JP7815938B2 - Method for leaching electrode materials, method for separating cobalt and nickel - Google Patents

Description

The present invention relates to a method for leaching electrode materials for lithium-ion secondary batteries, and a method for separating cobalt and nickel using the same.

Lithium-ion secondary batteries are used as power sources in a wide range of fields, from small devices such as various electronic devices to large devices such as electric vehicles. When these lithium-ion secondary batteries are discarded, there is a need to recover and reuse the useful metals.

A lithium ion secondary battery is formed by stacking negative and positive electrode materials in layers, separated by a separator such as porous polypropylene, and sealing them in a case made of aluminum or stainless steel together with an electrolyte such as lithium hexafluorophosphate (LiPF ₆ ) and an electrolytic solution.

The negative electrode material for lithium-ion secondary batteries is formed by applying a negative electrode active material such as graphite mixed with a binder to a negative electrode current collector made of copper foil or the like. The positive electrode material is formed by applying a positive electrode active material such as lithium manganese oxide, lithium cobalt oxide, or lithium nickel oxide mixed with a binder to a positive electrode current collector made of aluminum foil or the like.

As such, the positive electrode active material of lithium-ion secondary batteries contains large amounts of cobalt and nickel, but the positive electrode active material that is crushed and separated in advance during the recycling process also contains manganese, copper, aluminum, lithium, and other elements in addition to cobalt and nickel. Therefore, in order to separate and recover cobalt and nickel from lithium-ion secondary batteries with a high yield, it is necessary to accurately remove metals other than these.

Conventionally, one method for separating and recovering cobalt and nickel contained in lithium-ion secondary batteries is disclosed in Patent Document 1, which discloses a method for recovering cobalt and nickel in which electrode material for lithium-ion secondary batteries is acid-leached using sulfuric acid to produce a leachate, sulfide is added to this leachate to precipitate copper sulfide, and then aluminum hydroxide and manganese oxide are precipitated, and the cobalt and nickel are recovered from the resulting solution.

JP 2015-183292 A

However, in the recovery method disclosed in Patent Document 1, in the leaching step in which the electrode material is leached with acid to produce a leachate, the electrode material is primarily composed of hydrophobic carbon derived from the negative electrode material, making it difficult to mix with sulfuric acid and water. Furthermore, gas generated during the acid leaching causes some of the electrode material to become hard foam and float up, slowing the reaction between the electrode material and sulfuric acid and lengthening the reaction time. As a result, there are issues with the leaching step being lengthened and the need to add an excess amount of sulfuric acid, more than the reaction equivalent, to drive the reaction.

This invention was made in consideration of the above-mentioned circumstances, and aims to provide a method for leaching electrode materials contained in lithium-ion secondary batteries that can be acid-leached efficiently in a short time without using an excessive amount of acid, and a method for separating cobalt and nickel that includes this leaching method.

In light of the above background, the inventors discovered that by using a two-step process in the leaching process for acid-leaching electrode material, in which the electrode material is first mixed with a small amount of sulfuric acid to form a leaching paste, which is a paste-like leachate, and then diluting this leach paste with water, it is possible to acid-leach electrode material efficiently in a short time without using excess sulfuric acid.

That is, in order to solve the above-mentioned problems, the electrode material leaching method of the present invention is a method for acid-leaching an electrode material for a lithium-ion secondary battery, and includes a leaching process in which the electrode material for a lithium-ion secondary battery is reacted with sulfuric acid to obtain a leachate in which metals contained in the electrode material are leached, and the leaching process is characterized by including a kneading process in which the sulfuric acid and the electrode material are kneaded to form a leached paste, and a dilution process in which the leached paste is diluted with water.

According to the present invention, the leaching process involves two steps: a kneading step and a dilution step. This makes it possible to acid-leach the electrode material efficiently in a short time without using an excessive amount of acid.

In addition, in the present invention, the kneading process may be performed so that, when the mass (g) of the electrode material is EA, the volume (mL) of the sulfuric acid is SV, and the concentration (mol/L) of the sulfuric acid is SC, the following relationships are satisfied: 1≦(SV/EA)≦2 and 5.5EA≦(SC×SV)≦10.3EA.

In addition, in the present invention, hydrogen peroxide may be further added during at least one of the kneading process and the dilution process.

Furthermore, in the present invention, hydrogen peroxide may be added during the dilution process after the pH is adjusted to 2.0 or less and the liquid temperature is adjusted to 50°C or higher.

Furthermore, in the present invention, sulfuric acid may be further added during the dilution process so that the pH of the diluted leachate is in the range of 2.0 or less.

In addition, in the present invention, alcohol may be further added during at least one of the kneading process and the dilution process.

The cobalt and nickel separation method of the present invention is a method for separating cobalt and nickel from a lithium ion secondary battery, and includes a crushing and sorting step in which the lithium ion secondary battery is crushed and classified to obtain an electrode material containing at least cobalt, nickel, copper, and lithium; a leaching step in which a leachate is produced by the electrode material leaching method described in any one of claims 1 to 6; a copper precipitation step in which a hydrogen sulfide compound is added to the leachate and stirred to precipitate copper as copper sulfide; a first neutralization step in which an alkali metal hydroxide is added to the mixed liquid containing the precipitate obtained in the copper precipitation step to adjust the pH and obtain a first neutralization solution; and a solid-liquid separation of the first neutralization solution to separate cobalt and nickel. The method is characterized by comprising either a first treatment process including, in order, a first filtration process to obtain a first eluate containing nickel and a residue containing copper sulfide, or a second treatment process including, in order, a second filtration process to perform solid-liquid separation of a mixed liquid containing the precipitate obtained in the copper precipitation process to obtain a second eluate containing cobalt and nickel and a residue containing copper sulfide, and a second neutralization process to adjust the pH of the second eluate by adding an alkali metal hydroxide to obtain a second neutralized liquid; or a cobalt-nickel separation process to add a hydrogen sulfide compound to the first eluate obtained in the first treatment process or the second neutralized liquid obtained in the second treatment process, stir the mixture, and perform solid-liquid separation to obtain a precipitate containing cobalt sulfide and nickel sulfide and a residual liquid containing lithium.

In addition, the present invention may also perform the first treatment step as a subsequent step following the copper precipitation step.

The present invention may also include a heat treatment step, prior to the crushing and sorting step, in which the lithium-ion secondary battery is heated and subjected to heat treatment.

The present invention provides a method for leaching electrode materials that can efficiently leach electrode materials contained in lithium-ion secondary batteries in a short time without using an excessive amount of acid, and a method for separating cobalt and nickel that includes this leaching method.

1 is a flow chart showing the steps of a method for separating cobalt and nickel, including a method for leaching electrode materials, according to one embodiment of the present invention. 1 is a flowchart showing the steps of a method for separating cobalt and nickel, including a leaching method according to a second embodiment of the present invention. 1 is a graph showing an appropriate range of added sulfuric acid volume and concentration based on Equations 1 and 2.

Below, we will explain a method for leaching electrode materials according to one embodiment of the present invention, and a method for separating cobalt and nickel that includes this method, with reference to the drawings. Note that each of the embodiments shown below is provided as a specific explanation to better understand the spirit of the invention, and does not limit the present invention unless otherwise specified.

(First embodiment)
FIG. 1 is a flow chart showing the steps of a method for separating cobalt and nickel, including a method for leaching an electrode material according to a first embodiment of the present invention.

(Heat treatment step S1)
As a pretreatment process for separating the electrode materials that make up discarded lithium ion secondary batteries (hereinafter referred to as waste LIBs), a heating furnace is used to heat the waste LIBs with superheated steam to, for example, about 500°C, thereby performing heat treatment.

Heat treatment can be performed in a vacuum or at atmospheric pressure, but heating in an oxygen-free inert atmosphere is preferable. Due to the presence of binders and electrolyte, waste LIBs have strong adhesive forces between the positive and negative electrode active materials and the aluminum or copper foil current collectors. Therefore, heat treatment at 400°C or higher facilitates separation of these active materials from the current collectors. By setting the heating temperature of waste LIBs to 650°C or below, it is possible to prevent the aluminum from melting and enveloping the active material, which would then solidify upon cooling, making it difficult to extract the active material alone.

(Crushing and sorting step S2)
Next, the waste LIB after the heat treatment is crushed, and then the electrode material is separated by sieving. The crushing of the waste LIB is performed using, for example, a biaxial shear crusher or a hammer mill.

The crushed waste LIB is then classified using a sieve with appropriate mesh size, and the battery container, aluminum foil, copper foil, and nickel terminals are collected as the upper product of the sieve, while the electrode material containing the positive electrode active material (e.g., _LiCoO2 ) and the negative electrode active material (graphite) is collected as the lower product. Such electrode material may be one that passes through a sieve with mesh size of about 0.5 mm, for example.

The separated electrode material mainly contains the constituent materials of the positive electrode active material and impurities such as cobalt, nickel, manganese, copper, iron, aluminum, lithium, and calcium, as well as the constituent materials of the negative electrode active material such as carbon.

(Leaching step S3)
Next, in the leaching step S3 constituting the leaching method for an electrode material of this embodiment, the electrode material separated in the crushing and sorting step S2 is subjected to acid leaching with a treatment liquid containing sulfuric acid to obtain a leachate.
The leaching step S3 is carried out in two stages: a kneading step S3-1 in which the electrode material is kneaded with a small amount of sulfuric acid (treatment liquid) to form a leaching paste, and a dilution step S3-2 in which the obtained leaching paste is diluted with water to form a leaching solution.

In the kneading step S3-1, the electrode material is kneaded with a small amount of sulfuric acid, for example, with a concentration of approximately 45 to 47% by mass. Specifically, for example, the electrode material is placed in a container, a small amount of sulfuric acid is added, and the electrode material and sulfuric acid are then kneaded using a rubber spatula, glass rod, or the like until they form a paste. At this time, the kneaded mixture will foam due to the gas generated when the electrode material is dissolved by the sulfuric acid, but it is preferable to knead the mixture in a way that physically breaks up the bubbles that have formed. Note that kneading can also be performed using a kneader with a degassing function, such as a vacuum kneader.

In the kneading process S3-1, kneading in a paste state makes it easier for the electrode material to come into contact with sulfuric acid than with conventional liquid stirring. Furthermore, the kneading process breaks down any air bubbles that may have formed during leaching, making it easier for the electrode material and sulfuric acid to blend together. This allows the electrode material to be acid-leached efficiently in a short amount of time.

The mixing ratio of the electrode material used in the kneading step S3-1 to the sulfuric acid added thereto is preferably such that the following formulas 1 and 2 are satisfied, where EA is the mass (g) of the electrode material, SV is the volume (mL) of the sulfuric acid, and SC is the concentration (mol/L) of the sulfuric acid.
1≦(SV/EA)≦2...(1)
5.5EA≦(SC×SV)≦10.3EA...(2)

If the SV/EA ratio in Equation 1 is less than 1, the kneaded product will be too hard and difficult to turn into a paste-like kneaded product (leached paste). On the other hand, if the SV/EA ratio is more than 2, the fluidity will be too high and the product will become liquid.

Furthermore, if SC x SV in Equation 2 is less than 5.5 EA, there will not be enough sulfate ions to fully leach the active material contained in the electrode material. On the other hand, if SC x SV exceeds 10.3 EA, there will be an excess of sulfate ions, i.e., too much sulfuric acid will not contribute to leaching, which could result in unnecessary processing costs.

Figure 3 shows a graph illustrating the appropriate range of sulfuric acid addition amount and concentration based on Equations 1 and 2. In Figure 3, EA = 1. As Figure 3 shows, by keeping the sulfuric acid addition amount and concentration within the appropriate range, it is possible to form a leaching paste, sufficiently leach the active material contained in the electrode material, and reduce the amount of sulfuric acid unnecessary for the reaction.

In the kneading step S3-1, sulfuric acid is added to the electrode material, and hydrogen peroxide may also be added.
The Co and Ni contained in the electrode material include trivalent and tetravalent Co and Ni that are difficult to dissolve in sulfuric acid, so adding hydrogen peroxide as a reducing agent can reduce them to divalent Co and Ni that are more easily soluble in sulfuric acid. Hydrogen peroxide may be added in the form of a hydrogen peroxide solution with a concentration of 30 to 35 mass %.

When hydrogen peroxide is added in the kneading step S3-1, it is preferable to set the temperature of the kneaded mixture to 50° C. or higher in order to exert the reducing properties of hydrogen peroxide. If the temperature is lower than 50° C., the reaction time will be long, and if the temperature is higher than 60° C., more heat than necessary will be added, resulting in a waste of thermal energy.
In the kneading step S3-1, when sulfuric acid is added to the electrode material, the temperature of the kneaded mixture is often higher than room temperature due to the positive heat of reaction, so that, depending on the conditions, external heating may not be necessary.

Alcohol can also be added in the kneading step S3-1. Examples of alcohols that can be added include saturated, straight-chain alcohols with eight or fewer carbon atoms, such as ethanol and butanol. The presence of hydrophobic and hydrophilic groups in such alcohols increases the affinity between the hydrophobic electrode active material and the aqueous sulfuric acid, facilitating kneading. Furthermore, their antifoaming properties reduce foaming during kneading, making it easier to form a kneaded paste.

In the dilution step S3-2, water, such as distilled water, is added to the leaching paste obtained in the kneading step S3-1 and stirred to produce a leachate. At this time, if the leachate is diluted so that its pH is 2.0 or less, the components of the electrode material that are soluble in sulfuric acid will be almost completely dissolved.

If the pH of the leachate exceeds 2 when the leaching paste is diluted with water in the dilution step S3-2, it is preferable to further add sulfuric acid to adjust the pH so that it is 2.0 or less. If the pH of the leachate is kept at 2 or less, there is no need to adjust the pH in the subsequent copper separation step S4.

Hydrogen peroxide can also be added in the dilution step S3-2. When adding hydrogen peroxide in the dilution step S3-2, it is preferable to set the temperature of the leaching solution in the range of 50°C or higher and 60°C or lower to maximize the reducing properties of the hydrogen peroxide. If the temperature is below 50°C, the reaction time will be longer, and if it exceeds 60°C, more heat than necessary will be added, resulting in a waste of thermal energy. It is also preferable to add hydrogen peroxide only after the pH of the leaching solution has reached 2.0 or lower.

By adding hydrogen peroxide in the dilution step S3-2, trivalent and tetravalent Co and Ni contained in the electrode material are reduced to divalent Co and Ni, which are easily soluble in sulfuric acid, thereby increasing the solubility of Co and Ni. The hydrogen peroxide can be added in the form of an aqueous solution, i.e., a hydrogen peroxide solution with a concentration of 30 to 35% by mass.

By performing the leaching step S3 described above, it is possible to obtain a leaching solution with a pH of 2.0 or less, in which the active material of the electrode material has been leached. Note that the carbon contained in the electrode material is not leached, and therefore remains in a solid state as a carbon residue.

As described above, according to the electrode material leaching method of this embodiment, the leaching process S3 involves two steps: the kneading step S3-1 and the dilution step S3-2. This allows the electrode material to be acid-leached efficiently in a short time without using an excessive amount of sulfuric acid.

(Copper precipitation step S4)
Next, a hydrogen sulfide compound is added to the leachate obtained in the leaching step S3 and stirred to obtain a mixture of an eluate containing cobalt and nickel and a precipitate containing copper sulfide (CuS).

In the present invention, the hydrogen sulfide compound means a compound that contains sulfur and in which the sulfur content takes the form of H ₂ S, HS ^- or S ^{2 -} when dissolved in water.
The hydrogen sulfide compound used in the copper separation step S4 is a water-soluble alkali metal hydrogen sulfide, and in this embodiment, an aqueous solution of sodium hydrogen sulfide (NaSH) is used. In a specific example of the copper separation step S4, the leachate is diluted with ion-exchanged water, and then an aqueous solution of sodium hydrogen sulfide is added to the diluted leachate and stirred.

The aqueous solution of sodium hydrogen sulfide is added, for example, until the oxidation-reduction potential (vs. Ag/AgCl) falls below 0 mV. By adding sodium hydrogen sulfide until the oxidation-reduction potential falls below 0 mV, it is possible to precipitate almost all of the copper contained in the leachate.

It is preferable to maintain the pH of the leaching solution at 2.0 or less from the start to the end of the addition of the hydrogen sulfide compound. If the pH of the leaching solution exceeds 2.0, sulfides of cobalt and nickel may be produced, which may reduce the recovery rate of these metals in the eluate.
The hydrogen sulfide compound may be, for example, sodium sulfide, sodium thiosulfate, or sodium dithionite, in addition to sodium hydrogen sulfide.

By adding a hydrogen sulfide compound to the leachate, the copper and sulfur dissolved in the leachate react to form copper sulfide (CuS), which precipitates. Meanwhile, the metal components excluding copper (cobalt, nickel, manganese, iron, aluminum, lithium, calcium, etc.) remain in the liquid phase, resulting in an eluate containing cobalt and nickel.

(First processing step S5A)
Next, as the first treatment step S5A, a first neutralization step S5A-1 and a first filtration step S5A-2 are carried out in this order.
In the first neutralization step S5A-1, an alkali metal hydroxide is added to the mixed solution containing the precipitate obtained in the copper precipitation step S4 to adjust the pH, thereby obtaining a first neutralized solution.

In the upstream copper precipitation process S4, the pH of the leachate is maintained at 2.0 or below from the start to the end of the addition of the hydrogen sulfide compound. If this continues, there is a risk that the hydrogen sulfide compound will not react with cobalt and nickel in the downstream cobalt-nickel separation process S6. However, the pH of the leachate decreases as the hydrogen sulfide compound is added. If the pH is below 3.0 at the start of the addition of the hydrogen sulfide compound after pH adjustment, an excessive decrease in pH will occur before the addition of the hydrogen sulfide compound is completed, requiring further pH adjustment. For this reason, it is more efficient to maintain the pH at 3.0 or above in the process prior to the cobalt-nickel separation process S6.

Furthermore, if the pH is adjusted to a value above 4.0, it takes time to adjust the pH, and adding the hydrogen sulfide compound immediately drops the pH to 4.0 or below, making this an inefficient process. Therefore, the pH adjustment range is preferably between 3.0 and 4.0.

In addition, in this first neutralization step S5A-1, sodium hydroxide (NaOH) is used to adjust the pH of the mixed solution containing the precipitate obtained in the copper precipitation step S5 to approximately 3.0 to 4.0, so that the aluminum contained in this mixed solution can be converted into aluminum hydroxide (Al(OH) ₃ ) and precipitated.

In the first neutralization process S5A-1, which is the pH adjustment for pretreatment in the cobalt/nickel separation process S6, the pH adjustment solution can be sodium hydroxide (NaOH), potassium hydroxide (KOH), or even an acid such as sulfuric acid if the pH is above 4.0. In this embodiment, the pH of the eluate was adjusted to a range of 3.0 to 4.0, for example 3.5.

Next, in the first filtration step S5A-2, the first neutralized solution obtained in the first neutralization step S5A-1 is subjected to solid-liquid separation to separate a first eluate containing cobalt and nickel from a residue containing copper sulfide (CuS). As a result, the first eluate (liquid phase) is separated from the carbon residue produced in the leaching step S3, the precipitate residue containing copper sulfide (CuS) produced in the copper precipitation step S4, and a solid phase containing aluminum hydroxide (Al(OH) ₃ ) produced in the first neutralization step S5A-1. Saturated linear alcohols having 8 or less carbon atoms contained in the antifoaming agent used in the leaching step S3 are transferred to the first eluate.

In this embodiment, the carbon residue produced in the leaching process S3 is also filtered out by solid-liquid separation in the first filtration process S5A-2. However, by also performing solid-liquid separation in the leaching process S3, the carbon residue can be separated in advance before the first filtration process S5A-2 is performed.

The solid phase separated in the first filtration process S5A-2 can be repulped (purified by adding water to the solid phase to resuspend it and then dehydrating it) or the cake washed before being disposed of as waste.

(Cobalt/nickel separation step S6)
Next, by adding a water-soluble hydrogen sulfide compound to the first eluate obtained in the first treatment step S5A, the cobalt and nickel contained in the eluate become water-insoluble cobalt sulfide (CoS) and nickel sulfide (NiS), respectively, and are precipitated.

The hydrogen sulfide compound for sulfurizing the cobalt-nickel may be, for example, a water-soluble alkali metal hydrogen sulfide. The hydrogen sulfide compound may be the same as or different from that used in the copper precipitation step S4. In this embodiment, an aqueous solution of sodium hydrogen sulfide with a concentration of 200 g/L was used.
The aqueous solution of sodium hydrogen sulfide is added until the oxidation-reduction potential (vs. Ag/AgCl) becomes -400 mV or less. By adding sodium hydrogen sulfide until the oxidation-reduction potential becomes -400 mV or less, it is possible to precipitate almost all of the cobalt and nickel contained in the eluate.

The pH of the leaching solution from the start to the end of the addition of the hydrogen sulfide compound is preferably maintained within the range of 2.0 to 5.0, preferably 2.0 to 3.5. If the pH of the leaching solution falls below 2.0, a reaction occurs between sodium hydrogen sulfide and sulfuric acid (NaSH + _H2SO4 → _H2S + _Na2SO4 ), sodium hydrogen sulfide is consumed _, and sulfidation of cobalt and nickel becomes difficult. On the other hand, if the _pH of the leaching solution exceeds 5.0, hydroxides of other metals may be produced, which may reduce the purity of the precipitate. Furthermore, it is difficult to control the pH in the high range.

Cobalt sulfide herein may include cobalt sulfide compounds of various compositions, such as cobalt (II) sulfide, cobalt disulfide (CoS ₂ ), nonacobalt octasulfide (Co ₉ S ₈ ), etc. Similarly, nickel sulfide (NiS) may include nickel sulfide compounds of various compositions, such as nickel (II) sulfide, nickel disulfide (NiS ₂ ), trinickel tetrasulfide (Ni ₃ S ₄ ), trinickel disulfide (Ni ₃ S ₂ ), etc.

Meanwhile, the liquid phase (residual liquid) after adding the hydrogen sulfide compound contains metal components (manganese, iron, aluminum, lithium, calcium, etc.) excluding cobalt and nickel. The liquid phase obtained here can then be subjected to solvent extraction with pH adjustment to separate and recover the manganese, iron, aluminum, lithium, calcium, etc. contained therein.

(Remelting step S7)
Next, a redissolution liquid containing sulfuric acid is added to the precipitate obtained in the cobalt/nickel separation step S6, and the mixture is stirred, followed by solid-liquid separation to obtain a cobalt/nickel solution containing cobalt and nickel.

The re-dissolving liquid is, for example, a mixture of sulfuric acid and hydrogen peroxide as an oxidizing agent. One example of a re-dissolving liquid is a mixture of 100 ml of dilute sulfuric acid with a concentration of 1.5 mol/L and 20 ml of hydrogen peroxide solution with a concentration of 30 wt%.

In a specific example of the re-dissolving step S7, the precipitate is added to a re-dissolving solution heated to 60° C. or higher and immersed for 4 hours or more. It is preferable to further stir the solution. Alternatively, air bubbling can be performed when immersing the precipitate in the re-dissolving solution without adding hydrogen peroxide to the re-dissolving solution.
In this case, the dissolution rate of cobalt and nickel can be increased by setting the treatment solution temperature to 60°C or higher and the leaching time to 1 hour or longer. Although there are no particular limitations, the upper limit of the treatment solution temperature is 90°C and the upper limit of the leaching time is 15 hours, since further improvement in the dissolution rate cannot be expected at higher temperatures.

By treating the precipitate with this re-dissolution liquid, the cobalt and nickel dissolve in the re-dissolution liquid. Impurities that do not dissolve in the re-dissolution liquid, such as elemental sulfur produced in the cobalt-nickel separation step S6, remain as a solid phase. Subsequent solid-liquid separation using a filter or similar tool yields a cobalt-nickel solution with increased cobalt and nickel purity (refined).

The cobalt-nickel solution obtained in this way contains almost no other electrode material components (copper, iron, aluminum, lithium, calcium, etc.) other than cobalt and nickel, making it suitable as a highly pure recovered raw material for cobalt and nickel.

It is also preferable to remove impurities other than cobalt sulfide and nickel sulfide by repulping the precipitate as a step preceding the redissolving step S7.
Although the procedure for removing aluminum before performing solid-liquid separation in the copper precipitation step S4 has been described above, if such a procedure is not performed, the precipitate may contain aluminum compounds. In this case, the aluminum compounds can be removed by repulping the precipitate.

(Solvent extraction step S8)
Next, an extractant solution is added to the cobalt-nickel solution obtained in the redissolution step S7 to obtain a cobalt extract and a nickel extract.
The extractant solution may be a mixed solution of a metal extractant and a diluent, such as a mixed solution of 20 vol% 2-ethylhexyl 2-ethylhexylphosphonate (PC88A, manufactured by Daihachi Chemical Co., Ltd.) and 80 vol% kerosene (diluent).

Using the above-mentioned extractant solution, a cobalt sulfate (CoSO ₄ ) solution and a nickel sulfate (NiSO ₄ ) solution are separated and recovered from the cobalt-nickel solution by a mixer-settler.

The above process allows for the recovery of cobalt and nickel from waste LIBs in high yields. For example, if the amounts of cobalt and nickel in the electrode material extracted from waste LIBs are each 100%, the cobalt and nickel separation method of this embodiment allows for the recovery of cobalt and nickel in high yields of 90% by mass or more.

Second Embodiment
FIG. 2 is a flow chart showing the steps of a method for separating cobalt and nickel according to a second embodiment of the present invention.
In the second embodiment described below, the same steps as those in the first embodiment will not be described.

In the second embodiment, a second treatment step S5B is carried out between the copper precipitation step S4 and the cobalt/nickel separation step S6, instead of the first treatment step.
As the second treatment step S5B, a second filtration step S5B-1 and a second neutralization step S5B-2 are carried out in this order.

In the second filtration process S5B-1, solid-liquid separation is performed on the mixed liquid containing the precipitate obtained in the copper precipitation process S4, separating the first eluate containing cobalt and nickel from a residue containing copper sulfide (CuS). This separates the solid phase containing the carbon residue produced in the leaching process S3 and the precipitate residue containing copper sulfide (CuS) produced in the copper precipitation process S4 from the second eluate (liquid phase).

The solid phase separated in the second filtration process S5B-1 can be repulped (purified by adding water to the solid phase to resuspend it and then dehydrating it) or the cake washed before being disposed of as waste.

In the second neutralization process S5B-2, an alkali metal hydroxide is added to the second eluate obtained in the second filtration process S5B-1 to adjust the pH, thereby obtaining a second neutralized solution.

In the upstream copper precipitation process S4, the pH of the leachate is maintained at 2.0 or below from the start to the end of the addition of the hydrogen sulfide compound. If this continues, there is a risk that the hydrogen sulfide compound will not react with cobalt and nickel in the downstream cobalt-nickel separation process S6. However, the pH of the leachate decreases as the hydrogen sulfide compound is added. If the pH is below 3.0 at the start of the addition of the hydrogen sulfide compound after pH adjustment, an excessive decrease in pH will occur before the addition of the hydrogen sulfide compound is completed, requiring further pH adjustment. For this reason, it is more efficient to maintain the pH at 3.0 or above in the process prior to the cobalt-nickel separation process S6.

Furthermore, if the pH is adjusted to a value above 4.0, it takes time to adjust the pH, and adding the hydrogen sulfide compound immediately drops the pH to 4.0 or below, making this an inefficient process. Therefore, the pH adjustment range is preferably between 3.0 and 4.0.

In addition, in this second neutralization step S5B-2, sodium hydroxide (NaOH) is used to adjust the pH of the second eluate obtained in the second filtration step S5B-1 to about 3.0 to 4.0, so that the aluminum contained in this second eluate can be converted into aluminum hydroxide (Al(OH) ₃ ) and precipitated.

In the second neutralization process S5B-2, which is the pH adjustment for pretreatment in the cobalt/nickel separation process S6, the pH adjustment liquid for adjusting the eluate to a pH of 3.0 to 4.0 can be sodium hydroxide (NaOH) or potassium hydroxide (KOH) if the pH is below 3.0, or an acid such as sulfuric acid if the pH is above 4.0. In this embodiment, a 25 wt% aqueous sodium hydroxide solution was used to adjust the pH of the second eluate to a range of 3.0 to 4.0, for example, 3.5.

Although the above describes embodiments of the present invention, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be embodied in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included within the scope of the invention and its equivalents as set forth in the claims, as well as within the scope and spirit of the invention.

The effectiveness of the cobalt and nickel separation method using the electrode material leaching method of the present invention was verified.
Example 1
72.5 g of electrode material (electrode active material) extracted from waste LIB was added to 85 mL of 47 wt % sulfuric acid and kneaded with a rubber spatula for 15 minutes to obtain a leached paste (kneading process). Table 1 shows the leaching test results for the electrode material (electrode active material) after the kneading process. The time (min) in Table 1 indicates the elapsed time from the start of hydrogen peroxide addition. In addition, the pH, temperature, and ORP (oxidation-reduction potential) in the table indicate the values at each time point, the cumulative added amount (sulfuric acid, hydrogen peroxide, NaSH, NaOH) indicates the total added amount at each time point, and the concentration indicates the metal concentration at each time point.

Thereafter, 415 mL of distilled water was added to the obtained leached paste to dilute it (dilution step), and the liquid temperature was adjusted to about 50°C while stirring (Experimental Example A1).
For Experimental Example A1, the change over time from the start of addition of 30 wt % hydrogen peroxide was confirmed, and 25 mL of 30 wt % hydrogen peroxide was added over 75 minutes while maintaining the pH at 2.0 or less by adding 47 wt % sulfuric acid appropriately (Experimental Example A2).
To Experimental Example A2, a 200 g/L sodium hydrosulfide solution was added until the ORP became 0 mV or less (copper separation step, Experimental Example A3).
For Experimental Example A3, a 25 wt % sodium hydroxide solution was added to the leachate to neutralize it and stabilize the pH at 3.0 to 4.0 (neutralization step, Experimental Example A4).
In Experimental Example A4, the carbon from the negative electrode material of the waste LIB, which was insoluble during sulfuric acid leaching, and the resulting residue (copper sulfide) were subjected to solid-liquid separation by filtration to obtain 462 mL of leaching solution. The composition of 36.96 g of the residue (copper sulfide) is shown in Table 2.

The results of Experimental Example 1 showed that when the cobalt and nickel in the electrode material extracted from the waste LIB were taken as 100%, the leaching rate was calculated to be 95% for cobalt and 95% for nickel. This confirmed that the cobalt and nickel were sufficiently leached from the active material, and that it was possible to reduce the time and amount of sulfuric acid required for leaching compared to conventional methods.

Next, after confirming that a sufficient amount of black precipitate (cobalt sulfide and nickel sulfide) had been produced, the precipitate was recovered by solid-liquid separation (cobalt-nickel separation process). Meanwhile, the remaining liquid contained impurities such as manganese, aluminum, iron, lithium, and calcium, and was disposed of as metal-containing waste liquid.

The precipitate was added to a redissolution solution of 100 mL of 1.5 mol/L sulfuric acid and 20 mL of 30 wt% hydrogen peroxide, heated to a liquid temperature of 60°C, and stirred for 1 hour (redissolution process). After cooling to room temperature, the undissolved matter and the elemental sulfur produced in the reaction in the previous process were removed by filtration.

The cobalt-nickel solution obtained in this manner was separated and recovered as a cobalt sulfate solution and a nickel sulfate solution using a mixer-settler with an extractant solution consisting of a mixture of 20 vol% PC88A (manufactured by Daihachi Chemical Co., Ltd.) metal extractant and 80 vol% kerosene (solvent extraction process).

In the procedure of Example 1 described above, when the cobalt and nickel in the electrode material extracted from waste LIB were taken as 100%, the cobalt and nickel obtained in the stripped solution by solvent extraction were 93% and 93%, respectively. Therefore, it was confirmed that the method for separating cobalt and nickel equipped with the electrode material leaching method of this embodiment can recover cobalt and nickel from waste LIB with a high yield.
The metal concentration was measured by ICP-AES, pH by a pH meter, and ORP by an ORP meter. The percentage values are based on mass.

Example 2
29.0 g of electrode material (electrode active material) extracted from waste LIB was added with 40 mL of 47 wt % sulfuric acid and kneaded with a rubber spatula for 15 minutes to obtain a leached paste (kneading process). 10 mL of 30 wt % hydrogen peroxide was added to the leached paste and kneaded with a rubber spatula for 5 minutes (kneading process of Example 2).
Table 3 shows the results of the leaching test of the electrode material (electrode active material) after the kneading process of Example 2. The time (min) in Table 3 indicates the elapsed time from the addition of distilled water in the dilution process. In addition, the pH, temperature, and ORP in the table indicate the values at each time point, the cumulative added amount (sulfuric acid, hydrogen peroxide, NaSH, NaOH) indicates the total added amount at each time point, and the concentration indicates the metal concentration at each time point.

Thereafter, the obtained leached paste was diluted with 160 mL of distilled water (dilution step), and then stirring was started (Experimental Example B1).
The solution in Experimental Example B1 was stirred for 30 minutes at a liquid temperature of about 50° C. while ensuring that the pH was 2.0 or less (Experimental Example B2).
To Experimental Example B2, a 200 g/L sodium hydrosulfide solution was added until the ORP became 0 mV or less (copper separation step, Experimental Example B3).
For Experimental Example B3, a 25 wt % sodium hydroxide solution was added to the leachate to neutralize it and stabilize the pH at 3.0 to 4.0 (neutralization step, Experimental Example B4).
For Experimental Example B4, the carbon from the negative electrode material of the waste LIB, which was insoluble during sulfuric acid leaching, and the resulting residue (copper sulfide) were subjected to solid-liquid separation by filtration, yielding 175 mL of leachate. The composition of 14.41 g of the residue (copper sulfide) is shown in Table 4. When the leaching rates are calculated assuming that the cobalt and nickel in the electrode material extracted from the waste LIB are 100%, 95% of cobalt and 95% of nickel have been leached, indicating that the cobalt and nickel have been sufficiently leached from the active material.

(Comparative Example)
14.5 g of electrode material (electrode active material) extracted from waste LIB was added to 100 mL of sulfuric acid solution containing 31 mL of sulfuric acid at a concentration of 47 wt% and stirred. Then, the liquid temperature was increased to 60°C, and 10 mL of hydrogen peroxide at a concentration of 30 wt% was added. Leaching was carried out for 4 hours, followed by solid-liquid separation by filtration to obtain a leachate. The leaching yields were 98% or higher for both cobalt and nickel.

Comparative Example: Leaching took 4 hours, but it was confirmed that Example 1 achieved cobalt and nickel leaching rates comparable to those of the conventional comparative examples in a shorter time of 75 minutes (Experimental Example A2) and 30 minutes in Example 2.

The cobalt and nickel separation method incorporating the electrode material leaching method of the present invention enables the accurate separation and recovery of valuable metals contained in used lithium-ion secondary batteries, particularly cobalt and nickel, from other metals, thereby enabling the efficient production of highly pure recycled resources from lithium-ion secondary batteries. Therefore, it has industrial applicability.

Claims (9)

A method for leaching an electrode material of a lithium ion secondary battery with acid, comprising:
a leaching step of reacting an electrode material of a lithium ion secondary battery with sulfuric acid to obtain a leachate by leaching out metals contained in the electrode material,
the leaching step includes a kneading step of kneading the sulfuric acid and the electrode material to form a leaching paste, and a dilution step of adding water to the leaching paste to dilute it;
In the kneading step, when the mass (g) of the electrode material is EA, the volume (mL) of the sulfuric acid is SV, and the concentration (mol/L) of the sulfuric acid is SC, kneading is performed so that the following relationships are satisfied: 1≦(SV/EA)≦2 and 5.5EA≦(SC×SV)≦10.3EA . 2. The method for leaching an electrode material according to claim 1, wherein no external heating operation is performed during the kneading process. The electrode material leaching method described in claim 1 or 2, characterized in that hydrogen peroxide is further added during at least one of the kneading process and the dilution process. The electrode material leaching method described in claim 1 or 2, characterized in that during the dilution process, the temperature of the diluted solution is adjusted to a range of 50°C or higher and 60°C or lower, and the pH is adjusted to 2.0 or lower, and then hydrogen peroxide is added. The electrode material leaching method described in any one of claims 1 to 4, characterized in that the dilution process further includes a process of adding sulfuric acid so that the pH of the diluted leaching solution is 2.0 or less. The electrode material leaching method described in any one of claims 1 to 5, characterized in that alcohol is further added during at least one of the kneading process and the dilution process. A method for separating cobalt and nickel from a lithium ion secondary battery, comprising:
a crushing and sorting step of crushing and classifying the lithium ion secondary battery to obtain an electrode material containing at least cobalt, nickel, copper, and lithium;
a leaching step for producing a leachate by the method for leaching an electrode material according to any one of claims 1 to 6;
a copper precipitation step in which a hydrogen sulfide compound is added to the leachate and stirred to precipitate copper as copper sulfide;
a first treatment step including, in order, a first neutralization step of adjusting the pH of a mixed solution containing the precipitate obtained in the copper precipitation step by adding an alkali metal hydroxide to obtain a first neutralized solution, and a first filtration step of performing solid-liquid separation of the first neutralized solution to obtain a first eluate containing cobalt and nickel and a residue containing copper sulfide; or
a second treatment step including, in order, a second filtration step in which a mixed solution containing the precipitate obtained in the copper precipitation step is subjected to solid-liquid separation to obtain a second eluate containing cobalt and nickel and a residue containing copper sulfide, and a second neutralization step in which an alkali metal hydroxide is added to the second eluate to adjust the pH to obtain a second neutralized solution;
a cobalt/nickel separation step in which a hydrogen sulfide compound is added to the first eluate obtained in the first treatment step or the second neutralized solution obtained in the second treatment step, and the mixture is stirred and subjected to solid-liquid separation to obtain a precipitate containing cobalt sulfide and nickel sulfide and a residual solution containing lithium;
A method for separating cobalt and nickel, comprising: The cobalt and nickel separation method described in claim 7, characterized in that the first treatment step is carried out as a subsequent step to the copper precipitation step. The method for separating cobalt and nickel according to claim 7 or 8, characterized in that it includes a heat treatment step in which the lithium ion secondary battery is heated and subjected to heat treatment as a pre-processing step of the crushing and sorting step.