steps.

(Manganese extraction process)
The metal-containing solution obtained after the iron removal step as a post-iron removal solution can be subjected to solvent extraction to extract and remove manganese ions, and in some cases, residual aluminum ions as well. In this case, the residual manganese ions and aluminum ions are extracted to obtain a post-manganese extraction solution from which they have been removed.

In the manganese extraction process, it is preferable to use an extractant containing a phosphate ester extractant. Examples of phosphate ester extractants include di-2-ethylhexyl phosphoric acid (abbreviated as D2EHPA or product name: DP-8R). The extractant may also be a mixture of a phosphate ester extractant and an oxime extractant. In this case, the oxime extractant is preferably an aldoxime or one whose main component is aldoxime. Specific examples include 2-hydroxy-5-nonylacetophenone oxime (product name: LIX84), 5-dodecylsalicyaldoxime (product name: LIX860), a mixture of LIX84 and LIX860 (product name: LIX984), and 5-nonylsalicylaldoxime (product name: ACORGAM5640).

During extraction, the equilibrium pH is preferably set to 2.3 to 3.5, more preferably 2.5 to 3.0. The alkaline or other pH adjuster used here is preferably the lithium hydroxide solution obtained in the hydroxide process described below, but separately prepared sodium hydroxide or the like may also be used. When the lithium hydroxide solution obtained in the hydroxide process is used as the pH adjuster, it is possible to prevent the sodium from remaining in the lithium-containing solution after the nickel extraction process described below, as well as to prevent the sodium from being mixed in as an impurity into the lithium hydroxide solution produced from that lithium-containing solution, as occurs when sodium hydroxide is used as the pH adjuster.

During extraction, it is desirable to use countercurrent multi-stage extraction, in which the aqueous phase and solvent used in each extraction flow in opposite directions. This prevents cobalt ions, nickel ions, and lithium ions from being extracted, and increases the extraction rate of manganese ions. When using countercurrent multi-stage extraction, it is effective to set the equilibrium pH of the de-ironized liquid to a value within the above range during the first extraction stage, and then increase the equilibrium pH during each subsequent extraction stage.

Because the solvent used to extract manganese ions may contain cobalt ions, nickel ions, and lithium ions, it can be subjected to stripping after scrubbing. For example, the scrubbing solution can be a sulfuric acid solution with a pH of 2.0 to 3.0, and the stripping solution can be a sulfuric acid solution with a pH of 0.0 to 1.0. It is desirable to use the scrubbing solution or stripping solution for manganese extraction (for example, mixing the scrubbing solution with a metal-containing solution and using the resulting solution as a pre-extraction solution to extract manganese ions, using the stripping solution to scrub the solvent used to extract manganese ions, or using the scavenging solution as a stripping solution for the solvent used to extract manganese ions). This allows the cobalt ions, nickel ions, and lithium ions to be circulated or retained within the process without loss. However, if the solvent used to extract manganese ions does not contain cobalt ions, nickel ions, or lithium ions, scrubbing or stripping is not necessary.

(Cobalt extraction process)
Next, a cobalt extraction step can be carried out. In the cobalt extraction step, cobalt ions are separated by solvent extraction from the manganese extraction solution obtained after the manganese extraction step.

In the cobalt extraction process, it is preferable to use a solvent containing a phosphonate ester extractant. Among these, 2-ethylhexyl 2-ethylhexyl phosphonate (trade names: PC-88A, Ionquest 801) is particularly suitable from the standpoint of nickel and cobalt separation efficiency. 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 ions, the equilibrium pH during extraction can be preferably set to 5.0 to 6.0, more preferably 5.0 to 5.5. In this case, it is preferable to use the lithium hydroxide solution obtained in the hydroxide process described below as the pH adjuster, but separately prepared sodium hydroxide or the like can also be used. If the pH is below 5.0, there is a risk that the cobalt ions will not be sufficiently extracted into the solvent. This allows the cobalt ions in the post-manganese extraction solution to be extracted into the solvent.

Furthermore, when extracting cobalt ions, it is desirable to use a countercurrent multi-stage extraction method in which the aqueous phase and solvent used in each extraction flow in opposite directions. This method can increase the extraction rate of cobalt ions while suppressing the extraction of nickel ions and lithium ions.

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

The solvent from which the cobalt ions have been extracted is then subjected to stripping. 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, as described below. Here, the stripping is carried out under pH conditions that will extract as much of the cobalt ions as possible 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, and even more preferably in the range of 2.5 to 3.5. 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 stripped solution, such as the cobalt sulfate solution obtained by stripping cobalt ions, can be crystallized. In crystallization, the stripped solution is concentrated by heating, for example, to 40°C to 120°C, thereby crystallizing the cobalt ions as a cobalt salt. The cobalt salt produced in this manner preferably has a nickel content of 5 mass ppm or less, and since nickel has been sufficiently removed, it can be effectively used as a raw material for the manufacture of lithium-ion secondary batteries and other batteries. The crystallized solution may contain cobalt ions and lithium ions that did not crystallize. Therefore, it is desirable to mix the crystallized solution with the stripped solution before crystallization and use it again for crystallization, to adjust the cobalt ion concentration of the scrubbing solution used as a solvent after cobalt ion extraction, or to use it for cobalt extraction. By repeatedly using the crystallized solution within the process in this way, the cobalt ions and lithium ions can be circulated or retained within the process and concentrated without loss.

(Nickel extraction process)
Thereafter, the cobalt-extracted solution after the cobalt ions have been extracted can be subjected to a nickel extraction step.

In the nickel extraction process, a carboxylic acid extractant is preferably used to separate nickel ions from the post-cobalt extraction solution. Examples of carboxylic acid extractants include neodecanoic acid and naphthenic acid, with neodecanoic acid being preferred due to its ability to extract nickel ions. 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 ions, the equilibrium pH is preferably set to 6.0 to 8.0, more preferably 6.8 to 7.2. The pH adjuster used to adjust the pH at this time can be sodium hydroxide or the like, but it is preferable to use the lithium hydroxide solution obtained in the hydroxide oxidation process described below. When extracting nickel ions, it is desirable to use a countercurrent multi-stage extraction method, similar to the extraction of cobalt ions described above. This prevents lithium ions from being extracted, and increases the extraction rate of nickel ions.

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

The solvent from which the nickel ions have been extracted is then 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 preferred. The pH is preferably in the range of 1.0 to 3.0, 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 should be 5 to 1, more preferably 4 to 2.

When a stripping solution such as a nickel sulfate solution is obtained by stripping, it can be electrolyzed and dissolved as needed, then heated to 40-120°C to crystallize the nickel ions as nickel salts such as nickel sulfate. This yields nickel salts. The crystallized solution may contain nickel ions and lithium ions that did not crystallize. Therefore, it is desirable to mix the crystallized solution with the stripping solution before crystallization and use it for further crystallization, to use it to adjust the nickel ion concentration in the scrubbing solution used as a solvent after nickel ion extraction, or to use it for nickel extraction. By using it repeatedly within the process in this way, the nickel ions and lithium ions can be circulated or retained within the process and concentrated without loss.

As mentioned above, at least a portion of the lithium-containing solution after the nickel ions have been extracted can be mixed with the acid leaching solution in the acid leaching process and used. This allows the lithium ions contained in the lithium-containing solution to be circulated within a series of processes including the acid leaching process, dealumination process, iron removal process, and various extraction processes. Preferably, after the lithium ion concentration in the lithium-containing solution has increased to a certain extent by circulating the lithium ions in this way, the hydroxide process described below is carried out.

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

For example, a lithium carbonate solution is first obtained by adding a carbonate or blowing carbon dioxide gas into a lithium sulfate solution. Then, as a so-called chemical conversion method, calcium hydroxide is added to the lithium carbonate solution to produce a lithium _hydroxide solution according to the reaction formula _Li2CO3 + Ca(OH) ₂ → 2LiOH + _CaCO3 . Calcium ions that may remain in the solution can be removed using a cation exchange resin, a chelating resin, or the like.

Alternatively, a lithium hydroxide solution can be obtained by adding barium hydroxide to a _lithium sulfate solution and carrying out 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.

Alternatively, when using the so-called electrolysis method, a lithium sulfate solution can be supplied to the anode side and electrolysis can be performed in an electrolytic cell equipped with a cation exchange membrane that separates the anode side and the cathode side, thereby producing a lithium hydroxide solution on the cathode side.

The lithium hydroxide solution obtained in this way can be effectively used as a pH adjuster (neutralizer) in the dealumination and iron removal processes, as well as an alkaline pH adjuster in the manganese extraction process, cobalt extraction process, and nickel extraction process.

In the electrolysis method, which is one of the methods mentioned above, electrodialysis can be performed by supplying a lithium sulfate solution to the deionization compartment between the anion exchange membrane and the cation exchange membrane in a bipolar membrane electrodialysis device. In this case, a lithium hydroxide solution is obtained in the alkaline compartment between the cation exchange membrane and the bipolar membrane, while an acidic solution such as a sulfuric acid solution can be obtained in the acid compartment between the bipolar membrane and the anion exchange membrane. Such an acidic solution can be included in the post-separation liquid as mentioned above and mixed with the acidic leachate in the acid leaching process.

It should be noted that the lithium-containing solution may contain trace amounts of cations, such as nickel ions and magnesium ions, that were not completely separated during the nickel extraction process. Nickel ions and magnesium ions are cations, just like lithium ions, and behave similarly to lithium ions during the electrodialysis described above, making them difficult to separate from lithium ions. Furthermore, if electrodialysis is performed on a lithium-containing solution containing nickel ions and magnesium ions, nickel and magnesium hydroxides may be generated in the resulting lithium hydroxide solution, raising concerns that process problems could prevent the electrodialysis from continuing. For this reason, in such cases, it is desirable to perform washing to remove cations, such as nickel ions and magnesium ions, from the lithium-containing solution prior to electrodialysis. For example, an ion exchange resin or chelating resin can be used for this washing.

(Crystallization process)
After the hydroxide step, a crystallization step may be performed to precipitate lithium hydroxide from the lithium hydroxide solution. For example, when a series of steps including the acid leaching step to the nickel extraction step is repeated, the lithium ion concentration in a solution such as a lithium sulfate solution may gradually increase as new lithium ion battery waste is added to the series of steps. After the lithium ion concentration in the solution has increased to a certain level, the crystallization step may be performed.

In the crystallization process, crystallization procedures such as heating and concentration or vacuum distillation can be performed to precipitate lithium hydroxide. In the case of heating and concentration, the higher the temperature during crystallization, the faster the process progresses, so this is preferable. However, after crystallization, it is preferable to dry the crystallized material at a temperature below 60°C, at which point water of crystallization does not escape. If water of crystallization escapes, the resulting material becomes anhydrous lithium hydroxide, which is deliquescent and difficult to handle. The lithium hydroxide obtained in the crystallization process can be subjected to grinding or other processes to adjust the required physical properties.

Next, we conducted tests to confirm the effectiveness of the above-mentioned impurity removal method, which are described below. However, this description is for illustrative purposes only and is not intended to be limiting.

(Test Example 1)
Metals in battery powder obtained by pretreatment such as roasting in an air atmosphere for lithium-ion battery waste were leached by acid leaching including multiple leaching stages as shown in Figure 3. In this acid leaching, the pH in the first leaching stage was set to 2.5, and the pH in the second leaching stage was set to 1.5, and calcium phosphate ( _Ca3 ( _PO4 ) ₂ ) was added in the first leaching stage so that the P/Al molar ratio was 0.75. As a result, a metal-containing solution with the metal concentrations, pH, and oxidation-reduction potential (based on silver/silver chloride potential, ORP) shown in Table 1 was obtained as the leaching filtrate from the first leaching stage. The metal concentration was measured using an ICP optical emission spectrometer SPS3300 manufactured by SII NanoTechnology Inc., the pH was measured using a multi-purpose water quality meter MX-43X and a composite electrode GST-5841C manufactured by DKK-TOA Corporation, and the redox potential was measured using a multi-purpose water quality meter MX-43X and a composite electrode PST-5721C manufactured by DKK-TOA Corporation. Similar analysis or measurement devices were used in Test Example 2 described below.

Thereafter, 600 mL of the metal-containing solution was neutralized with a 4N LiOH aqueous solution to precipitate aluminum for dealumination. In Comparative Example 1, 1 mL of 30% _hydrogen peroxide ( _H2O2 ) water was added as an oxidizing agent, while in Example 1, no hydrogen _peroxide ( _H2O2 ) was added. As a result, graphs showing the changes in iron ion concentration, aluminum ion concentration, phosphorus concentration, and oxidation-reduction potential (based on silver/silver chloride potential, ORP) with changes in pH were obtained, as shown in Figures 4 to 7.

Figures 4 to 6 show that in Example 1, where hydrogen peroxide was not added, the iron ion concentration was higher, the aluminum ion concentration was generally lower, and the phosphorus concentration was higher compared to Comparative Example 1, where hydrogen peroxide was added. This is thought to be because, by not adding hydrogen peroxide in Example 1, iron ions were not oxidized from divalent to trivalent, making it difficult for iron to precipitate, and because the consumption of phosphate ions due to reaction with iron was suppressed, more phosphate ions reacted with aluminum ions, resulting in the precipitation of aluminum.

Furthermore, as shown in Figure 7, in Example 1, in which hydrogen peroxide was not added, the oxidation-reduction potential (based on silver/silver chloride potential) was lower in the early and middle stages, including the start of dealumination, than in Comparative Example 1, in which hydrogen peroxide was added, but became higher at the end. This is presumably because in Example 1, the oxidation-reduction potential (based on silver/silver chloride potential) was low in the early and middle stages due to the presence of divalent iron ions, a reducing substance, in the solution, but as the concentration of divalent iron ions decreased, the oxidation-reduction potential (based on silver/silver chloride potential) shifted to the side with higher oxidizing power.

(Test Example 2)
A lithium-ion battery waste different from that in Test Example 1 was subjected to substantially the same pretreatment as in Test Example 1 to obtain a battery powder. This battery powder was subjected to acid leaching under substantially the same conditions except that calcium phosphate was not added. As a result, a metal-containing solution having the metal concentrations, pH, and oxidation-reduction potential (based on silver/silver chloride potential, ORP) shown in Table 2 was obtained as the leaching filtrate from the first leaching stage.

Thereafter, the pH of the metal-containing solution was increased to 3.0, phosphoric acid ( _H3PO4 ) was added in proportion to the aluminum ion concentration, and the pH was further increased to 3.5, phosphoric acid ( _H3PO4 ) was added in proportion to the aluminum ion concentration. Dealuminization was carried out in a manner substantially similar to that of Test Example ₁ , except that: in Comparative Example 2, 1 mL of 30% aqueous hydrogen peroxide ( _H2O2 ) was added as an oxidizing agent; in Example ₂ , no hydrogen peroxide ( _H2O2 ) was added. The total amount of 85% phosphoric acid ( _{H3PO4 )} added was 5.717 mL in Comparative Example 2 _and 5.600 mL in Example 2. As a result, graphs showing the changes in iron ion concentration, aluminum ion concentration, and phosphorus concentration with changes _in pH were obtained, as shown in Figures 8 to 10.

Figure 8 shows that Example 2, in which hydrogen peroxide was not added, had a higher iron ion concentration than Comparative Example 2, in which hydrogen peroxide was added. This is thought to be because, since hydrogen peroxide was not added in Example 2, the iron ions were not oxidized from divalent to trivalent, making it difficult for the iron to precipitate.

9 and 10 show that, near pH 3 when phosphoric acid was added, Example 2 ( _{no H2O2} added) had a lower aluminum ion concentration and a higher phosphorus concentration than Comparative Example 2 ( _{with H2O2} added). From this, it is believed that, as in Example 1, the absence of hydrogen peroxide in Example 2 prevented iron ions from being oxidized from divalent to trivalent, making iron less likely to precipitate. Furthermore, the consumption of phosphate ions due to reaction with iron was suppressed, allowing more phosphate ions to react with aluminum ions. Furthermore, since more phosphoric acid was added near pH 3.5 and the total amount added was greater in Comparative Example 2 than in Example 2, it is presumed that the final Al and P concentrations in Example 2 and Comparative Example 2 were similar.

The above suggests that the impurity removal method described above may be able to reduce the amount of phosphate ion source used, thereby contributing to lower processing costs.

Claims (12)

A method for removing impurities containing aluminum from a metal-containing solution obtained from lithium ion battery waste and containing aluminum ions, iron ions, and cobalt and/or nickel ions, comprising the steps of:
a dealumination step of increasing the pH of the metal-containing solution in the presence of phosphate ions to precipitate and remove aluminum;
The impurity removal method, wherein the iron ions in the metal-containing solution to be subjected to the dealumination step include divalent iron ions. A method for removing impurities containing aluminum from a metal-containing solution obtained from lithium ion battery waste and containing aluminum ions, iron ions, and cobalt and/or nickel ions, comprising the steps of:
a dealumination step of increasing the pH of the metal-containing solution in the presence of phosphate ions to precipitate and remove aluminum;
The method for removing impurities, wherein the oxidation-reduction potential (based on silver/silver chloride potential) of the metal-containing solution is set to less than 500 mV when the dealumination step is started. The impurity removal method according to claim 1 or 2, wherein the pH of the metal-containing solution is increased to 3.0 to 4.0 in the dealumination step. The impurity removal method according to claim 1 or 2, wherein, when the dealumination step is initiated, the content of phosphate ions in the metal-containing solution is 0.1 to 1.5 molar equivalents of the amount required to react with aluminum ions in the metal-containing solution. The impurity removal method described in claim 1, wherein the oxidation-reduction potential (based on silver/silver chloride potential) of the metal-containing solution is set to less than 500 mV when the dealumination step is initiated. The impurity removal method according to claim 1 or 2, wherein no oxidizing agent is added in the dealumination step. The impurity removal method described in claim 1 or 2, wherein the phosphorus concentration of the metal-containing solution upon completion of the dealumination step is within the range of 0.4 g/L to 1.0 g/L. The impurity removal method according to claim 1 or 2, further comprising a de-ironization step in which, after the dealumination step, an oxidizing agent is added to the metal-containing solution to precipitate and remove iron from the metal-containing solution. The impurity removal method according to claim 8, wherein the pH of the metal-containing solution is increased during the iron removal process. The impurity removal method described in claim 8, wherein the pH of the metal-containing solution is set within the range of 3.0 to 4.0 during the iron removal process. The impurity removal method according to claim 1 or 2, further comprising an acid leaching step, prior to the dealumination step, in which battery powder from lithium-ion battery waste containing aluminum, iron, cobalt, and/or nickel is leached in an acidic leaching solution to obtain the metal-containing solution. A metal recovery method for recovering metals containing cobalt and/or nickel from a metal-containing solution from which impurities have been removed using the impurity removal method described in claim 1 or 2.