JP7106121B2 - Cobalt recovery method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a cobalt recovery method for recovering cobalt from a liquid to be treated in which at least cobalt and impurity metals are dissolved, and particularly to a cobalt recovery method used for recovering cobalt from waste lithium ion batteries.

Lithium-ion batteries are attracting attention as lightweight and high-energy-density batteries, and are widely used as batteries for various mobile devices, electric vehicles, power-assisted bicycles, and the like. Lithium transition metal oxides such as lithium cobalt oxide are used as positive electrode active materials in the positive electrodes of these lithium ion batteries. is extremely important from

As a method for recovering cobalt from waste lithium ion batteries, for example, Patent Document 1 discloses that waste lithium ion batteries are leached with sulfuric acid to elute cobalt, and alkali is added to the acid eluate to adjust the pH to 4 to 5. After adjusting and depositing and precipitating the salt of the impurity metal such as aluminum eluted with cobalt as crystals, the pH is further adjusted to 7 to 10 by adding an alkali, and the cobalt salt is deposited and precipitated as crystals. A method for recovering cobalt is described.

Japanese Patent No. 5077788

However, in the above-described method, the pH of the acid eluate is set to 4 or more in order to remove impurity metals such as aluminum from the acid eluate. Cobalt may be precipitated and precipitated to be removed from the acid eluate together with the impurity metals, resulting in a low cobalt recovery rate during the subsequent cobalt recovery.

The present invention has been made to solve the above problems, and an object thereof is to provide a cobalt recovery method capable of recovering cobalt from a liquid to be treated in which cobalt and impurity metals are dissolved at a high recovery rate.

As a result of intensive studies aimed at solving the above problems, the present inventor found that when the salt of the impurity metal is precipitated as crystals by adjusting the pH of the liquid to be treated in which at least cobalt and impurity metals are dissolved, It has been found that when the concentration of the aqueous alkali solution added to the liquid is high, cobalt salt crystals are precipitated together with the impurity metal salt crystals, and cobalt is removed from the liquid to be treated together with the impurity metals. The present invention was completed as a result of further studies based on such findings. That is, the present invention provides a method for recovering cobalt in the following aspects.

In the cobalt recovery method of the present invention, an alkaline aqueous solution is added to an acidic treatment liquid in which at least cobalt and impurity metals are dissolved to adjust the pH to 4 to 6, thereby precipitating a salt of the impurity metals as crystals. A first pH adjustment step, a first solid-liquid separation step of separating a precipitate containing impurity metal salt crystals precipitated in the first pH adjustment step from the liquid to be treated, and a treatment to be treated after the first solid-liquid separation step A second pH adjustment step of precipitating cobalt salt crystals by adding an alkaline aqueous solution to the liquid to adjust the pH to 7 to 11, and a precipitate containing the cobalt salt crystals precipitated in the second pH adjustment step. and a second solid-liquid separation step of separating from the liquid to be treated, and the alkali concentration of the aqueous alkali solution added in the first pH adjustment step is less than 1.0 mol/L.

In the cobalt recovery method of the present invention, it is preferable that the alkali concentration of the alkali aqueous solution added in the first pH adjustment step is 0.1 mol/L or more.

Further, in the method for recovering cobalt of the present invention, in the first pH adjustment step, an alkaline aqueous solution having an alkali concentration of 1.0 mol/L or more is applied until the pH of the liquid to be treated reaches a predetermined value lower than 4. It is preferable to add an alkaline aqueous solution having an alkali concentration of less than 1.0 mol/L to the liquid to be treated to adjust the pH of the liquid to be treated to 4-6.

Further, in the cobalt recovery method of the present invention, lithium is dissolved in the liquid to be treated, and a concentration step of evaporating and concentrating the liquid to be treated after the second solid-liquid separation step; and a carbonation step of mixing carbon dioxide gas and/or adding a water-soluble carbonate.

Further, in the cobalt recovery method of the present invention, a third solid-liquid separation step of separating a precipitate containing lithium carbonate crystals precipitated in the carbonation step from the liquid to be treated, and after the third solid-liquid separation step an electrodialysis step of separating and recovering alkali from the liquid to be treated by subjecting the liquid to be treated to bipolar membrane electrodialysis, wherein the alkali recovered in the electrodialysis step is added to the first pH adjusting step; And/or it is preferable to reuse it as an alkali used in the second pH adjustment step.

According to the method for recovering cobalt of the present invention, the alkali concentration is less than 1.0 mol/L when removing the impurity metal from the liquid to be treated in the first pH adjustment step with respect to the liquid to be treated in which cobalt and impurity metals are dissolved. By adjusting the pH of the liquid to be treated with a dilute aqueous alkali solution, removal of cobalt together with impurity metals from the liquid to be treated can be suppressed. Therefore, the amount of cobalt in the liquid to be treated supplied to the second pH adjustment step can be maintained high, so that cobalt can be recovered at a high recovery rate in the second pH adjustment step.

It is a flow chart which shows roughly the procedure of the cobalt recovery method of one embodiment of the present invention. FIG. 2 is a schematic diagram showing a schematic configuration of a processing apparatus used in the cobalt recovery method of FIG. 1; 1 is a schematic diagram showing a schematic configuration of a bipolar membrane electrodialyzer; FIG. 4 is a flowchart schematically showing procedures of a cobalt recovery method according to another embodiment of the present invention; 5 is a schematic diagram showing a schematic configuration of a processing apparatus used in the cobalt recovery method of FIG. 4. FIG. 4 is a flowchart schematically showing procedures of a cobalt recovery method according to another embodiment of the present invention; 7 is a schematic diagram showing a schematic configuration of a processing apparatus used in the lithium recovery method of FIG. 6. FIG. FIG. 8 is a schematic diagram showing a schematic configuration of the bipolar membrane electrodialyzer of FIG. 7; 4 is a flow chart schematically showing procedures of a method for recovering lithium according to another embodiment of the present invention; FIG. 10 is a schematic diagram showing a schematic configuration of a processing apparatus used in the lithium recovery method of FIG. 9; 4 is a photograph of the surface state of the filtration residue of Example 1. FIG. 4 is a photograph of the surface state of the filtration residue of Example 2. FIG. It is the photograph which image|photographed the surface state of the filtration residue of a comparative example.

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows the procedure of each step of a cobalt recovery method according to one embodiment of the present invention, and FIG. 2 shows a schematic configuration of a processing apparatus 10 that implements the cobalt recovery method. The cobalt recovery method of the present embodiment will be described with an example of recovering lithium in addition to cobalt from waste lithium ion batteries.

The cobalt recovery method of this embodiment is
- an acid elution step S1 of leaching waste lithium ion batteries with an inorganic acid to dissolve cobalt and lithium;
- a solid-liquid separation step S2 for separating an insoluble residue from the liquid to be treated obtained by the acid elution step S1;
- a first pH adjustment step S3 of adding an alkaline aqueous solution to the liquid to be treated after the solid-liquid separation step S2 to adjust the pH to 4 to 6;
- A solid-liquid separation step S4 (corresponding to the "first solid-liquid separation step" described in the claims) for separating the precipitate containing impurity metal salt crystals deposited in the first pH adjustment step S3 from the liquid to be treated. When,
- a second pH adjustment step S5 of adding an alkaline aqueous solution to the liquid to be treated after the solid-liquid separation step S4 to adjust the pH to 7 to 11;
- a solid-liquid separation step S6 (corresponding to the "second solid-liquid separation step" in the claims) for separating the precipitate containing cobalt salt crystals deposited in the second pH adjustment step S5 from the liquid to be treated;
- a concentration step S7 for evaporating and concentrating the liquid to be treated after the solid-liquid separation step S6;
- a carbonation step S8 of mixing carbon dioxide and/or adding a water-soluble carbonate to the liquid to be treated after the concentration step S7;
- a solid-liquid separation step S9 (corresponding to the "third solid-liquid separation step" in the claims) for separating the precipitate containing lithium carbonate crystals deposited in the carbonation step S8 from the liquid to be treated;
- An electrodialysis step S10 of separating and recovering an alkali and an inorganic acid containing at least lithium hydroxide from the liquid to be treated by subjecting the liquid to be treated after the solid-liquid separation step S9 to bipolar membrane electrodialysis;
have

The waste lithium-ion batteries subject to cobalt recovery are used lithium-ion batteries whose charge capacity has decreased due to the prescribed number of charge-discharge cycles, as well as semi-finished products and product specifications that occur due to defects in the battery manufacturing process. Including old model inventory items that occur due to change. The waste lithium ion battery may be pulverized or roasted, or may be a powder obtained by pulverizing and roasting.

First, in the acid elution step S1, metals such as aluminum, nickel, and iron are eluted in addition to cobalt and lithium by leaching the above-mentioned waste lithium ion battery with an inorganic acid. Examples of inorganic acids that can be used include sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid. In the present embodiment, sulfuric acid is used because of its low cost and ease of handling.

In the acid leaching step S1, the method of leaching the waste lithium ion battery with an inorganic acid is not particularly limited, and a commonly used method can be used. For example, the waste lithium ion battery is immersed in an aqueous solution of an inorganic acid such as an aqueous sulfuric acid solution in the acid dissolution tank 1 and stirred for a predetermined period of time to obtain an acidic liquid to be treated in which metals such as cobalt are dissolved. In the acid elution step S1, the concentration of the inorganic acid in the aqueous solution is preferably 1 mol /L to 5 mol/L, and the temperature of the aqueous solution is preferably 60° C. or higher.

In the next solid-liquid separation step S2, the insoluble residue is separated from the liquid to be treated by filtering the liquid to be treated obtained in the acid elution step S1. The insoluble residue is mainly carbon materials, metal materials, and organic materials that are insoluble in inorganic acids. As a method for solid-liquid separation, for example, known devices such as various filtration devices such as pressure filtration (filter press), vacuum filtration, and centrifugal filtration, and centrifugal separators such as a decanter type can be used. The same applies to the solid-liquid separation steps S4, S6, and S9 below.

In the next first pH adjustment step S3, an alkaline aqueous solution is added to the liquid to be treated (filtrate) after the solid-liquid separation step S2 to adjust the pH to 4-6, preferably 4-5. As a result, among the above metals in the liquid to be treated, impurity metals (for example, aluminum and iron) are removed from the liquid to be treated. As the alkali, sodium hydroxide, potassium hydroxide, lithium hydroxide, or the like can be used, and lithium hydroxide is used in this embodiment.

In the first pH adjustment step S3, the method for adjusting the pH of the liquid to be treated is not particularly limited, and a commonly used method can be used. For example, by adding an alkaline aqueous solution such as an aqueous lithium hydroxide solution while stirring the liquid to be treated in the first pH adjustment tank 2, impurity metals in the liquid to be treated are removed by hydroxides (e.g. aluminum hydroxide, water Precipitates and precipitates as crystals of inorganic salts such as iron oxide). The first pH adjustment step S3 is preferably carried out while heating the lithium-containing liquid to a constant temperature, for example, 30°C to 60°C.

The alkali aqueous solution added in the first pH adjustment step S3 has a dilute alkali concentration of less than 1.0 mol/L. As will be described later in detail, this makes it possible to prevent the cobalt in the liquid to be treated from precipitating and precipitating as cobalt salt crystals together with the impurity metals and being removed from the liquid to be treated in the first pH adjustment step S3. However, if the alkali concentration is excessively low, it is necessary to use a large amount of aqueous alkali solution for pH adjustment in the first pH adjustment step S3, and the amount of the liquid to be treated after pH adjustment becomes large. The lower limit of the alkali concentration is preferably 0.1 mol/L or more. In order to effectively suppress the removal of cobalt in the liquid to be treated in the first pH adjustment step S3, the alkali concentration of the aqueous alkali solution added in the first pH adjustment step S3 is It is preferably 0.5 mol/L or less, more preferably 0.2 mol/L or less.

In this first pH adjustment step S3, in order to reduce the amount of the aqueous alkali solution used for pH adjustment, a high alkali concentration of 1.0 mol/L or more is maintained until the pH of the liquid to be treated reaches a predetermined value smaller than 4. is added to the liquid to be treated, and after the pH of the liquid to be treated reaches a predetermined value, an aqueous alkali solution having a weak alkali concentration of less than 1.0 mol/L is added to the liquid to be treated. , the pH of the liquid to be treated can be adjusted to 4-6. The predetermined value of the pH of the liquid to be treated can be set within the range of 2-3.

The precipitate deposited and precipitated in the first pH step S3 is separated from the liquid to be treated by filtering the liquid to be treated in the next solid-liquid separation step S4. In addition, copper etc. may be contained in the impurity metal removed from the to-be-processed liquid by 1st pH process S3. In the solid-liquid separation step S4, it is preferable to wash the precipitate with a washing liquid, and to circulate the washed waste liquid together with the liquid to be treated (filtrate) to the next second pH adjustment step S5. Thereby, the lithium contained in the washing waste liquid can be supplied to the second pH adjustment step S5 together with the lithium contained in the filtrate. The water used for washing the precipitate is not particularly limited, but it is preferable to use the condensed water generated when the liquid to be treated is evaporated and concentrated in the concentration step S7 described later. can be used effectively.

In the second pH adjustment step S5, an alkaline aqueous solution is added to the liquid to be treated (filtrate) after the solid-liquid separation step S4 to adjust the pH to 7-11, preferably 8-10. As a result, valuable metals such as cobalt and nickel among the above metals in the liquid to be treated are removed from the liquid to be treated. As the alkali, sodium hydroxide, potassium hydroxide, lithium hydroxide, or the like can be used, and lithium hydroxide is used in this embodiment.

In the second pH adjustment step S5, the method for adjusting the pH of the liquid to be treated is not particularly limited, and a commonly used method can be used. For example, by adding an alkaline aqueous solution such as an aqueous lithium hydroxide solution while stirring the liquid to be treated in the second pH adjustment tank 3, the valuable metal in the liquid to be treated is changed to a hydroxide (for example, iron hydroxide, cobalt hydroxide, Furthermore, it precipitates and precipitates as crystals of an inorganic salt such as nickel hydroxide). As a result, cobalt in the liquid to be treated can be recovered as a cobalt salt such as cobalt hydroxide. Although the alkali concentration of the aqueous alkali solution added in the second pH adjustment step S5 is not particularly limited, it is preferably equal to or higher than the alkali concentration of the aqueous alkali solution used in the first pH adjustment step S3.

The precipitate deposited and precipitated in the second pH step S5 is separated from the liquid to be treated by filtering the liquid to be treated in the next solid-liquid separation step S6. In addition, manganese etc. may be contained in the valuable metal removed from the to-be-processed liquid by 2nd pH adjustment process S5. On the other hand, the liquid to be treated (filtrate) after the solid-liquid separation step S6 contains lithium and inorganic acid anions (for example, sulfate ions).

In the solid-liquid separation step S6, it is preferable to wash the precipitate with a washing liquid, and to circulate the washed waste liquid together with the liquid to be treated (filtrate) to the next concentration step S7. As a result, the lithium contained in the washing waste liquid can also be supplied to the concentration step S7 together with the lithium contained in the filtrate, and by carbonating in the carbonation step S8 described later, lithium can be recovered at a high recovery rate. can. The water used for washing the precipitate is not particularly limited, but it is preferable to use the condensed water generated when the liquid to be treated is evaporated and concentrated in the concentration step S7. Available.

In addition, in the first pH adjustment step S3 and the second pH adjustment step S5, by using lithium hydroxide as the alkali to be used, compared to the case of using other alkali metal hydroxide such as sodium hydroxide, For the lithium carbonate crystals deposited in the carbonation step S8, it is possible to suppress contamination of alkali metals other than lithium, such as sodium. Therefore, lithium carbonate with high purity can be recovered.

In the next concentration step S7, the liquid to be treated containing lithium after the solid-liquid separation step S6 is evaporated and concentrated. As a result, the amount of the liquid to be treated decreases and the concentration of lithium in the liquid to be treated increases. Therefore, the recovery rate of lithium carbonate can be improved in the carbonation step S8, which will be described later.

Further, in the concentration step S7, by evaporating and concentrating the liquid to be treated, the temperature of the liquid to be treated after concentration can be increased, and the recovery rate of lithium carbonate can be improved in the carbonation step S8 described later. . The higher the temperature, the lower the solubility of lithium carbonate. Therefore, in the carbonation step S8, the higher the temperature of the liquid to be treated, the lower the solubility of lithium carbonate produced by the reaction between lithium and carbon dioxide gas in the liquid to be treated. Therefore, the amount of lithium carbonate crystals deposited can be increased.

In this concentration step S7, it is preferable to concentrate the liquid to be processed to a concentration such that lithium does not precipitate as crystals of a lithium salt such as lithium sulfate in the liquid to be processed after concentration. As a result, the concentration of lithium in the liquid to be treated after concentration can be increased, and the recovery rate of lithium carbonate in the carbonation step S8, which will be described later, can be improved. In addition, when a deposit precipitates in concentration process S7, you may perform the solid-liquid separation process which isolate|separates this from a to-be-processed liquid.

In the concentration step S7, the method of evaporating and concentrating the liquid to be treated is not particularly limited, and for example, the evaporative concentration device 4 can be used. The evaporative concentration device 4 is not particularly limited as long as it can concentrate the liquid to be treated by evaporation. A heat pump type evaporative concentration apparatus is preferred. When a heat pump type evaporative concentration device is used, the energy used can be significantly suppressed. Energy can be further saved by concentrating the liquid to be treated under a reduced pressure atmosphere.

In the subsequent carbonation step S8, the liquid to be treated after the concentration step S7 is mixed with carbon dioxide gas and/or a water-soluble carbonate is added to precipitate lithium in the liquid to be treated as lithium carbonate crystals. precipitate. Thereby, lithium in the liquid to be treated can be recovered as lithium carbonate. Examples of carbonates that can be used include sodium carbonate, ammonium carbonate, and potassium carbonate.

In the carbonation step S8, it is preferable to deposit and precipitate crystals of lithium carbonate by mixing carbon dioxide gas with the liquid to be treated. In this manner, by using a material that does not contain an alkali metal such as sodium in the carbonation step S8, it is possible to suppress contamination of the precipitated lithium carbonate crystals with an alkali metal other than lithium. Therefore, lithium carbonate with high purity can be recovered.

In the carbonation step S8, the method of mixing carbon dioxide gas with the liquid to be treated is not particularly limited, and a commonly used method can be used. For example, carbon dioxide gas can be uniformly mixed with the liquid to be treated by supplying carbon dioxide gas to the liquid to be treated in the form of fine bubbles through a nozzle while stirring the liquid to be treated in the carbonation tank 5. Lithium and carbon dioxide in the liquid to be treated can be efficiently reacted. Alternatively, the liquid to be treated may be reacted with the carbon dioxide gas by spraying it in an atmosphere of the carbon dioxide gas.

Since the solubility of lithium carbonate decreases as the temperature increases, it is preferable to heat the liquid to be treated in the carbonation step S8. As a result, the solubility of lithium carbonate generated by the reaction between lithium and carbon dioxide gas in the liquid to be treated is lowered, so that the amount of lithium carbonate crystals deposited can be increased.

In the next solid-liquid separation step S9, the liquid to be treated after the carbonation step S8 is filtered to separate precipitates containing crystals of lithium carbonate from the liquid to be treated. In the solid-liquid separation step S9, the precipitate separated from the liquid to be treated is washed with water or the like to remove impurities and increase the purity of lithium carbonate. The water used for washing the precipitate is not particularly limited, but it is preferable to use the condensed water generated when the liquid to be treated is evaporated and concentrated in the concentration step S7. Available. The washing waste liquid after washing the precipitates is preferably supplied to the bipolar membrane electrodialyzer 6 in the electrodialysis step S10, which will be described later, together with the liquid to be treated (filtrate) after the solid-liquid separation step S9.

In the next electrodialysis step S10, the liquid to be treated after the solid-liquid separation step S9 is supplied to the bipolar membrane electrodialyzer 6 to separate and recover the alkali and inorganic acid from the liquid to be treated. As the bipolar membrane electrodialysis device 6, for example, as shown in FIG. A three-chamber cell type bipolar membrane electrodialysis apparatus in which a plurality of are stacked can be preferably used. In the bipolar membrane electrodialyzer 6 of this embodiment, an anion exchange membrane 61 and a cation exchange membrane 62 form a demineralization chamber R1, and an acid chamber R2 is formed between the anion exchange membrane 61 and one bipolar membrane 63. and an alkali chamber R3 is formed between the cation exchange membrane 62 and the bipolar membrane 64 on the other side. An anode chamber R4 and a cathode chamber R5 are formed outside each of the bipolar films 63 and 64, and an anode 65 is disposed in the anode chamber R4 and a cathode 66 is disposed in the cathode chamber R5.

In this electrodialysis step S10, the liquid to be treated is introduced into the demineralization chamber R1, and pure water is introduced into the acid chamber R2 and the alkali chamber R3, respectively, so that the liquid to be treated is lithium and anions of inorganic acid (this embodiment in the form of sulfate ions), lithium ions (Li ⁺ ) pass through the cation exchange membrane 62 and sulfate ions (SO ₄ ²⁻ ) pass through the anion exchange membrane 61 in the demineralization compartment R1. . On the other hand, in the acid chamber R2 and the alkali chamber R3, the supplied pure water is dissociated into hydrogen ions (H ⁺ ) and hydroxide ions (OH ⁻ ) in the bipolar membranes 63 and 64, and in the acid chamber R2 H ⁺ ) combine with sulfate ions (SO ₄ ²⁻ ) to produce sulfuric acid (H ₂ SO ₄ ), and in the alkaline chamber R3, hydroxide ions (OH ⁻ ) combine with lithium ions (Li ⁺ ). Lithium hydroxide (LiOH) is produced. As a result, sulfuric acid (H ₂ SO ₄ ) as an inorganic acid is recovered from the acid chamber R2, and lithium hydroxide (LiOH) as an alkali is recovered from the alkali chamber R3. The pure water introduced into the acid chamber R2 and the alkali chamber R3 may be condensed water generated when the liquid to be treated is evaporated and concentrated in the concentration step S8.

The desalted dilute liquid to be treated (demineralized liquid) discharged from the demineralization chamber R1 is not particularly limited, but at least part of it is supplied to the evaporative concentration device 4, and is concentrated in the concentration step S7. It is preferred to evaporate again.

In addition, the inorganic acid (sulfuric acid in this embodiment) recovered from the acid chamber R2 is not particularly limited, but is supplied to the acid elution tank 1, and the inorganic acid that leaches the waste lithium ion batteries in the acid elution step S1 is used. It is preferred to recycle as an acid.

Further, the alkali (lithium hydroxide in this embodiment) recovered from the alkali chamber R3 is not particularly limited, but is supplied to the pH adjustment tanks 2 and 3, and the liquid to be treated in the pH adjustment steps S3 and S5. It is preferable to reuse as an alkali for pH adjustment of.

According to the method for recovering cobalt of the present embodiment described above, when the impurity metal is removed from the liquid to be treated in the first pH adjustment step S3 in which the cobalt and the impurity metal are dissolved, the alkali concentration is adjusted to 1.5. By adjusting the pH of the liquid to be treated with a dilute alkaline aqueous solution of less than 0 mol/L, it is possible to suppress removal of cobalt together with impurity metals from the liquid to be treated. Therefore, the amount of cobalt in the liquid to be treated supplied to the second pH adjustment step S5 can be maintained high, so that cobalt can be recovered at a high recovery rate in the second pH adjustment step S5.

In addition, according to the cobalt recovery method of the present embodiment, since a dilute alkaline aqueous solution having an alkali concentration of less than 1.0 mol/L is used in the first pH adjustment step S3, carbonic acid is used to recover lithium thereafter. Although the amount of the liquid to be treated supplied to the carbonization step S8 is large, the amount of the liquid to be treated is reduced by evaporating and concentrating the liquid to be treated in the concentration step S7 prior to the carbonation step S8. It increases the lithium concentration in the liquid. Therefore, the recovery rate of lithium carbonate can be favorably improved in the carbonation step S8. Moreover, since the temperature of the liquid to be treated supplied to the carbonation step S8 increases as the liquid to be treated evaporates and concentrates, the solubility of lithium carbonate decreases and the amount of lithium carbonate deposited can be increased.

When adjusting the pH of the liquid to be treated to 4 to 6 in the first pH adjustment step S3, an aqueous alkali solution having an alkali concentration of 1.0 mol/L or more is applied until the pH of the liquid to be treated reaches a predetermined value. After the pH of the liquid to be treated reaches a predetermined value by adding to the liquid to be treated, an alkaline aqueous solution having an alkali concentration of less than 1.0 mol/L is added to the liquid to be treated, thereby adjusting the pH. You can reduce the amount.

Further, according to the cobalt recovery method of the present embodiment, the inorganic acid and alkali recovered in the electrodialysis step S10 are circulated to the acid elution step S1 and the pH adjustment steps S3 and S5, respectively, for reuse. The amounts of inorganic acids and alkalis used in S1, S3 and S5 can be reduced.

Although one embodiment of the cobalt recovery method of the present invention has been described above, the present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the gist of the present invention.

For example, in the cobalt recovery method of the above embodiment, the alkali recovered in the electrodialysis step S10 is supplied to the first pH adjustment step S3 and the second pH adjustment step S5. good too.

In addition, in the cobalt recovery method of the above embodiment, at least part of the dilute liquid to be treated (demineralized liquid) after lithium hydroxide has been recovered in the electrodialysis step S10 is supplied to the concentration step S7. Alternatively or additionally, it may be configured to supply to the electrodialysis step S10.

Moreover, although the cobalt recovery method of the above embodiment includes the concentration step S7 before the carbonation step S8, the concentration step S7 does not necessarily have to be included. In this case, at least part of the dilute liquid to be treated (demineralized liquid) from which lithium hydroxide has been recovered in the electrodialysis step S10 can be configured to be supplied to the carbonation step S8.

Further, in the cobalt recovery method of the above-described embodiment, polyvalent cations having a valence of 2 or higher (typically, calcium ions and magnesium ions) are added to the liquid to be treated which is supplied to the electrodialysis step S10. may be configured to remove impurities of When polyvalent cations such as calcium ions and magnesium ions are present in the liquid to be treated, these polyvalent cations are precipitated in the cation exchange membrane of the bipolar membrane electrodialyzer 6, thereby reducing the performance of the membrane. Although there is a risk of causing this, by removing polyvalent cations from the liquid to be treated in advance, it is possible to prevent adverse effects on the cation exchange membranes in the bipolar membrane electrodialyzer 6 . The specific configuration for removing polyvalent cations is not particularly limited, and for example, a known polyvalent cation removal device capable of passing a liquid to be treated through a column filled with a chelating resin can be exemplified. can be done. As the chelate resin, those capable of selectively capturing calcium ions and magnesium ions can be used, and examples thereof include iminodiacetic acid type and aminophosphate type. Other polyvalent cation removers include those to which a chelating agent is added and those using ion exchange resins. Impurities to be removed from the liquid to be treated may contain silica (silicate ions) in addition to calcium and magnesium.

In addition, as shown in FIGS. 4 and 5, the cobalt recovery method of the above embodiment may further include a roasting step S0 for roasting the waste lithium ion batteries before the acid elution step S1. In the roasting step S0, the method of roasting the waste lithium ion batteries is not particularly limited, and a known roasting equipment 7 can be used. In this embodiment, exhaust gas generated in the roasting equipment 7 (roasting step S0) is supplied to the carbonation tank 6 (carbonation step S8) and mixed with the liquid to be treated as carbon dioxide gas. Thereby, the amount of carbon dioxide used in the carbonation step S8 can be reduced.

In the method for recovering cobalt according to the above embodiment, the method for recovering lithium in the steps subsequent to the concentration step S7 is not particularly limited, and may be, for example, the methods shown in FIGS. In the embodiments of FIGS. 6 and 7, regarding the procedure from the acid elution step S1 to the solid-liquid separation step S6 regarding the cobalt recovery method, the alkali added in the first pH adjustment step S3 and the second pH adjustment step S5 is Since it is the same as the above embodiment except that sodium hydroxide is used instead of lithium hydroxide, detailed description is omitted here.

6 and 7, in the lithium-containing liquid (filtrate) after the solid-liquid separation step S6, in addition to lithium, the inorganic acid added in the acid elution step S1 and the pH adjustment steps S3 and S5 (this in the form of sulfuric acid) and an alkali (sodium hydroxide in this embodiment), in the case where an inorganic salt (sodium sulfate (Na ₂ SO ₄ ) in this embodiment) is dissolved, the inorganic salt is dissolved before the carbonation step S11. It is characterized in that it is removed from the liquid to be treated.

Specifically, in the impurity removal step S7 after the solid-liquid separation step S6, at least calcium and/or magnesium contained in the liquid to be treated after the solid-liquid separation step S6 is removed. By removing calcium and magnesium contained as impurities in the liquid to be treated, it is possible to suppress the generation and adhesion of scale to the heat transfer surface of the heat exchanger of the evaporative concentration device 5 in the concentration step S8 described later. It is possible to maintain high heat exchange efficiency. Further, if calcium or magnesium is contained in the liquid to be treated, polyvalent cations of calcium or magnesium contained in the inorganic solution are transferred to the cation exchange membrane of the bipolar membrane electrodialyzer 9 in the electrodialysis step S14 described later. There is a possibility that it will precipitate inside and cause a deterioration in the performance of the film. Therefore, by removing calcium and magnesium from the liquid to be treated in advance, it is possible to prevent adverse effects on the cation exchange membranes of the bipolar membrane electrodialyzer 9 and maintain high electrodialysis performance.

In the impurity removing step S7, the method for removing calcium and magnesium from the liquid to be treated is not particularly limited, and the polyvalent cation removing device 4 as described above can be used. The impurities removed from the liquid to be treated in the impurity removing step S7 may contain silica (silicate ions) in addition to calcium and magnesium.

In the next concentration step S8, the liquid to be treated after the impurity removal step S7 is evaporated and concentrated. As a result, the amount of the liquid to be treated decreases, and the concentration of lithium in the liquid to be treated increases. Therefore, the recovery rate of lithium carbonate can be improved in the carbonation step S12, which will be described later.

In this concentration step S8, it is preferable to concentrate the liquid to be processed to a concentration such that lithium does not precipitate as crystals of a lithium salt such as lithium sulfate in the liquid to be processed after concentration. As a result, the concentration of lithium in the liquid to be treated after concentration can be increased, and the recovery rate of lithium carbonate in the carbonation step S11, which will be described later, can be improved.

In the concentration step S8, the method of evaporating and concentrating the liquid to be treated is not particularly limited, and for example, the evaporative concentration device 5 can be used. Since the evaporative concentration device 5 is similar to that of the above embodiment, detailed description thereof is omitted here.

In the next crystallization step S9, the liquid to be treated after the concentration step S8 is cooled and crystallized. In the crystallization step S9, the temperature of the liquid to be treated after evaporative concentration is lowered to lower the solubility until the inorganic salt contained in the liquid to be treated is crystallized. In embodiments, the concentration of sodium sulfate) can be reduced. Therefore, the purity of lithium carbonate can be increased when recovering lithium carbonate in the carbonation step S11, which will be described later.

In the crystallization step S9, the method of cooling and crystallizing the liquid to be treated is not particularly limited, and for example, the cooling crystallizer 6 can be used. The cooling crystallizer 6 cools the supplied liquid to be treated in the crystallization tank to precipitate crystals of the desired inorganic salt. As the cooling crystallizer 6, for example, a known cooling crystallizer such as a cooling type crystallizer using a jacket or an internal coil, or an external circulation cooling type crystallizer can be used, and is not particularly limited.

In the crystallization step S9, only crystals of the target inorganic salt are precipitated by utilizing the fact that the saturation solubility and the temperature dependence of the solubility differ depending on the inorganic salt. This embodiment utilizes the fact that temperature dependence of the solubility of lithium salts such as lithium sulfate is smaller than that of inorganic salts other than lithium salts such as sodium sulfate. That is, the inorganic salt other than the lithium salt is precipitated as crystals by cooling to a temperature equal to or higher than the precipitation temperature of the lithium salt at the supply concentration and equal to or lower than the precipitation temperature of the inorganic salt other than the lithium salt. Specifically, the cooling temperature for precipitating sodium sulfate crystals is 30°C or lower, preferably 5°C or higher and 20°C or lower. _At this time, sodium sulfate precipitates in the form of sodium sulfate decahydrate _{( Na2SO4.10H2O} ).

In the next solid-liquid separation step S10, the liquid to be treated after the crystallization step S9 is filtered to separate precipitates containing crystals of an inorganic salt (sodium sulfate in this embodiment) from the liquid to be treated.

In the subsequent carbonation step S11, carbon dioxide gas is mixed with the liquid to be treated and/or a water-soluble carbonate is added to the liquid to be treated from which the precipitates containing crystals of the inorganic salt have been separated. Lithium inside precipitates and precipitates as lithium carbonate crystals. Thereby, lithium in the liquid to be treated can be recovered as lithium carbonate. Examples of carbonates that can be used include sodium carbonate, ammonium carbonate, and potassium carbonate.

In the carbonation step S11, it is preferable to deposit and precipitate crystals of lithium carbonate by mixing carbon dioxide gas with the liquid to be treated. In this manner, by using a material that does not contain an alkali metal such as sodium in the carbonation step S11, it is possible to suppress contamination of the precipitated lithium carbonate crystals with an alkali metal other than lithium. Therefore, lithium carbonate with high purity can be recovered.

However, if the mixing of carbon dioxide gas is continued, the pH of the liquid to be treated decreases, so the amount of lithium carbonate precipitated may decrease. Therefore, it is preferable to stop mixing the carbon dioxide gas before the pH of the liquid to be treated becomes 7 or less. Further, the pH may be prevented from lowering by adding an alkali to the liquid to be treated. In that case, it is preferable to maintain the pH at 9 or more by adding an alkali. As the alkali to be added, sodium hydroxide, potassium hydroxide, lithium hydroxide, or the like can be used.

In the carbonation step S11, the method of mixing carbon dioxide gas with the liquid to be treated is not particularly limited, and a commonly used method can be used as in the above embodiment.

Since the solubility of lithium carbonate decreases as the temperature increases, it is preferable to heat the liquid to be treated in the carbonation step S11. As a result, the solubility of lithium carbonate generated by the reaction between lithium and carbon dioxide gas in the liquid to be treated is lowered, so that the amount of lithium carbonate crystals deposited can be increased. Further, by heating the liquid to be treated, the solubility of the inorganic salt (sodium sulfate in this embodiment) remaining in the liquid to be treated increases, and crystallization of the inorganic salt can be suppressed. Therefore, it is possible to suppress the precipitation of the crystals of the inorganic salt together with the crystals of the lithium carbonate, so that the purity of the lithium carbonate can be increased when recovering the lithium carbonate in the carbonation step.

In the next solid-liquid separation step S12, the liquid to be treated after the carbonation step S11 is filtered to separate precipitates containing crystals of lithium carbonate from the lithium-containing liquid. In the solid-liquid separation step S12, the precipitate separated from the lithium-containing liquid is washed with water or the like to remove impurities and increase the purity of lithium carbonate. The water used for washing the precipitate is not particularly limited, but it is preferable to use the condensed water generated when the liquid to be treated is evaporated and concentrated in the concentration step S8. Available.

The liquid to be treated (filtrate) after the solid-liquid separation step S12 is not particularly limited, but because it contains impurities, part of it is discharged as a blow liquid, but part of it is reintroduced into the system. Circulation is preferred. As a result, lithium remaining in the liquid to be treated can be recovered, so that lithium can be recovered at a high recovery rate. It is preferable that the washing waste liquid after washing the precipitate containing the crystals of lithium carbonate is also circulated again in the system together with the liquid to be treated after the solid-liquid separation step S12.

When the liquid to be treated after the solid-liquid separation step S12 is circulated in the system again, it may be supplied to the evaporative concentration device 5 and evaporated and concentrated in the concentration step S8, but preferably, the first pH adjustment tank 2 and / Or supplied to the second pH adjustment tank 3 . Since the liquid to be treated after the solid-liquid separation step S12 is alkaline, it can be used as an alkali to be added in the pH adjustment steps S3 and S5. Furthermore, if the liquid to be treated after the solid-liquid separation step S12 contains a large amount of carbonate ions (CO ₃ ² − ), the heat transfer of the heat exchanger of the evaporative concentration device 5 during evaporation and concentration in the concentration step S8 Carbonate crystals precipitate on the surface. Therefore, since the filtrate after the solid-liquid separation steps S2 and S4 is acidic, the liquid to be treated after the solid-liquid separation step S12 is neutralized with the filtrate to convert carbonate ions into carbon dioxide gas from the liquid to be treated. By extracting, it is possible to prevent carbonate crystals from depositing on the heat transfer surface of the heat exchanger of the evaporative concentration device 5 in the concentration step S8.

On the other hand, the crystals of the inorganic salt (sodium sulfate in this embodiment) contained in the precipitate separated from the liquid to be treated in the solid-liquid separation step S10 (cooling crystallizer 6) are dissolved in the dissolution step S13 (dissolution tank 8). supplied to In the dissolving step S13, the inorganic salt crystals are dissolved in the dissolving tank 8 to a desired concentration using, for example, water to produce an inorganic salt solution. The temperature at this time is not particularly limited as long as it can dissolve the crystals of the inorganic salt. The water used for dissolving the inorganic salt is not particularly limited, but it is preferable to use the condensed water generated when the liquid to be treated is evaporated and concentrated in the concentration step S8. Effective use is possible. The produced inorganic salt solution is supplied to the bipolar membrane electrodialyzer 9 .

In the next electrodialysis step S14, the bipolar membrane electrodialysis device 9 separates and recovers the alkali and the inorganic acid from the inorganic salt solution after the dissolving step S13. The bipolar membrane electrodialyzer 9 is the same as in the above embodiment, and detailed description is omitted here.

In this electrodialysis step S14, an inorganic salt solution is introduced into the demineralization chamber R1, and pure water is introduced into each of the acid chamber R2 and the alkali chamber R3. As a result, when the inorganic salt solution contains, for example, sodium sulfate, sodium ions (Na ⁺ ) pass through the cation exchange membrane 92 in the demineralization chamber R1 as shown in FIG. (SO ₄ ²⁻ ) passes through the anion exchange membrane 91 . On the other hand, in the acid chamber R2 and the alkali chamber R3, the supplied pure water is dissociated into hydrogen ions (H ⁺ ) and hydroxide ions (OH ⁻ ) in the bipolar membranes 93 and 94, and in the acid chamber R2 H ⁺ ) combine with sulfate ions (SO ₄ ²⁻ ) to produce sulfuric acid (H ₂ SO ₄ ), and in the alkaline chamber R3, hydroxide ions (OH ⁻ ) combine with sodium ions (Na ⁺ ). Sodium hydroxide (NaOH) is produced. As a result, sulfuric acid (H ₂ SO ₄ ) as an inorganic acid is recovered from the acid chamber R2, and sodium hydroxide (NaOH) as an alkali is recovered from the alkali chamber R3.

The desalted dilute inorganic salt solution (desalted solution) discharged from the desalting chamber R1 is not particularly limited, but contains a small amount of lithium, so it is supplied to the evaporative concentration device 5. , it is preferable to evaporate and concentrate again in the concentration step S8.

In addition, the inorganic acid (sulfuric acid in this embodiment) recovered from the acid chamber R2 is not particularly limited, but is supplied to the acid elution tank 1, and the inorganic acid that leaches the waste lithium ion batteries in the acid elution step S1 is used. It is preferred to recycle as an acid. Furthermore, it is preferable to supply the polyvalent cation removal device 4 and reuse it as a regeneration liquid for the chelate resin or ion exchange resin used in the impurity treatment step S7.

In addition, the alkali (sodium hydroxide in this embodiment) recovered from the alkali chamber R3 is not particularly limited, but is supplied to the pH adjustment tanks 2 and 3 and used in the pH adjustment steps S3 and S5 for the lithium-containing liquid. It is preferable to reuse as an alkali for pH adjustment of. Furthermore, it is preferable to supply the polyvalent cation removal device 4 and reuse it as a regeneration liquid for the chelate resin or ion exchange resin used in the impurity treatment step S7.

According to the embodiments of FIGS. 6 and 7, by evaporating and concentrating the liquid to be treated in the concentration step S8 before the carbonation step S11, the amount of the liquid to be treated is reduced and the concentration of lithium in the liquid to be treated is increased. I am letting Therefore, the recovery rate of lithium carbonate crystals can be favorably improved in the carbonation step S11.

Further, in the crystallization step S9 after the concentration step S8, the liquid to be treated is cooled and crystallized to lower the temperature of the liquid to be treated after evaporative concentration, thereby reducing the inorganic salt contained in the liquid to be treated (this embodiment). Sodium sulfate) is reduced in solubility until it crystallizes, so the concentration of the inorganic salt in the liquid to be treated can be reduced. Moreover, in the carbonation step S11, the temperature of the liquid to be treated is raised for the purpose of lowering the solubility of lithium carbonate, so that the solubility of the inorganic salt remaining in the liquid to be treated increases, and crystallization of the inorganic salt can be suppressed. . Therefore, when recovering lithium carbonate in the carbonation step S11, the purity of lithium carbonate can be increased.

Further, according to the embodiments of FIGS. 6 and 7, lithium remaining in the liquid to be treated is circulated in the system without discarding the liquid to be treated after recovering the lithium carbonate crystals in the carbonation step S11. are collected. Therefore, lithium can be recovered at a high recovery rate.

Further, according to the embodiments of FIGS. 6 and 7, the crystals of the inorganic salt (sodium sulfate in this embodiment) contained in the precipitate separated from the liquid to be treated in the solid-liquid separation step S10 are dissolved in the dissolution step S13. After obtaining an inorganic salt solution, the inorganic salt solution is subjected to bipolar membrane electrodialysis in the electrodialysis step S14 to recover the inorganic acid and alkali from the inorganic salt solution, and the dilute inorganic salt solution after desalting is concentrated in the concentration step S8. After evaporating and concentrating, lithium contained in the dilute inorganic salt solution is recovered in the carbonation step S11. Therefore, lithium can be recovered at a high recovery rate. Furthermore, by circulating and reusing the inorganic acid and alkali recovered in the electrodialysis step S14 in the acid elution step S1, pH adjustment steps S3 and S5, and impurity removal step S7, each step S1, S3, S5, and S7 can reduce the amount of inorganic acid or alkali used in

Further, according to the embodiments of FIGS. 6 and 7, calcium and magnesium contained in the liquid to be treated are removed in the impurity removing step S7. As a result, the amount of impurities in the filtrate obtained in the solid-liquid separation step S12 after the carbonation step S11 is reduced, so that most of the liquid to be treated after the solid-liquid separation step S12 can be circulated into the system again. can. Therefore, since more lithium remaining in the liquid to be treated after the solid-liquid separation step S12 can be recovered, lithium can be recovered at a high recovery rate. Furthermore, since the amount of impurities in the inorganic solution electrodialyzed in the electrodialysis step S14 is also reduced, it is possible to prevent the cation exchange membrane of the bipolar electrodialysis device 9 from being destroyed, and maintain high performance of the bipolar membrane. can be done.

Further, according to the embodiments of FIGS. 6 and 7, the condensed water generated in the concentration step S8 is used for various treatments, so the condensed water can be effectively used. Furthermore, by washing the crystals obtained in the solid-liquid separation steps S4, S6, S10, and S12 using condensed water, the recovery rate of each crystal can be improved.

In the embodiments of FIGS. 6 and 7, the impurity removal step S7 is performed to remove at least calcium and/or magnesium from the liquid to be treated before the concentration step S8. Similarly, the inorganic salt solution before the electrodialysis step S14 may be subjected to an impurity removal step for removing at least calcium and/or magnesium.

Further, in the embodiments of FIGS. 6 and 7, the alkali recovered in the electrodialysis step S14 is supplied to the first pH adjustment step S3 and the second pH adjustment step S5. may

6 and 7, as shown in FIGS. 9 and 10, after the dissolving step S13 and before the electrodialysis step S14, a Processing steps may be performed. This treatment step can be performed instead of the impurity removal step S7 or in addition to the impurity removal step S7.

Specifically, first, the inorganic salt (in this embodiment, sodium sulfate) contained in the inorganic salt solution is recrystallized in the recrystallization step S13-1. The method for recrystallizing the inorganic salt contained in the inorganic salt solution is not particularly limited. For example, cooling crystallization by a cooling crystallizer 10 similar to the cooling crystallizer 6 in the crystallization step S9 described above is used. be able to. In other words, it is possible to precipitate only inorganic salt crystals by utilizing the fact that inorganic salts and silica have different saturation solubility and temperature dependence of solubility. Crystals of the inorganic salt are precipitated by cooling below the temperature. _At this time, sodium sulfate precipitates in the form of sodium sulfate decahydrate _{( Na2SO4.10H2O} ). In addition, the inorganic salt solution may be concentrated in advance to an inorganic salt concentration suitable for crystallization of the inorganic salt. In the present embodiment, the cooling crystallizer 10 is used in the recrystallization step S13-1, but any crystallization method that deposits crystals with high purity may be used. For example, an evaporative crystallizer or the like may be used. can.

After reprecipitating the inorganic salt crystals, the inorganic salt crystals are separated from the aqueous solution containing the inorganic salt crystals in the solid-liquid separation step S13-2, and the recrystallized inorganic salt crystals are recovered. As a method for solid-liquid separation, for example, known devices such as various filtration devices such as pressure filtration (filter press), vacuum filtration, and centrifugal filtration, and centrifugal separators such as a decanter type can be used.

Then, in the re-dissolving step S13-3, the collected inorganic salt crystals are dissolved in the re-dissolving tank 11 to a desired concentration using, for example, water to generate an inorganic salt solution again. The temperature at this time is not particularly limited as long as it can dissolve the crystals of the inorganic salt. The water used for dissolving the inorganic salt is not particularly limited, but it is preferable to use the condensed water generated when the liquid to be treated is evaporated and concentrated in the concentration step S8. Effective use is possible. The regenerated inorganic salt solution is supplied to the bipolar membrane electrodialyzer 9 . The impurities removed from the inorganic salt solution in the recrystallization step S13-1 to the redissolving step S13-3 may contain calcium and/or magnesium in addition to silica.

In the embodiments of FIGS. 9 and 10, silica contained in the inorganic salt solution is removed before the electrodialysis step S14. As a result, the amount of impurities in the inorganic solution to be electrodialyzed in the electrodialysis step S14 is also reduced, so that high performance of the bipolar membrane can be maintained. Furthermore, when the dilute inorganic salt solution (demineralized liquid) after the electrodialysis step S14 is supplied to the evaporative concentration device 5 and evaporatively concentrated again in the concentration step S8, the amount of impurities in the demineralized liquid is reduced. , in the concentration step S8, the generation and adhesion of scale to the heat transfer surface of the heat exchanger of the evaporative concentration device 5 can be suppressed. In addition, since the amount of impurities in the filtrate obtained in the solid-liquid separation step S12 after the carbonation step S11 is reduced, most of the liquid to be treated after the solid-liquid separation step S12 can be circulated into the system again. . Therefore, since more lithium remaining in the liquid to be treated after the solid-liquid separation step S12 can be recovered, lithium can be recovered at a high recovery rate.

6 and 7 and the embodiments of FIGS. 9 and 10, waste lithium ion batteries are removed before the acid elution step S1, as in the embodiments of FIGS. It may further have a roasting step S0 of roasting.

In addition, the cobalt recovery method of the above embodiment exemplifies the case of recovering cobalt from waste lithium ion batteries, but the present invention is not limited to the method used for recovering cobalt from waste lithium ion batteries. .

Examples of the present invention will be described below. In addition, the present invention is not limited to the following examples.

To 200 ml of the liquid to be treated having the components shown in Table 1 below, an aqueous alkali solution was added to adjust the pH of the liquid to be treated (first pH adjustment step). A lithium hydroxide aqueous solution was used as the alkaline aqueous solution to be added. The alkali concentration of the lithium hydroxide aqueous solution was 0.2 mol/L (Example 1), 0.5 mol/L (Example 2), and 1.0 mol/L (Comparative Example), and the pH of the liquid to be treated was 4.0. The amount of the lithium hydroxide aqueous solution added was adjusted so as to obtain 7. The amount of lithium hydroxide aqueous solution added was 418.6 ml in Example 1, 168.5 ml in Example 2, and 86.3 ml in Comparative Example. The addition of the aqueous lithium hydroxide solution further increased the lithium content in the liquid to be treated to 582 mg in Example 1, 585 mg in Example 2, and 599 mg in Comparative Example.

After the pH adjustment, the liquid to be treated was filtered using filter paper, and the content of each component contained in the filtrate obtained by the filtration was measured. Table 2 shows the results.

On the other hand, the surface state of the filtration residue obtained by filtration of the liquid to be treated after pH adjustment was confirmed. The results are shown in FIGS. 11 to 13. FIG. 11 shows Example 1, FIG. 12 shows Example 2, and FIG. 13 shows a comparative example. According to FIG. 13, it was possible to visually confirm that cobalt hydroxide was contained in the filtration residue in the comparative example, but according to FIGS. The inclusion of cobalt could not be visually confirmed.

From the above results, according to FIGS. 11 to 13, when the alkali concentration of the alkaline aqueous solution added to the liquid to be treated in the first pH adjustment step is 1.0 mol/L, the filtration residue after pH adjustment of the liquid to be treated It was confirmed that many cobalt salts were contained in Further, according to Table 2, when the alkali concentration of the alkaline aqueous solution added to the liquid to be treated in the first pH adjustment step is 1.0 mol/L, the cobalt recovery rate of the liquid to be treated (filtrate) after pH adjustment is While it is less than 85%, when the alkali concentration is less than 1.0 mol / L, the cobalt recovery rate of the treated liquid (filtrate) after pH adjustment is 85% or more, and the treated liquid It was confirmed that a large amount of cobalt remained in the (filtrate).

Thus, by setting the alkali concentration of the alkaline aqueous solution added to the liquid to be treated in the first pH adjustment step to less than 1.0 mol/L, cobalt is removed from the liquid to be treated in the first pH adjustment step together with the impurity metal (for example, aluminum). It can be seen that removal of cobalt can be suppressed, and the content of cobalt in the liquid to be treated supplied to the next second pH adjustment step can be maintained at a high level. Therefore, it is possible to recover cobalt at a high recovery rate in the second pH adjustment step.

If the cobalt recovery rate is improved by 1%, for example, the amount of waste lithium ion batteries processed per year is 1000 tons, and if the cobalt content in the waste lithium ion batteries is 20%, the cobalt recovery amount is 1 year. If the unit price of cobalt is 6,000 yen/kg, the difference is 12,000,000 yen per year.

S0 roasting step S1 acid elution step S3 first pH adjustment step S5 second pH adjustment step S7 concentration step S8 carbonation step S10 electrodialysis step

Claims (7)

a first pH adjustment step of adding an aqueous alkali solution to an acidic treatment liquid in which at least cobalt and impurity metals are dissolved to adjust the pH to 4 to 6, thereby precipitating a salt of the impurity metals as crystals;
a first solid-liquid separation step of separating a precipitate containing impurity metal salt crystals precipitated in the first pH adjustment step from the liquid to be treated;
a second pH adjustment step of precipitating a cobalt salt as crystals by adding an alkaline aqueous solution to the liquid to be treated after the first solid-liquid separation step to adjust the pH to 7 to 11;
a second solid-liquid separation step of separating a precipitate containing cobalt salt crystals precipitated in the second pH adjustment step from the liquid to be treated;
The method for recovering cobalt, wherein the aqueous alkali solution added in the first pH adjustment step has an alkali concentration of less than 1.0 mol/L. 2. The method for recovering cobalt according to claim 1, wherein the alkaline aqueous solution added in the first pH adjustment step has an alkali concentration of 0.1 mol/L or more. In the first pH adjustment step, an aqueous alkali solution having an alkali concentration of 1.0 mol/L or more is added to the liquid to be treated until the pH of the liquid to be treated reaches a predetermined value lower than 4, and then 1.0 mol/L. 3. The method for recovering cobalt according to claim 1, wherein an aqueous alkali solution having an alkali concentration of less than L is added to the liquid to be treated to adjust the pH of the liquid to be treated to 4 to 6. Lithium is dissolved in the liquid to be treated,
A concentration step of evaporating and concentrating the liquid to be treated after the second solid-liquid separation step;
4. The cobalt recovery method according to any one of claims 1 to 3, further comprising a carbonation step of mixing carbon dioxide gas and/or adding a water-soluble carbonate to the liquid to be treated after the concentration step. a third solid-liquid separation step of separating a precipitate containing lithium carbonate crystals precipitated in the carbonation step from the liquid to be treated;
an electrodialysis step of separating and recovering alkali from the liquid to be treated by subjecting the liquid to be treated after the third solid-liquid separation step to bipolar membrane electrodialysis;
5. The cobalt recovery method according to claim 4, wherein the alkali recovered in the electrodialysis step is reused as the alkali added in the first pH adjustment step and/or the second pH adjustment step. The method for recovering cobalt according to any one of claims 1 to 5, wherein the aqueous alkali solution added in the first pH adjustment step has an alkali concentration of 0.5 mol/L or less. The cobalt recovery method according to any one of claims 1 to 6, wherein the alkali added in the first pH adjustment step is sodium hydroxide, potassium hydroxide or lithium hydroxide.

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