CN113453788A

CN113453788A - Lithium recovery method

Info

Publication number: CN113453788A
Application number: CN202080015371.0A
Authority: CN
Inventors: 三保庆明; 纪平幸则; 横山佳帆; 石田和彦; 平野悟; 藤原义浩
Original assignee: Sasakura Engineering Co Ltd
Current assignee: Sasakura Engineering Co Ltd
Priority date: 2019-02-20
Filing date: 2020-02-17
Publication date: 2021-09-28
Also published as: KR20210129042A; WO2020171009A1

Abstract

Provided is a lithium recovery method capable of recovering lithium from a liquid to be treated in which lithium and an inorganic salt are dissolved, with high purity. The lithium recovery method comprises the following steps: a concentration step (S8) in which a liquid to be treated in which at least lithium and an inorganic salt are dissolved is evaporated and concentrated; a crystallization step (S9) for cooling and crystallizing the liquid to be treated after the concentration step (S8) to precipitate inorganic salts as crystals; a solid-liquid separation step (S10) for separating a precipitate containing crystals of an inorganic salt from the liquid to be treated after the crystallization step (S9); a carbonation step (S11) of mixing carbon dioxide and/or adding a water-soluble carbonate to the liquid to be treated (S10) after the solid-liquid separation step; and a solid-liquid separation step (S12) for separating a precipitate containing crystals of lithium carbonate precipitated in the carbonation step (S11) from the liquid to be treated.

Description

Lithium recovery method

Technical Field

The present disclosure relates to a lithium recovery method for recovering lithium from a liquid to be treated in which at least lithium is dissolved, and more particularly to a lithium recovery method used when lithium is recovered from a waste lithium ion battery.

The present disclosure also relates to a cobalt recovery method for recovering cobalt from a treatment target solution in which at least cobalt and an impurity metal are dissolved, and particularly relates to a cobalt recovery method used in recovering cobalt from a spent lithium ion battery.

Background

Lithium ion batteries have attracted attention as lightweight and high energy density batteries, and are widely used as storage batteries for various portable devices, electric vehicles, electric power-assisted bicycles, and the like. In the positive electrode of the lithium ion battery, for example, a lithium transition metal oxide such as lithium cobaltate or lithium nickelate is used as a positive electrode active material, and cobalt and nickel which are precious metals are recovered from a waste lithium ion battery are very important for effective utilization of resources, and thus various methods have been proposed.

As a method for recovering cobalt from a spent lithium ion battery, for example, patent document 1 describes the following method: leaching the waste lithium ion battery with sulfuric acid to dissolve cobalt, adding alkali into the acid leaching solution to adjust the pH to 4-5, thereby precipitating and precipitating impurity metal salts such as aluminum dissolved together with cobalt in the form of crystals, then adding alkali to adjust the pH to 7-10, thereby precipitating and precipitating cobalt salts in the form of crystals, thereby recovering cobalt.

On the other hand, methods for recovering lithium from waste lithium ion batteries have not proposed much because of the low value of lithium. However, since the demand for lithium ion batteries is increasing and waste is expected to increase in the future, it would be advantageous if lithium could be efficiently recovered.

Patent document 2 describes the following method: the used lithium metal gel and solid polymer electrolyte secondary battery are dissolved with sulfuric acid, lithium hydroxide or ammonium hydroxide is added to the lithium sulfate-containing liquid containing lithium sulfate thus obtained to neutralize, thereby precipitating and separating a salt of an impurity metal (aluminum hydroxide) in the form of crystals, and then carbonation is performed after evaporation concentration of the lithium sulfate-containing liquid, thereby forming and precipitating lithium carbonate crystals from lithium contained in the lithium sulfate-containing liquid, which is separated and recovered.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 5077788

Patent document 2: japanese Kokai publication Hei-2004-508694

Disclosure of Invention

Problems to be solved by the invention

However, in the method described in patent document 2, if ammonium hydroxide is used for neutralization when removing impurities (aluminum hydroxide) from a lithium sulfate-containing liquid, the neutralized lithium sulfate-containing liquid contains ammonium sulfate as an inorganic salt. If carbonation is performed in a state where the lithium sulfate-containing liquid contains an inorganic salt, the concentration of the inorganic salt in the lithium sulfate-containing liquid increases due to concentration, and crystallization may occur. Therefore, the inorganic salt is contained in the lithium carbonate at the time of carbonation, and therefore, there is room for improvement in terms of a decrease in the purity of the recovered lithium carbonate.

In order to solve the above problems, an object of the present disclosure is to provide a lithium recovery method capable of recovering lithium from a liquid to be treated in which lithium and an inorganic salt are dissolved, with high purity.

Means for solving the problems

A lithium recovery method according to an aspect of the present disclosure is characterized by including the steps of: a concentration step of evaporating and concentrating a liquid to be treated in which at least lithium and an inorganic salt are dissolved; a crystallization step of cooling and crystallizing the liquid to be treated after the concentration step to precipitate inorganic salts in the form of crystals; a first solid-liquid separation step of separating a precipitate containing crystals of an inorganic salt from the liquid to be treated after the crystallization step; a carbonation step of mixing carbon dioxide and/or adding a water-soluble carbonate to the liquid to be treated after the first solid-liquid separation step 1; and a 2 nd solid-liquid separation step of separating precipitates containing crystals of lithium carbonate precipitated in the carbonation step from the liquid to be treated.

According to the lithium recovery method of one aspect of the present disclosure, the liquid to be treated is evaporated and concentrated in the concentration step before the carbonation step, thereby reducing the amount of the liquid to be treated and increasing the lithium concentration in the liquid to be treated. This can improve the recovery rate of lithium carbonate in the carbonation step.

Further, the solution to be treated is cooled and crystallized in the crystallization step after the concentration step, whereby the temperature of the solution to be treated after evaporation and concentration is lowered to lower the solubility until the inorganic salt contained in the solution to be treated is crystallized. This can reduce the concentration of inorganic salts in the liquid to be treated. In addition, since the temperature of the treatment target liquid is increased to decrease the solubility of lithium carbonate in the carbonation step, the solubility of the inorganic salt remaining in the treatment target liquid is increased, and the crystallization of the inorganic salt can be suppressed. Thus, when lithium carbonate is recovered in the carbonation step, the purity of lithium carbonate can be improved.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the lithium recovery method of the present disclosure, lithium can be recovered with high purity from a liquid to be treated in which lithium and an inorganic salt are dissolved.

Drawings

Fig. 1 is a flowchart schematically showing the steps of the lithium recovery method according to the first embodiment.

Fig. 2 is a schematic diagram showing a schematic configuration of a processing apparatus used in the lithium recovery method of fig. 1.

Fig. 3 is a schematic diagram showing a schematic configuration of the bipolar membrane electrodialysis device.

Fig. 4 is a flowchart schematically showing steps of a modification of the lithium recovery method according to the first embodiment.

Fig. 5 is a schematic diagram showing a schematic configuration of a processing apparatus used in the lithium recovery method of fig. 4.

Fig. 6 is a flowchart schematically showing steps of a modification of the lithium recovery method according to the first embodiment.

Fig. 7 is a schematic diagram showing a schematic configuration of a processing apparatus used in the lithium recovery method of fig. 6.

Fig. 8 is a flowchart schematically showing the steps of the lithium recovery method according to embodiment 2.

Fig. 9 is a schematic diagram showing a schematic configuration of a processing apparatus used in the lithium recovery method of fig. 8.

Fig. 10 is a schematic diagram showing a schematic configuration of the bipolar membrane electrodialysis device.

Fig. 11 is a flowchart schematically showing steps of a modification of the lithium recovery method according to embodiment 2.

Fig. 12 is a schematic diagram showing a schematic configuration of a processing apparatus used in the lithium recovery method of fig. 11.

Fig. 13 is a flowchart schematically showing steps of a modification of the lithium recovery method according to embodiment 2.

Fig. 14 is a schematic diagram showing a schematic configuration of a processing apparatus used in the lithium recovery method of fig. 13.

Fig. 15 is a flow diagram schematically illustrating the steps of a cobalt recovery process.

Fig. 16 is a schematic diagram showing a schematic configuration of a processing apparatus used in the cobalt recovery method of fig. 15.

Fig. 17 is a schematic diagram showing a schematic configuration of the bipolar membrane electrodialysis device.

Fig. 18 is a flowchart schematically showing steps of a variation of the cobalt recovery method.

Fig. 19 is a schematic diagram showing a schematic configuration of a processing apparatus used in the cobalt recovery method of fig. 18.

FIG. 20 is a photograph showing the surface state of the filtration residue of example 1.

FIG. 21 is a photograph showing the surface state of the filtered residue of example 2.

FIG. 22 is a photograph showing the surface state of the filtration residue of example 3.

Detailed Description

Embodiments of the lithium recovery method of the present disclosure are described below with reference to the drawings. In the following description, "to" means not less than and not more than.

Method for recovering lithium according to embodiment 1

A lithium recovery method according to claim 1 of the present disclosure is characterized by including the steps of: a concentration step of evaporating and concentrating a liquid to be treated in which at least lithium and an inorganic salt are dissolved; a crystallization step of cooling and crystallizing the liquid to be treated after the concentration step to precipitate inorganic salts in the form of crystals; a first solid-liquid separation step of separating a precipitate containing crystals of an inorganic salt from the liquid to be treated after the crystallization step; a carbonation step of mixing carbon dioxide and/or adding a water-soluble carbonate to the liquid to be treated after the first solid-liquid separation step 1; and a 2 nd solid-liquid separation step of separating precipitates containing crystals of lithium carbonate precipitated in the carbonation step from the liquid to be treated.

In the lithium recovery method according to paragraph 0016, it is preferable that at least a part of the liquid to be treated after the 2 nd solid-liquid separation step is concentrated by evaporation in the concentration step.

In addition, the lithium recovery method according to paragraph 0016 or 0017 preferably further includes, before the concentration step, an impurity removal step of removing at least calcium and/or magnesium contained in the liquid to be treated.

Further, the lithium recovery method according to any one of paragraphs 0016 to 0018, preferably further comprises the steps of: a dissolving step of dissolving crystals of an inorganic salt contained in the precipitate separated from the liquid to be treated in the first solid-liquid separation step 1 to produce an inorganic salt solution; and an electrodialysis step of subjecting the inorganic salt solution obtained in the dissolving step to bipolar membrane electrodialysis to separate and recover the inorganic acid from the inorganic salt solution together with the alkali.

In the lithium recovery method according to paragraph 0019, the concentration step preferably includes evaporating and concentrating the inorganic salt solution desalted by the bipolar membrane electrodialysis.

In addition, in the lithium recovery method described in paragraph 0019 or 0020, it is preferable to further include an impurity removal step of removing at least a substance causing troubles such as scaling by starting electrodialysis of calcium and/or magnesium contained in an inorganic salt solution, before the electrodialysis step.

In the lithium recovery method according to any one of paragraphs 0019 to 0021, it is preferable that the method further comprises, before the electrodialysis step, the step of: a recrystallization step of recrystallizing an inorganic salt contained in an inorganic salt solution and separating crystals of the inorganic salt from the inorganic salt solution; and a redissolution step of dissolving crystals of the inorganic salt obtained in the recrystallization step to produce an inorganic salt solution.

In the lithium recovery method according to any one of paragraphs 0019 to 0022, it is preferable that the condensed water generated in the concentration step is used for dissolving the inorganic salt in the dissolution step.

In the lithium recovery method according to any one of paragraphs 0019 to 0022, the inorganic acid recovered in the electrodialysis step is preferably used as a regeneration liquid of a chelate resin or an ion exchange resin used in the impurity treatment step.

In the lithium recovery method according to any one of paragraphs 0016 to 0024, it is preferable that the condensed water generated in the concentration step is used to wash a precipitate containing crystals of an inorganic salt obtained in the 1 st solid-liquid separation step and/or a precipitate containing crystals of lithium carbonate obtained in the 2 nd solid-liquid separation step.

Further, the lithium recovery method according to any one of paragraphs 0016 to 0025, preferably further comprising, before the concentration step, the step of: an acid leaching step of leaching the spent lithium ion battery with an inorganic acid to leach lithium; and a pH adjustment step of adding a base to the lithium-containing liquid obtained in the acid leaching step to adjust the pH, and separating the precipitate precipitated in the pH adjustment step from the lithium-containing liquid to produce a liquid to be treated.

Further, in the lithium recovery method described in paragraph 0026, at least a part of the liquid to be treated after the 2 nd solid-liquid separation step is preferably reused as the alkali added in the pH adjustment step.

Further, in the method for recovering lithium described in paragraph 0026 or 0027, it is preferable that the base recovered in the electrodialysis step is reused as the base added in the pH adjustment step, and the inorganic acid recovered in the electrodialysis step is reused as the inorganic acid used in the acid leaching step.

In the lithium recovery method according to any one of paragraphs 0026 to 0028, it is preferable that the precipitate precipitated in the pH adjustment step is washed with condensed water generated in the concentration step.

In the lithium recovery method according to any one of paragraphs 0026 to 0029, it is preferable that a baking step of baking the spent lithium ion battery is further provided before the acid leaching step, and an exhaust gas generated in the baking step is mixed as carbon dioxide into the liquid to be treated in the carbonation step.

According to the lithium recovery method of claim 1 of the present disclosure, the liquid to be treated is evaporated and concentrated in the concentration step before the carbonation step, thereby reducing the amount of the liquid to be treated and increasing the lithium concentration in the liquid to be treated. This can improve the recovery rate of lithium carbonate in the carbonation step.

Further, the temperature of the liquid to be treated after the evaporation and concentration is lowered by cooling and crystallizing the liquid to be treated in the crystallization step after the concentration step, thereby lowering the solubility until the inorganic salt contained in the liquid to be treated is crystallized. This can reduce the concentration of the inorganic salt in the liquid to be treated. In addition, since the temperature of the treatment target liquid is increased to decrease the solubility of lithium carbonate in the carbonation step, the solubility of the inorganic salt remaining in the treatment target liquid is increased, and the crystallization of the inorganic salt can be suppressed. Thus, when lithium carbonate is recovered in the carbonation step, the purity of lithium carbonate can be improved.

Fig. 1 shows steps of respective steps in an embodiment of a lithium recovery method according to a first embodiment of the present disclosure, and fig. 2 shows a schematic configuration of a processing apparatus 10 for implementing the lithium recovery method of fig. 1. The lithium recovery method according to the present embodiment is suitable for lithium, and can be suitably used for treating a liquid to be treated containing a strong acid such as hydrochloric acid, sulfuric acid, hydrofluoric acid, or phosphoric acid and an inorganic salt of an alkali metal or an alkaline earth metal such as potassium or sodium, and particularly for recovering lithium from a waste lithium ion battery. The following description will be given taking a case of recovering lithium from a waste lithium ion battery as an example.

The lithium recovery method of the present embodiment includes:

an acid leaching step S1 of leaching the spent lithium ion battery with an inorganic acid to leach out lithium;

a solid-liquid separation step S2 of separating insoluble residues from the lithium-containing liquid obtained in the acid leaching step S1;

a pH adjustment step S3 or S5 of adding a base to the lithium-containing liquid after the solid-liquid separation step S2 to adjust the pH;

a solid-liquid separation step S4, S6 for separating precipitates from the lithium-containing liquid after the pH adjustment step S3, S5;

an impurity removal step S7 of performing a chelating treatment on the liquid to be treated obtained by separating precipitates from the lithium-containing liquid after the pH adjustment steps S3 and S5;

a concentration step S8 of evaporating and concentrating the treatment target liquid in which at least lithium and an inorganic salt are dissolved after the impurity removal step S7;

a crystallization step S9 of cooling and crystallizing the liquid to be treated after the concentration step S8 to precipitate inorganic salts as crystals;

a solid-liquid separation step S10 (corresponding to the "1 st solid-liquid separation step" in paragraph 0016) of separating a precipitate containing crystals of an inorganic salt from the liquid to be treated after the crystallization step S9;

a carbonation step S11 of mixing carbon dioxide and/or adding a water-soluble carbonate to the liquid to be treated after the solid-liquid separation step S10; and the combination of (a) and (b),

a solid-liquid separation step S12 (corresponding to the "2 nd solid-liquid separation step" in paragraph 0016) of separating precipitates containing crystals of lithium carbonate precipitated in the carbonation step S11 from the liquid to be treated. The lithium recovery method of the present embodiment further includes:

a dissolving step S13 of dissolving crystals of the inorganic salt contained in the precipitate separated from the liquid to be treated in the solid-liquid separation step S10 to form an inorganic salt solution; and the combination of (a) and (b),

an electrodialysis step S14 of separating and recovering the base and the inorganic acid from the inorganic salt solution after the dissolving step S13 by subjecting the inorganic salt solution to bipolar membrane electrodialysis.

The waste lithium ion battery to be subjected to lithium recovery includes: a used lithium ion battery in which the charge capacity is reduced by using the battery for a predetermined number of times of charge and discharge, a semi-finished product in which a failure or the like occurs in a battery manufacturing process, an old-fashioned stock product accompanying a change in product specifications, and the like. The waste lithium ion battery may be subjected to a pulverization or baking treatment, or may be a powder obtained by the pulverization and baking treatment.

First, in the acid leaching step S1, the spent lithium ion battery is leached with an inorganic acid, whereby lithium and metals such as aluminum, nickel, cobalt, and iron are eluted. As the inorganic acid, for example, sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, or the like can be used, and in the present embodiment, sulfuric acid is used from the viewpoint of low cost and easy handling.

In the acid leaching step S1, the method of leaching the spent lithium ion battery with the inorganic acid is not particularly limited, and a commonly used method can be used. For example, the spent lithium ion battery is immersed in an aqueous solution of an inorganic acid such as an aqueous solution of sulfuric acid and stirred for a predetermined time in the acid leaching tank 1, thereby obtaining a lithium-containing liquid in which the above-described metal such as lithium is dissolved. In the acid leaching step S1, the concentration of the inorganic acid in the aqueous solution is preferably 1mol to 5mol/L, and the temperature of the aqueous solution is preferably 60 ℃ or higher.

In the subsequent solid-liquid separation step S2, the lithium-containing liquid obtained in the acid leaching step S1 is filtered, for example, to separate insoluble residues from the lithium-containing liquid. The insoluble residue is mainly a carbon material, a metal material, or an organic material insoluble in an inorganic acid. As a method for performing solid-liquid separation, for example, various filtration apparatuses such as pressure filtration (filter press), vacuum filtration, and centrifugal filtration, and known solid-liquid separation apparatuses such as centrifugal separation apparatuses of a decanter type can be used. The same applies to the following solid-liquid separation steps S4, S6, S10, S12, and the like.

In the subsequent pH adjustment steps S3 and S5, the lithium-containing liquid (filtrate) after the solid-liquid separation step S2 is added with a base to adjust the pH to a predetermined range, thereby removing metals other than lithium from the metals in the lithium-containing liquid. As the alkali, for example, sodium hydroxide, potassium hydroxide, lithium hydroxide, or the like can be used, and in the present embodiment, sodium hydroxide is used in terms of low cost and easy handling.

The method for adjusting the pH of the lithium-containing liquid in the pH adjustment steps S3 and S5 is not particularly limited, and a commonly performed method can be used. For example, by adding an aqueous solution of a base such as an aqueous sodium hydroxide solution while stirring the lithium-containing liquid in the

pH adjustment tanks

1 and 2 and 3, metals other than lithium in the lithium-containing liquid are precipitated and precipitated in the form of crystals of inorganic salts such as hydroxides. In the present embodiment, the pH adjusting processes S3, S5 are divided into a 1 st pH adjusting process S3 and a 2 nd pH adjusting process S5.

In the pH adjustment step S3, the pH of the lithium-containing liquid is adjusted to 4 to 7, preferably 4 to 6, and more preferably 4 to 5 by adding an alkali. Thereby, the impurity metals (e.g., aluminum and iron) in the lithium-containing liquid are precipitated and precipitated in the form of crystals of inorganic salts such as hydroxides (e.g., aluminum hydroxide and iron hydroxide). In the pH adjustment step S3 of step 1, the temperature of the lithium-containing liquid is preferably raised to a constant temperature of, for example, 30 to 80 ℃.

The aqueous solution of the alkali added in the pH 1 adjustment step S3 is preferably diluted to have an alkali concentration of less than 1.0 mol/L. As a result, although described in detail later, in the pH adjustment step S3 1, the precipitation, and removal of cobalt in the lithium-containing liquid as a cobalt salt together with the impurity metal can be suppressed. However, if the alkali concentration is too low, the lower limit of the alkali concentration is preferably 0.1mol/L or more because it is necessary to use a large amount of an aqueous alkali solution to adjust the pH in the 1 st pH adjustment step S3 and the amount of liquid in the lithium-containing liquid after pH adjustment increases. In addition, in order to effectively suppress the removal of cobalt in the lithium-containing liquid from the lithium-containing liquid in the 1 st pH adjustment step S3, the alkali concentration of the aqueous solution of the alkali added in the 1 st pH adjustment step S3 is preferably 0.5mol/L or less, and more preferably 0.2mol/L or less.

In the 1 st pH adjustment step S3, in order to reduce the amount of the aqueous solution of the alkali used for pH adjustment, 1.0mol/L or more of an aqueous solution of an alkali having a high alkali concentration may be added to the lithium-containing liquid to a predetermined value at which the pH of the lithium-containing liquid is less than 4, and after the pH of the lithium-containing liquid reaches the predetermined value, an aqueous solution of an alkali having a low alkali concentration of less than 1.0mol/L may be added to the lithium-containing liquid, thereby adjusting the pH of the lithium-containing liquid to 4 to 7. The predetermined value of the pH of the lithium-containing liquid may be set within a range of 2 to 3.

The precipitate precipitated in the pH adjustment step S3 in the 1 st pH adjustment step S4 is separated from the lithium-containing liquid by, for example, filtering the lithium-containing liquid. The impurity metals removed from the lithium-containing liquid in the pH adjustment step S3 of step 1 may further include copper or the like. In the solid-liquid separation step S4, it is preferable to wash the precipitate with a cleaning liquid and supply the washed waste washing liquid together with the lithium-containing liquid (filtrate) to the next pH adjustment step S5 of 2. Thus, lithium contained in the waste washing liquid may be supplied from the pH 2 adjustment step S5 to the carbonation step S11 together with lithium contained in the lithium-containing liquid, and the lithium may be recovered at a high recovery rate by performing carbonation in the carbonation step S11 described later. The water used for washing the precipitates is not particularly limited, but is preferably condensed water generated when the liquid to be treated is concentrated by evaporation in the concentration step S8 described later, whereby the condensed water can be effectively used.

In the pH 2 adjustment step S5, a base is added to the lithium-containing liquid (filtrate) after the solid-liquid separation step S4 to adjust the pH to 7 or more, preferably 7 to 13, more preferably 7 to 11, and still more preferably 8 to 10. Thereby, the noble metal (e.g., cobalt and nickel) in the lithium-containing liquid is precipitated and precipitated in the form of crystals of an inorganic salt such as a hydroxide (e.g., cobalt hydroxide and nickel hydroxide). In the 2 nd pH adjustment step S5, the lithium-containing liquid is preferably heated to a constant temperature of, for example, 30 to 80 ℃. The alkali concentration of the aqueous alkali solution to be added in the 2 nd pH adjustment step S5 is not particularly limited, but is preferably equal to or higher than the alkali concentration of the aqueous alkali solution used in the 1 st pH adjustment step S3, and more preferably 0.2mol/L or higher.

The precipitate precipitated and precipitated in the pH 2 adjustment step S5 is separated from the lithium-containing liquid in the subsequent solid-liquid separation step S6 by, for example, filtering the lithium-containing liquid. The noble metal removed from the lithium-containing liquid in the pH adjustment step 2S 5 may further include manganese or the like.

On the other hand, in the lithium-containing liquid (filtrate) after the solid-liquid separation step S6, in addition to lithium, an inorganic salt (in the present embodiment, sodium sulfate (Na) in the present embodiment) is dissolved by an inorganic acid (sulfuric acid in the present embodiment) and a base (sodium hydroxide in the present embodiment) added in the acid leaching step S1 and the pH adjustment steps S3 and S5₂SO₄)). The lithium-containing liquid after the pH adjustment steps S3 and S5 corresponds to the "liquid to be treated" in the lithium recovery method of the present disclosure. At least 1 of calcium, magnesium, and silica may be further dissolved in the liquid to be treated.

In the solid-liquid separation step S6, it is preferable to wash the precipitate with a cleaning liquid and supply the washed waste cleaning liquid together with the liquid to be treated (filtrate) to the next impurity removal step S7. Thus, lithium contained in the waste cleaning liquid can be supplied from the impurity removal step S7 to the carbonation step S11 together with lithium contained in the liquid to be treated, and lithium can be recovered at a high recovery rate by carbonation in the carbonation step S11 described later. The water used for washing the precipitates is not particularly limited, and it is preferable to utilize condensed water generated when the liquid to be treated is concentrated by evaporation in the concentration step S8 described later, whereby the condensed water can be effectively utilized.

In the subsequent impurity removal step S7, at least polyvalent cations such as calcium and/or magnesium contained in the liquid to be treated after the solid-liquid separation step S6 are removed. By removing calcium, magnesium, and the like contained as impurities in the liquid to be treated, generation and adhesion of scale on the heat transfer surface of the heat exchanger of the evaporation and concentration device 5 can be suppressed in the concentration step S8 described later, and the heat exchange efficiency can be maintained high. Further, if the liquid to be treated contains calcium, magnesium, or the like, polyvalent cations such as calcium, magnesium, or the like contained in the inorganic solution are precipitated in the cation exchange membrane of the bipolar membrane electrodialysis device 9 in the electrodialysis step S14 described later, which may cause a decrease in membrane performance. Therefore, by previously performing electrodialysis of calcium, magnesium, or the like to remove substances causing troubles such as scaling from the treatment liquid, it is possible to prevent adverse effects on the cation exchange membrane of the bipolar membrane electrodialysis device 9 and maintain the performance of electrodialysis high.

In the impurity removal step S7, the method for removing calcium and magnesium from the treatment liquid is not particularly limited, and, for example, the polyvalent cation removal device 4 can be used. The polyvalent cation removal device 4 is a device for removing polyvalent cations having a valence of 2 or more, such as calcium ions and magnesium ions, and can be configured, for example, by allowing a treatment solution to be introduced into a column packed with a chelate resin. As the chelate resin, a chelate resin capable of selectively capturing calcium ions and magnesium ions can be used, and examples thereof include iminodiacetic acid type and aminophosphonic acid type. The polyvalent cation removal apparatus 4 may be one to which a chelating agent is added or one using an ion exchange resin. The impurities removed from the treatment liquid in the impurity removal step S7 may include silicon dioxide (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 heated and evaporated, and the liquid to be treated is concentrated by evaporating water in the liquid to be treated. This reduces the amount of liquid in the treatment target liquid and increases the lithium concentration in the treatment target liquid. This can improve the recovery rate of lithium carbonate in the carbonation step S11 described later.

In the concentration step S8, the liquid to be treated is preferably concentrated to a concentration at which lithium is not precipitated in the concentrated liquid to be treated, for example, in the form of crystals of a lithium salt such as lithium sulfate. This can increase the lithium concentration in the concentrated liquid to be treated, and the recovery rate of lithium carbonate can be increased in the carbonation step S11 described later.

In the concentration step S8, the method of evaporating and concentrating the liquid to be treated is not particularly limited, and, for example, the evaporation and concentration apparatus 5 can be used. The evaporation concentration device 5 is not particularly limited as long as it can concentrate the liquid to be treated by evaporation, and known evaporation concentration devices such as a heat pump type, an ejector (injector) type, a steam type, and a flash evaporation type can be used. When the heat pump type evaporation and concentration apparatus is used, the energy used can be significantly suppressed. Further, energy saving can be achieved by concentrating the treatment target liquid under a reduced pressure atmosphere.

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 concentration of the inorganic salt (sodium sulfate in the present embodiment) in the liquid to be treated can be reduced by lowering the temperature of the liquid to be treated after evaporation and concentration to lower the solubility until the inorganic salt contained in the liquid to be treated is crystallized. Therefore, when lithium carbonate is recovered in the carbonation step S11 described later, the purity of lithium carbonate can be improved.

In the crystallization step S9, the method for cooling and crystallizing the liquid to be treated is not particularly limited, and for example, the cooling and crystallizing device 6 can be used. The cooling crystallization apparatus 6 is an apparatus for cooling the supplied liquid to be treated in a crystallization tank to precipitate crystals of the target inorganic salt. As the cooling crystallization apparatus 6, for example, a known cooling crystallization apparatus having a cooling system such as a crystallization apparatus using a jacket or an internal coil, or an external circulation cooling type crystallization apparatus 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 saturated solubility and the temperature dependence of the solubility differ depending on the inorganic salt. In the present embodiment, the temperature dependency of the solubility of lithium salts such as lithium sulfate is utilized to be 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 in the form of 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 the crystals of sodium sulfate is 30 ℃ or lower, preferably 5 ℃ or higher and 20 ℃ or lower. At this time, sodium sulfate was replaced with sodium sulfate decahydrate (Na)₂SO₄·10H₂O) is precipitated.

In the subsequent solid-liquid separation step S10, the liquid to be treated after the crystallization step S9 is filtered, for example, to separate a precipitate containing crystals of an inorganic salt (sodium sulfate in the present embodiment) from the liquid to be treated.

In the next carbonation step S11, carbon dioxide and/or a water-soluble carbonate is added to the treatment target liquid from which the precipitate containing the crystals of the inorganic salt has been separated, whereby lithium in the treatment target liquid is precipitated and precipitated as crystals of lithium carbonate. Thus, lithium in the treatment liquid can be recovered as lithium carbonate. As the carbonate, for example, sodium carbonate, ammonium carbonate, potassium carbonate, or the like can be used.

In the carbonation step S11, carbon dioxide is preferably mixed with the liquid to be treated to precipitate and precipitate crystals of lithium carbonate. Thus, in the carbonation step S11, the use of a material containing no alkali metal such as sodium makes it possible to suppress the alkali metal other than lithium from being mixed into the precipitated lithium carbonate crystals. Thereby, lithium carbonate having high purity can be recovered.

However, there are the following cases: if the carbon dioxide gas is continuously mixed, the pH of the treatment target solution decreases, and therefore the deposition amount of lithium carbonate decreases. Therefore, it is preferable to stop the mixing of carbon dioxide before the pH of the liquid to be treated becomes 7 or less. Further, the pH can be prevented from decreasing by adding a base to the liquid to be treated. In this case, it is preferable to maintain the pH at 9 or more by adding a base. 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 into the liquid to be treated is not particularly limited, and a commonly performed method can be used. For example, carbon dioxide can be supplied to the liquid to be treated in the form of fine bubbles by a nozzle while stirring the liquid to be treated in the carbonation tank 7, whereby carbon dioxide can be uniformly mixed with the liquid to be treated, and lithium in the liquid to be treated can be efficiently reacted with carbon dioxide. Alternatively, the reaction with carbon dioxide may be carried out by spraying the liquid to be treated in a carbon dioxide atmosphere.

Since the solubility of lithium carbonate decreases as the temperature increases, the temperature of the treatment liquid is preferably increased in the carbonation step S11. This reduces the solubility of lithium carbonate generated by the reaction between lithium and carbon dioxide in the liquid to be treated, and can increase the amount of lithium carbonate crystals precipitated. Further, by raising the temperature of the liquid to be treated, the solubility of the inorganic salt (sodium sulfate in the present embodiment) remaining in the liquid to be treated can be increased, and crystallization of the inorganic salt can be suppressed. This can suppress the precipitation of crystals of the inorganic salt together with crystals of lithium carbonate, and therefore, when lithium carbonate is recovered in the carbonation step, the purity of lithium carbonate can be improved.

In the subsequent solid-liquid separation step S12, the liquid to be treated after the carbonation step S11 is filtered, for example, to separate a precipitate containing crystals of lithium carbonate from the lithium-containing liquid. In the solid-liquid separation step S12, impurities can be removed and the purity of lithium carbonate can be improved by washing the precipitate separated from the lithium-containing liquid with water or the like. The water used for washing the precipitates is not particularly limited, and it is preferable to use condensed water generated when the liquid to be treated is concentrated by evaporation in the concentration step S8, whereby the condensed water can be effectively used.

The liquid to be treated (filtrate) after the solid-liquid separation step S12 is not particularly limited, but it preferably contains impurities, and therefore, a part of the liquid is discharged as an effluent liquid and a part of the liquid is recirculated in the system. This enables recovery of lithium remaining in the liquid to be treated, and therefore enables recovery of lithium 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 again in the system, it may be supplied to the evaporation and concentration apparatus 5 to be evaporated and concentrated in the concentration step S8, but it is preferably supplied to the 1 st pH adjustment tank 2 and/or the 2 nd pH adjustment tank 3. The liquid to be treated after the solid-liquid separation step S12 is alkaline, and therefore can be used as the alkali to be added in the pH adjustment steps S3 and S5. In addition, the liquid to be treated after the solid-liquid separation step S12 contains a large amount of carbonate ions (CO)₃ ^2-) When the evaporation concentration is performed in the concentration step S8, crystals of carbonate are precipitated on the heat transfer surface of the heat exchanger of the evaporation and concentration apparatus 5. WhileSince the lithium-containing liquid after the solid-liquid separation steps S2 and S4 is acidic, the lithium-containing liquid can neutralize the liquid to be treated after the solid-liquid separation step S12, and carbonate ions can be released from the liquid to be treated as carbon dioxide, thereby preventing the precipitation of carbonate crystals on the heat transfer surface of the heat exchanger of the evaporation and concentration apparatus 5 in the concentration step S8.

On the other hand, crystals of the inorganic salt (sodium sulfate in the present embodiment) contained in the precipitate separated from the liquid to be treated in the solid-liquid separation step S10 (cooling crystallization apparatus 6) are supplied to the dissolution step S13 (dissolution tank 8). In the dissolving step S13, crystals of the inorganic salt are dissolved with, for example, water in the dissolving tank 8 to a desired concentration, thereby producing an inorganic salt solution. The temperature at this time is not particularly limited, and may be a temperature at which crystals of the inorganic salt can be dissolved. The water used for dissolving the inorganic salt is not particularly limited, but it is preferable to utilize condensed water generated when the liquid to be treated is concentrated by evaporation in the concentration step S8, whereby the condensed water can be effectively utilized. The resulting inorganic salt solution is supplied to the bipolar membrane electrodialysis device 9.

In the next electrodialysis step S14, the base and the inorganic acid are separated and recovered from the inorganic salt solution after the dissolution step S13 by the bipolar membrane electrodialysis device 9. As the bipolar membrane electrodialysis device 9, for example, a bipolar membrane electrodialysis device of a three-compartment cell system shown in fig. 3, in which a plurality of cells 90 are laminated, and the cells 90 include an anion exchange membrane 91, a

cation exchange membrane

92, and 2

bipolar membranes

93 and 94 between an anode 95 and a cathode 96, can be suitably used. In the bipolar membrane electrodialysis device 9 of the present embodiment, a desalting compartment R1 is formed by the anion exchange membrane 91 and the cation exchange membrane 92, an acid compartment R2 is formed between the anion exchange membrane 91 and one bipolar membrane 93, and an alkali compartment R3 is formed between the cation exchange membrane 92 and the other bipolar membrane 94. An anode chamber R4 and a cathode chamber R5 are formed outside the

bipolar membranes

93 and 94, respectively, an anode 95 is disposed in the anode chamber R4, and a cathode 96 is disposed in the cathode chamber R5.

In the electrodialysis step S14, an inorganic salt solution is introduced into the desalting chamber R1 and divided into acid chamber R2 and alkali chamber R3Pure water is introduced separately. Thus, in the case where the inorganic salt solution contains, for example, sodium sulfate, sodium ions (Na) are present in the desalting chamber R1⁺) Passing through cation exchange membrane 92, sulfate ion (SO)₄ ^2-) Through an 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) in the bipolar membranes 93 and 94⁺) And hydroxide ion (OH)^-) Hydrogen ion (H) in acid compartment R2⁺) With sulfate ions (SO)₄ ^2-) Combine to form sulfuric acid (H)₂SO₄) In the base chamber R3, hydroxide ion (OH)^-) With sodium ion (Na)⁺) Binding to form sodium hydroxide (NaOH). Thus, sulfuric acid (H) as an inorganic acid was recovered from the acid chamber R2₂SO₄) Sodium hydroxide (NaOH) was recovered as a base from the base chamber R3. The pure water introduced into the acid chamber R2 and the alkali chamber R3 can be condensed water generated when the liquid to be treated is concentrated by evaporation in the concentration step S8.

The desalted dilute inorganic salt solution (desalted liquid) discharged from the desalting chamber R1 is not particularly limited, but it is preferable to supply the dilute inorganic salt solution to the concentration step S8 (evaporation and concentration apparatus 5) because it contains a small amount of lithium, and to carbonate the dilute inorganic salt solution in the carbonation step S11 after the dilute inorganic salt solution is concentrated again. Thus, lithium can be recovered at a high recovery rate. Although the desalted liquid is supplied to the concentration step S8 in the present embodiment, the desalted liquid may be supplied to the impurity removal step S7 when calcium and/or magnesium remain in the desalted liquid. Thus, calcium and magnesium can be removed from the desalted liquid, and then the desalted liquid can be supplied to the concentration step S8. The desalted liquid may be supplied to the pH adjustment step S3 at step 1. Thus, when cobalt remains in the desalted liquid, the recovery rate of cobalt can be improved.

Although the inorganic acid (sulfuric acid in the present embodiment) recovered from the acid chamber R2 is not particularly limited, it is preferably supplied to the acid leaching tank 1 and reused as the inorganic acid for leaching the spent lithium ion battery in the acid leaching step S1. It is preferable that the regenerated solution is supplied to the polyvalent cation removal device 4 and reused as a regenerated solution of the chelate resin or the ion exchange resin used in the impurity treatment step S7.

The alkali (sodium hydroxide in the present embodiment) recovered from the alkali chamber R3 is not particularly limited, but is preferably supplied to the

pH adjustment tanks

2 and 3 and reused as an alkali for adjusting the pH of the lithium-containing liquid in the pH adjustment steps S3 and S5. It is preferable that the regenerated solution is supplied to the polyvalent cation removal device 4 and reused as a regenerated solution of the chelate resin or the ion exchange resin used in the impurity treatment step S7.

According to the lithium recovery method of the present embodiment described above, the liquid to be treated is evaporated and concentrated in the concentration step S8 before the carbonation step S11, whereby the amount of liquid in the liquid to be treated is reduced and the lithium concentration in the liquid to be treated is increased. This can improve the recovery rate of lithium carbonate crystals in the carbonation step S11.

In the crystallization step S9 after the concentration step S8, the temperature of the liquid to be treated after evaporation and concentration is lowered by cooling and crystallizing the liquid to be treated, and the solubility is lowered until the inorganic salt (sodium sulfate in the present embodiment) contained in the liquid to be treated is crystallized, so that the concentration of the inorganic salt in the liquid to be treated can be lowered. In addition, since the temperature of the treatment target liquid is increased to decrease the solubility of lithium carbonate in the carbonation step S11, the solubility of the inorganic salt remaining in the treatment target liquid is increased, and the crystallization of the inorganic salt can be suppressed. This can improve the purity of lithium carbonate when lithium carbonate is recovered in the carbonation step S11.

In addition, according to the lithium recovery method of the present embodiment, the liquid to be treated from which the lithium carbonate crystals have been recovered is not discarded in the carbonation step S11, but is circulated in the system to recover lithium remaining in the liquid to be treated. Thus, lithium can be recovered at a high recovery rate.

In addition, according to the lithium recovery method of the present embodiment, after the crystals of the inorganic salt (sodium sulfate in the present embodiment) contained in the precipitate separated from the treatment liquid in the solid-liquid separation step S10 are dissolved in the dissolution step S13 to form an inorganic salt solution, bipolar membrane electrodialysis is performed in the electrodialysis step S14 to recover the inorganic acid and the alkali from the inorganic salt solution, and the desalted diluted inorganic salt solution is evaporated and concentrated in the concentration step S8 to recover lithium contained in the diluted inorganic salt solution in the carbonation step S11. Thus, lithium can be recovered at a high recovery rate. Further, the amount of the inorganic acid and the alkali used in the steps S1, S3, S5, and S7 can be reduced by recycling the inorganic acid and the alkali recovered in the electrodialysis step S14 to the acid leaching step S1, the pH adjusting steps S3 and S5, and the impurity removal step S7 for reuse.

In addition, according to the lithium recovery method of the present embodiment, polyvalent cations such as calcium and magnesium contained in the liquid to be treated are removed in the impurity removal step S7. Accordingly, the amount of impurities in the liquid to be treated from which precipitates are separated in the solid-liquid separation step S12 after the carbonation step S11 is reduced, and thus more liquid to be treated after the solid-liquid separation step S12 can be circulated again in the system. This enables more lithium remaining in the liquid to be treated after the solid-liquid separation step S12 to be recovered, and therefore enables lithium to be recovered at a high recovery rate. Furthermore, since the amount of impurities in the inorganic solution subjected to electrodialysis in the electrodialysis step S14 is also reduced, the performance of the bipolar membrane electrodialysis device 9 can be prevented from being reduced due to scaling of the cation exchange membrane, and the performance of the bipolar membrane can be maintained high.

In addition, according to the lithium recovery method of the present embodiment, since the condensed water generated in the concentration step S8 is used for various processes, the condensed water can be effectively used. Further, by washing the crystals obtained in the respective solid-liquid separation steps S4, S6, S10, and S12 with condensed water, the recovery rate of each crystal can be improved favorably.

Although the embodiment of the lithium recovery method according to the first embodiment has been described above, the lithium recovery method according to the first embodiment is not limited to the embodiment shown in fig. 1 and 2, and various modifications can be made without departing from the scope of the present disclosure.

For example, although the impurity removal step S7 for removing at least calcium and/or magnesium is performed on the liquid to be treated before the concentration step S8 in the embodiment of fig. 1 and 2, an impurity removal step for removing at least calcium and/or magnesium may be similarly performed on the inorganic salt solution before the electrodialysis step S14 instead of or in addition to this step.

In the embodiment of fig. 1 and 2, the alkali recovered in the electrodialysis step S14 is supplied to the 1 st pH adjustment step S3 and the 2 nd pH adjustment step S5, but may be supplied only to either step.

In the embodiment of fig. 1 and 2, the pH adjustment steps S3 and S5 include the 1 st pH adjustment step S3 and the 2 nd pH adjustment step S5, but may be configured to include 3 or more steps or only 1 step depending on the components contained in the waste lithium ion battery.

In the embodiment of fig. 1 and 2, as shown in fig. 4 and 5, a treatment step for removing impurities such as silica contained in the inorganic salt solution may be performed after the dissolution step S13 and before the electrodialysis step S14. This treatment step may be performed in place of the impurity removal step S7 or in addition to the impurity removal step S7.

Specifically, first, in the recrystallization step S13-1, the inorganic salt (sodium sulfate in the present embodiment) contained in the inorganic salt solution is recrystallized. The method for recrystallizing the inorganic salt contained in the inorganic salt solution is not particularly limited, and for example, the cooling crystallization by the cooling crystallization apparatus 10 similar to the cooling crystallization apparatus 6 of the crystallization step S9 can be used. That is, only crystals of the inorganic salt may be precipitated by utilizing the difference in the saturation solubility and the temperature dependency of the solubility between the inorganic salt and silica, and the crystals of the inorganic salt may be precipitated by cooling to a temperature equal to or higher than the precipitation temperature of silica at the supply concentration and equal to or lower than the precipitation temperature of the inorganic salt. At this time, sodium sulfate was replaced with sodium sulfate decahydrate (Na)₂SO₄·10H₂O) is precipitated. 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 crystallization apparatus 10 is used in the recrystallization step S13-1, but a crystallization method for precipitating high-purity crystals may be used, and for example, an evaporation crystallization apparatus or the like may be used.

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

Then, in the redissolution step S13-3, the crystals of the recovered inorganic salt are dissolved with, for example, water in the redissolution tank 11 to have a desired concentration, thereby regenerating an inorganic salt solution. The temperature at this time is not particularly limited as long as the temperature is a temperature at which crystals of the inorganic salt can be dissolved. The water used for dissolving the inorganic salt is not particularly limited, but it is preferable to utilize condensed water generated when the liquid to be treated is concentrated by evaporation in the concentration step S8, whereby the condensed water can be effectively utilized. The regenerated inorganic salt solution is supplied to the bipolar membrane electrodialysis device 9. In the recrystallization step S13-1 to the redissolution step S13-3, the impurities removed from the inorganic salt solution may contain calcium and/or magnesium in addition to silica.

In the embodiment of fig. 4 and 5, silica contained in the inorganic salt solution is removed before the electrodialysis step S14. Accordingly, the amount of impurities in the inorganic solution subjected to electrodialysis in the electrodialysis step S14 is also reduced, and thus the performance of the bipolar membrane can be maintained high. Further, when the dilute inorganic salt solution (desalted solution) after the electrodialysis step S14 is supplied to the evaporation concentration apparatus 5 and evaporation concentration is performed again in the concentration step S8, the amount of impurities in the desalted solution is reduced, and generation and adhesion of scale on the heat transfer surface of the heat exchanger of the evaporation concentration apparatus 5 can be suppressed in the concentration step S8. Further, the amount of impurities in the liquid to be treated from which precipitates are separated in the solid-liquid separation step S12 after the carbonation step S11 is reduced, and more liquid to be treated after the solid-liquid separation step S12 can be circulated again in the system. This enables more lithium remaining in the liquid to be treated after the solid-liquid separation step S12 to be recovered, and enables lithium to be recovered at a high recovery rate.

In the embodiment of fig. 1 and 2, as shown in fig. 6 and 7, a firing step S0 of firing the spent lithium ion batteries may be further provided before the acid leaching step S1. In the firing step S0, the method for firing the spent lithium ion battery is not particularly limited, and a known firing apparatus 12 may be used.

In the embodiment shown in fig. 6 and 7, the exhaust gas generated in the baking device 12 (baking step S0) is supplied to the carbonating tank 7, and the exhaust gas is mixed as carbon dioxide into the liquid to be treated in the carbonating step S11. This can reduce the amount of carbon dioxide used in the carbonation step S11. It should be noted that, in the embodiment of fig. 4 and 5, the firing step S0 of firing the spent lithium ion batteries may be performed before the acid leaching step S1, as a matter of course.

Method for recovering lithium according to embodiment 2

A lithium recovery method according to claim 2 of the present disclosure is characterized by including the steps of: a concentration step of heating a liquid to be treated in which at least lithium and an inorganic salt are dissolved at a low pressure lower than atmospheric pressure to thereby evaporate and concentrate the liquid; a carbonation step of mixing carbon dioxide and/or adding a water-soluble carbonate to the liquid to be treated after the concentration step; and a solid-liquid separation step of separating precipitates containing crystals of lithium carbonate precipitated in the carbonation step from the liquid to be treated, wherein in the carbonation step, the temperature of the liquid to be treated is set to be equal to or higher than the evaporation temperature of the liquid to be treated in the concentration step.

In the lithium recovery method according to paragraph 0089, the concentration step preferably includes evaporating and concentrating the liquid to be treated under a pressure of 10kPa to 70 kPa.

In the lithium recovery method according to paragraph 0089 or 0090, it is preferable that at least a part of the liquid to be treated after the solid-liquid separation step is evaporated and concentrated in the concentration step.

Further, the lithium recovery method according to any one of 0089 to 0091, preferably further comprising the steps of: a dissolving step of precipitating the inorganic salt contained in the liquid to be treated as crystals in the concentrating step, and dissolving the inorganic salt contained as crystals in the precipitate separated from the liquid to be treated after the concentrating step to produce an inorganic salt solution; and an electrodialysis step of subjecting the inorganic salt solution obtained in the dissolving step to bipolar membrane electrodialysis, thereby separating and recovering the inorganic acid from the inorganic salt solution together with the alkali.

Further, in the lithium recovery method according to any one of paragraphs 0089 to 0092, it is preferable that the method further comprises, before the concentration step, the steps of: an acid leaching step of leaching the spent lithium ion battery with an inorganic acid to leach lithium; and a pH adjustment step of adding a base to the lithium-containing liquid obtained in the acid leaching step to adjust the pH, and separating the precipitate precipitated in the pH adjustment step from the lithium-containing liquid to produce a liquid to be treated.

In the lithium recovery method according to paragraph 0093, it is preferable that at least a part of the liquid to be treated after the solid-liquid separation step is reused as the alkali to be added in the pH adjustment step.

In the method for recovering lithium according to paragraph 0093 or 0094, it is preferable that the base recovered in the electrodialysis step is reused as the base to be added in the pH adjustment step, and the inorganic acid recovered in the electrodialysis step is reused as the inorganic acid to be used in the acid leaching step.

According to the lithium recovery method of claim 2 of the present disclosure, the liquid to be treated is evaporated and concentrated in the concentration step before the carbonation step, thereby reducing the amount of the liquid to be treated and increasing the lithium concentration in the liquid to be treated. This can improve the recovery rate of lithium carbonate in the carbonation step.

In the concentration step, the liquid to be treated is evaporated and concentrated at a low pressure, whereby the temperature of the liquid to be treated after evaporation and concentration can be lowered as compared with the case where the liquid to be treated is evaporated and concentrated at atmospheric pressure. Therefore, a large space for increasing the temperature of the liquid to be treated can be secured in the subsequent carbonation step, and the evaporation temperature of the liquid to be treated (the boiling point of water contained in the liquid to be treated) is lowered at a low pressure, so that the energy required for evaporation and concentration of the liquid to be treated can be suppressed to a low level, and energy saving can be achieved. In the carbonation step, when the temperature of the liquid to be treated is low, the inorganic salt contained in the liquid to be treated is crystallized, and the temperature of the liquid to be treated at the time of carbonation is increased as compared with the evaporation temperature of the liquid to be treated at the concentration step, whereby the solubility of the inorganic salt remaining in the liquid to be treated is improved, and the crystallization of the inorganic salt at the time of carbonation can be suppressed. In addition, when the temperature of the treatment target liquid is high during carbonation, the solubility of lithium carbonate decreases, and the recovery amount of lithium carbonate crystals can be increased. This can enhance the effect of obtaining high-purity lithium carbonate in high yield.

Fig. 8 shows steps of respective steps in an embodiment of a lithium recovery method according to embodiment 2 of the present disclosure, and fig. 9 shows a schematic configuration of a processing apparatus 10 for implementing the lithium recovery method of fig. 8. The lithium recovery method according to the present embodiment is suitable for lithium, and can be suitably used for treating a liquid to be treated containing a strong acid such as hydrochloric acid, sulfuric acid, hydrofluoric acid, or phosphoric acid and an inorganic salt of an alkali metal or an alkaline earth metal such as potassium or sodium, and particularly for recovering lithium from a waste lithium ion battery. The following description will be given taking a case of recovering lithium from a waste lithium ion battery as an example.

The lithium recovery method of the present embodiment includes:

a solid-liquid separation step S9 of separating a precipitate containing crystals of the inorganic salt from the liquid to be treated after the concentration step S8;

a carbonation step S10 of mixing carbon dioxide and/or adding a water-soluble carbonate to the liquid to be treated after the solid-liquid separation step S9; and the combination of (a) and (b),

a solid-liquid separation step S11 of separating a precipitate containing crystals of lithium carbonate precipitated in the carbonation step S10 from the liquid to be treated. The lithium recovery method of the present embodiment further includes:

a dissolving step S12 of dissolving crystals of the inorganic salt contained in the precipitate separated from the liquid to be treated in the solid-liquid separation step S9 to form an inorganic salt solution; and the combination of (a) and (b),

an electrodialysis step S13 of separating and recovering the base and the inorganic acid from the inorganic salt solution after the dissolving step S12 by subjecting the inorganic salt solution to bipolar membrane electrodialysis.

The waste lithium ion battery to be recovered is the same as that in embodiment 1 described above.

First, in the acid leaching step S1, the spent lithium ion battery is leached with an inorganic acid, whereby lithium and metals such as aluminum, nickel, cobalt, and iron are eluted. As the inorganic acid, for example, sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, or the like can be used, and hydrochloric acid is used in the present embodiment.

In the acid leaching step S1, the method of leaching the spent lithium ion battery with the inorganic acid is not particularly limited, and a commonly used method can be used. For example, the spent lithium ion battery is immersed in an aqueous solution of an inorganic acid such as an aqueous hydrochloric acid solution in the acid leaching tank 1 and stirred for a predetermined time to obtain a lithium-containing liquid in which the above-described metal such as lithium is dissolved.

In the subsequent solid-liquid separation step S2, the lithium-containing liquid obtained in the acid leaching step S1 is filtered, for example, to separate insoluble residues from the lithium-containing liquid. The insoluble residue is mainly a carbon material, a metal material, or an organic material insoluble in an inorganic acid. As a method for performing solid-liquid separation, for example, various filtration apparatuses such as pressure filtration (filter press), vacuum filtration, and centrifugal filtration, and known solid-liquid separation apparatuses such as centrifugal separation apparatuses of a decanter type can be used. The same applies to the following solid-liquid separation steps S4, S6, S9, S11, and the like.

pH adjustment tanks

The precipitate precipitated in the pH adjustment step S3 in the 1 st pH adjustment step S4 is separated from the lithium-containing liquid by, for example, filtering the lithium-containing liquid. The impurity metals removed from the lithium-containing liquid in the pH adjustment step S3 of step 1 may further include copper or the like. In the solid-liquid separation step S4, it is preferable to wash the precipitate with a cleaning liquid and supply the washed waste washing liquid together with the lithium-containing liquid (filtrate) to the next pH adjustment step S5 of 2. Thus, lithium contained in the waste washing liquid may be supplied from the pH 2 adjustment step S5 to the carbonation step S10 together with lithium contained in the lithium-containing liquid, and the lithium may be recovered at a high recovery rate by performing carbonation in the carbonation step S10 described later. The water used for washing the precipitates is not particularly limited, but is preferably condensed water generated when the liquid to be treated is concentrated by evaporation in the concentration step S8 described later, whereby the condensed water can be effectively used.

In the pH 2 adjustment step S5, a base is added to the lithium-containing liquid after the solid-liquid separation step S4 to adjust the pH to 7 or more, preferably 7 to 13, more preferably 7 to 11, and still more preferably 8 to 10. Thereby, the noble metal (e.g., cobalt and nickel) in the lithium-containing liquid is precipitated and precipitated in the form of crystals of an inorganic salt such as a hydroxide (e.g., cobalt hydroxide and nickel hydroxide). In the 2 nd pH adjustment step S5, the lithium-containing liquid is preferably heated to a constant temperature of, for example, 30 to 80 ℃. The alkali concentration of the aqueous alkali solution to be added in the 2 nd pH adjustment step S5 is not particularly limited, but is preferably equal to or higher than the alkali concentration of the aqueous alkali solution used in the 1 st pH adjustment step S3, and more preferably 0.2mol/L or higher.

On the other hand, in the lithium-containing liquid after the solid-liquid separation step S6, in addition to lithium, an inorganic salt (sodium chloride (NaCl) in the present embodiment) is dissolved in the lithium-containing liquid due to the inorganic acid (hydrochloric acid in the present embodiment) and the alkali (sodium hydroxide in the present embodiment) added in the acid leaching step S1 and the pH adjustment steps S3 and S5. The lithium-containing liquid after the pH adjustment steps S3 and S5 corresponds to the "liquid to be treated" in the lithium recovery method of the present disclosure. At least 1 of calcium, magnesium, and silica may be further dissolved in the liquid to be treated.

In the solid-liquid separation step S6, it is preferable to wash the precipitate with a cleaning liquid and supply the washed waste cleaning liquid together with the liquid to be treated (filtrate) to the next impurity removal step S8. Thus, lithium contained in the waste cleaning liquid can be supplied from the impurity removal step S8 to the carbonation step S10 together with lithium contained in the liquid to be treated, and lithium can be recovered at a high recovery rate by carbonation in the carbonation step S10 described later. The water used for washing the precipitates is not particularly limited, and it is preferable to utilize condensed water generated when the liquid to be treated is concentrated by evaporation in the concentration step S8 described later, whereby the condensed water can be effectively utilized.

In the subsequent impurity removal step S7, at least polyvalent cations such as calcium and/or magnesium contained in the liquid to be treated after the solid-liquid separation step S6 are removed. By removing calcium, magnesium, and the like contained as impurities in the liquid to be treated, generation and adhesion of scale on the heat transfer surface of the heat exchanger of the evaporation and concentration device 5 can be suppressed in the concentration step S8 described later, and the heat exchange efficiency can be maintained high. Further, if the liquid to be treated contains calcium, magnesium, or the like, polyvalent cations such as calcium, magnesium, or the like contained in the inorganic solution are precipitated in the cation exchange membrane of the bipolar membrane electrodialysis device 9 in the electrodialysis step S13 described later, which may cause a decrease in membrane performance. Therefore, by starting electrodialysis of calcium, magnesium, or the like in advance, substances causing troubles such as scaling can be removed from the treatment liquid, thereby preventing adverse effects on the cation exchange membrane of the bipolar membrane electrodialysis device 9 and maintaining the performance of electrodialysis high.

In the impurity removal step S7, the method for removing calcium and magnesium from the treatment liquid is not particularly limited, and, for example, the polyvalent cation removal device 4 can be used. The polyvalent cation removal device 4 is a device for removing polyvalent cations having a valence of 2 or more, such as calcium ions and magnesium ions, and may include, for example: and a device having an ion exchange resin therein and configured to be capable of adsorbing calcium ions and magnesium ions by bringing the liquid to be treated into contact with the ion exchange resin. As the polyvalent cation removal means 4, there can be exemplified: a device capable of introducing a liquid to be treated into a column filled with a chelate resin. As the chelate resin, a chelate resin capable of selectively capturing calcium ions and magnesium ions can be used, and examples thereof include iminodiacetic acid type and aminophosphonic acid type. The polyvalent cation removal device 4 may be added with a chelating agent. The impurities removed from the treatment liquid in the impurity removal step S7 may include silicon dioxide (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 heated and evaporated, that is, the liquid to be treated is concentrated by evaporating water in the liquid to be treated. This reduces the amount of liquid in the treatment target liquid and increases the lithium concentration in the treatment target liquid. This can improve the recovery rate of lithium carbonate in the carbonation step S10 described later.

In the concentration step S8, the liquid to be treated is preferably evaporated and concentrated to a concentration at which lithium is not precipitated in the concentrated liquid to be treated, for example, in the form of crystals of a lithium salt such as lithium chloride. This can increase the lithium concentration in the concentrated liquid to be treated, and the recovery rate of lithium carbonate can be increased in the carbonation step S10 described later.

In the concentration step S8, the inorganic salt in the liquid to be treated may be crystallized by the concentration increase due to evaporation and concentration of the liquid to be treated. The inorganic salt contained in the liquid to be treated may or may not precipitate as crystals in the concentration step S8. In the present embodiment, the inorganic salt contained in the liquid to be treated is precipitated as crystals in the concentration step S8, and the precipitate is separated from the liquid to be treated in the subsequent solid-liquid separation step S9.

In the concentration step S8, the method of evaporating and concentrating the liquid to be treated is not particularly limited, and, for example, the evaporation and concentration apparatus 5 can be used. The evaporation concentration device 5 is not particularly limited as long as it can concentrate the liquid to be treated by evaporation, and known evaporation concentration devices such as a heat pump type, an ejector (injector) type, a steam type, and a flash evaporation type can be used. When the heat pump type evaporation and concentration apparatus is used, the energy used can be significantly suppressed.

The evaporation and concentration apparatus 5 is connected to a vacuum pump, not shown, to maintain the inside at a low pressure, and in the concentration step S8, the liquid to be treated is evaporated and concentrated by heating the liquid to be treated at a low pressure lower than the atmospheric pressure. The temperature of the liquid to be treated rises when the liquid to be treated is subjected to evaporation concentration, but the evaporation temperature of the liquid to be treated (the boiling point of water contained in the liquid to be treated) is lower at low pressure than at atmospheric pressure, so that the temperature of the liquid to be treated after evaporation concentration can be lowered by performing evaporation concentration at low pressure. Therefore, a large temperature rise space for the treatment target liquid can be secured in the carbonation step S10 described later. Further, since the evaporation temperature of the liquid to be treated is lowered at low pressure, the energy required for evaporation and concentration of the liquid to be treated can be kept low, and energy saving can be achieved.

The internal pressure of the evaporation and concentration device 5, that is, the atmospheric pressure when the liquid to be treated is evaporated and concentrated is not particularly limited, but is preferably 10kPa or more and 70kPa or less, and more preferably 15kPa or more and 50kPa or less. From the viewpoint of the relationship with the above-described pressure (saturated vapor pressure curve), the evaporation temperature of the treatment target liquid is preferably 45 ℃ or higher and 95 ℃ or lower, and more preferably 55 ℃ or higher and 80 ℃ or lower.

By setting the pressure to 10kPa or more, the temperature of the liquid to be treated after the evaporation and concentration can be set to an appropriate low temperature without excessively decreasing, and therefore, the energy required for increasing the temperature of the liquid to be treated in the carbonation step S10 described later can be suppressed to be low. Further, since the evaporation and concentration apparatus 5 does not need to be an apparatus having a very high pressure resistance, the manufacturing cost of the apparatus can be kept low. On the other hand, by setting the pressure to 70kPa or less, the temperature of the liquid to be treated after the evaporation and concentration can be set to an appropriate low temperature without excessively increasing the temperature, and therefore, a large temperature increase space for the liquid to be treated can be sufficiently secured in the carbonation step S10 described later. Further, energy required for evaporation and concentration of the liquid to be treated is not excessively increased, and energy saving can be effectively achieved.

Although not shown, a temperature sensor is provided in a liquid reservoir of the liquid to be treated at the bottom of the evaporation and concentration device 5 or in a liquid supply path between the evaporation and concentration device 5 and a carbonator 7 described later, and the evaporation temperature of the liquid to be treated (the temperature of the liquid to be treated after evaporation and concentration) is monitored by the temperature sensor. Although not shown, a pressure sensor is provided in the upper space of the evaporation and concentration device 5, and the internal pressure of the evaporation and concentration device 5 (the atmospheric pressure when the liquid to be treated is evaporated and concentrated) is monitored by the pressure sensor.

In the subsequent solid-liquid separation step S9, the liquid to be treated after the concentration step S8 is filtered, for example, to separate a precipitate containing crystals of an inorganic salt (sodium chloride in the present embodiment) from the liquid to be treated.

In the next carbonation step S10, carbon dioxide and/or a water-soluble carbonate is added to the treatment target liquid from which the precipitate containing the crystals of the inorganic salt has been separated, whereby lithium in the treatment target liquid is precipitated and precipitated as crystals of lithium carbonate. Thus, lithium in the treatment liquid can be recovered as lithium carbonate. As the carbonate, for example, sodium carbonate, ammonium carbonate, potassium carbonate, or the like can be used.

In the carbonation step S10, carbon dioxide is preferably mixed with the liquid to be treated to precipitate and precipitate crystals of lithium carbonate. Thus, in the carbonation step S10, the use of a material containing no alkali metal such as sodium makes it possible to suppress the alkali metal other than lithium from being mixed into the precipitated lithium carbonate crystals. Thereby, lithium carbonate having high purity can be recovered.

In the carbonation step S10, the method of mixing carbon dioxide into the liquid to be treated is not particularly limited, and a commonly performed method can be used. For example, carbon dioxide can be supplied to the liquid to be treated in the form of fine bubbles by a nozzle while stirring the liquid to be treated in the carbonation tank 7, whereby carbon dioxide can be uniformly mixed with the liquid to be treated, and lithium in the liquid to be treated can be efficiently reacted with carbon dioxide. Alternatively, the reaction with carbon dioxide may be carried out by spraying the liquid to be treated in a carbon dioxide atmosphere.

In the carbonation step S10, the temperature of the liquid to be treated is set to be equal to or higher than the evaporation temperature of the liquid to be treated in the concentration step S8. If the temperature of the liquid to be treated is low during carbonation, the inorganic salt (sodium chloride in the present embodiment) contained in the liquid to be treated may crystallize. Therefore, by raising the temperature of the liquid to be treated in the carbonation step S10 to make the temperature of the liquid to be treated higher than the evaporation temperature of the liquid to be treated at the time of carbonation, the solubility of the inorganic salt remaining in the liquid to be treated at the time of carbonation increases, and crystallization of the inorganic salt can be suppressed. This can improve the purity of lithium carbonate when lithium carbonate is recovered in the carbonation step S10.

The temperature of the liquid to be treated at the time of carbonation is not particularly limited as long as it is equal to or higher than the evaporation temperature of the liquid to be treated, and is preferably lower than 100 ℃. The method of raising the temperature of the treatment target liquid in the carbonation step S10 is not particularly limited, and for example, a method of heating the treatment target liquid in the carbonation tank 7 by using a known heating means such as a heater may be used. The temperature of the liquid to be treated may be increased by a preheating means such as a heat exchanger before the liquid to be treated is supplied to the carbonating tank 7.

Further, the solubility of lithium carbonate decreases as the temperature of the treatment target liquid increases. Therefore, by increasing the temperature of the treatment target liquid in the carbonation step S10, the solubility of lithium carbonate generated by the reaction between lithium and carbon dioxide in the treatment target liquid can be reduced. This can increase the amount of lithium carbonate crystals precipitated.

This can increase the recovery amount of lithium carbonate crystals and suppress the precipitation amount of inorganic salt crystals, and therefore high-purity lithium carbonate can be obtained with high efficiency.

In the subsequent solid-liquid separation step S11, the liquid to be treated after the carbonation step S10 is filtered, for example, to separate a precipitate containing crystals of lithium carbonate from the lithium-containing liquid. In the solid-liquid separation step S11, impurities can be removed and the purity of lithium carbonate can be improved by washing the precipitate separated from the lithium-containing liquid with water or the like. The water used for washing the precipitates is not particularly limited, and it is preferable to use condensed water generated when the liquid to be treated is concentrated by evaporation in the concentration step S8, whereby the condensed water can be effectively used.

The liquid to be treated (filtrate) after the solid-liquid separation step S11 is not particularly limited, but it preferably contains impurities, and therefore, a part of the liquid is discharged as an effluent liquid and a part of the liquid is recirculated in the system. This enables recovery of lithium remaining in the liquid to be treated, and therefore enables recovery of lithium 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 S11.

When the liquid to be treated after the solid-liquid separation step S11 is circulated again in the system, it may be supplied to the evaporation and concentration apparatus 5 to be evaporated and concentrated in the concentration step S8, but it is preferably supplied to the 1 st pH adjustment tank 2 and/or the 2 nd pH adjustment tank 3. The liquid to be treated after the solid-liquid separation step S11 is alkaline, and therefore can be used as the alkali to be added in the pH adjustment steps S3 and S5. In addition, the liquid to be treated after the solid-liquid separation step S11 contains a large amount of carbonate ions (CO)₃ ^2-) When the evaporation concentration is performed in the concentration step S8, crystals of carbonate are precipitated on the heat transfer surface of the heat exchanger of the evaporation and concentration apparatus 5. Since the lithium-containing liquid after the solid-liquid separation steps S2 and S4 is acidic, the lithium-containing liquid can neutralize the liquid to be treated after the solid-liquid separation step S11, and carbonate ions can be released from the liquid to be treated as carbon dioxide, thereby preventing the precipitation of carbonate crystals on the heat transfer surface of the heat exchanger of the evaporation and concentration apparatus 5 in the concentration step S8.

On the other hand, crystals of an inorganic salt (sodium chloride in the present embodiment) contained in the precipitate generated in the concentration step S8 (evaporation/concentration apparatus 5) and separated from the liquid to be treated in the solid-liquid separation step S9 are supplied to the dissolution step S12 (dissolution tank 8). In the dissolving step S12, crystals of the inorganic salt are dissolved with, for example, water in the dissolving tank 8 to a desired concentration, thereby producing an inorganic salt solution. The temperature at this time is not particularly limited, and may be a temperature at which crystals of the inorganic salt can be dissolved. The water used for dissolving the inorganic salt is not particularly limited, but it is preferable to utilize condensed water generated when the liquid to be treated is concentrated by evaporation in the concentration step S8, whereby the condensed water can be effectively utilized. The resulting inorganic salt solution is supplied to the bipolar membrane electrodialysis device 9.

In the next electrodialysis step S13, the base and the inorganic acid are separated and recovered from the inorganic salt solution after the dissolution step S12 by the bipolar membrane electrodialysis device 9. As the bipolar membrane electrodialysis device 9, for example, a bipolar membrane electrodialysis device of a three-compartment cell system shown in fig. 10, in which a plurality of cells 90 are laminated, and the cells 90 include an anion exchange membrane 91, a

cation exchange membrane

92, and 2

bipolar membranes

In the electrodialysis step S13, an inorganic salt solution is introduced into the desalting chamber R1, and pure water is introduced into the acid chamber R2 and the alkali chamber R3, respectively. Thus, in the case where the inorganic salt solution contains, for example, sodium chloride, sodium ions (Na) are present in the desalting chamber R1⁺) Passing through cation exchange membrane 92, chloride ion (Cl)^-) Through an 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) in the bipolar membranes 93 and 94⁺) And hydroxide ion (OH)^-) Hydrogen ion (H) in acid compartment R2⁺) With chloride ions (Cl)^-) Combine to form hydrochloric acid (HCl) and hydroxide ions (OH) in a base compartment R3^-) With sodium ion (Na)⁺) Binding to form sodium hydroxide (NaOH). Thus, hydrochloric acid (HCl) as an inorganic acid is recovered from the acid chamber R2, and sodium hydroxide (NaOH) as a base is recovered from the base chamber R3. The pure water introduced into the acid chamber R2 and the alkali chamber R3 can be condensed water generated when the liquid to be treated is concentrated by evaporation in the concentration step S8.

The desalted dilute inorganic salt solution (desalted liquid) discharged from the desalting chamber R1 is not particularly limited, but it is preferable to supply the desalted dilute inorganic salt solution to the evaporation and concentration device 5 and perform evaporation and concentration again in the concentration step S8 because it contains a small amount of lithium.

Although the inorganic acid (hydrochloric acid in the present embodiment) recovered from the acid chamber R2 is not particularly limited, it is preferably supplied to the acid leaching tank 1 and reused as the inorganic acid for leaching the spent lithium ion battery in the acid leaching step S1. It is preferable that the regenerated solution is supplied to the polyvalent cation removal device 4 and reused as a regenerated solution of the chelate resin or the ion exchange resin used in the impurity treatment step S7.

pH adjustment tanks

According to the lithium recovery method of the present embodiment described above, the liquid to be treated is evaporated and concentrated in the concentration step S8 before the carbonation step S10, whereby the amount of liquid in the liquid to be treated is reduced and the lithium concentration in the liquid to be treated is increased. This can improve the recovery rate of lithium carbonate crystals in the carbonation step S10.

In addition, in the carbonation step S10, since the inorganic salt (sodium chloride in the present embodiment) contained in the liquid to be treated is crystallized when the temperature of the liquid to be treated is low, the solubility of the inorganic salt remaining in the liquid to be treated is improved by raising the temperature of the liquid to be treated to be higher than the evaporation temperature during carbonation, and the crystallization of the inorganic salt during carbonation can be suppressed. In addition, during carbonation, when the temperature of the treatment target liquid is high, the solubility of lithium carbonate decreases, and the recovery amount of lithium carbonate crystals also increases. Thus, high-purity lithium carbonate can be obtained with high efficiency.

In addition, according to the lithium recovery method of the present embodiment, the liquid to be treated from which the lithium carbonate crystals have been recovered is not discarded in the carbonation step S10, but is circulated through the system, for example, the 1 st pH adjustment tank 2, the 2 nd pH adjustment tank 3, the evaporation and concentration apparatus 5, and the like, to recover lithium remaining in the liquid to be treated. Thus, lithium can be recovered at a high recovery rate.

In addition, according to the lithium recovery method of the present embodiment, after the crystals of the inorganic salt (sodium chloride in the present embodiment) contained in the precipitate separated from the treatment liquid in the solid-liquid separation step S9 are dissolved in the dissolution step S12 to form an inorganic salt solution, bipolar membrane electrodialysis is performed in the electrodialysis step S13 to recover the inorganic acid and the alkali from the inorganic salt solution, and the desalted dilute inorganic salt solution is evaporated and concentrated in the concentration step S8 to recover lithium contained in the dilute inorganic salt solution in the carbonation step S10. Thus, lithium can be recovered at a high recovery rate. Further, the amount of the inorganic acid and the alkali used in the steps S1, S3, S5, and S7 can be reduced by recycling the inorganic acid and the alkali recovered in the electrodialysis step S13 to the acid leaching step S1, the pH adjusting steps S3 and S5, and the impurity removal step S7 for reuse.

In addition, according to the lithium recovery method of the present embodiment, polyvalent cations such as calcium and magnesium contained in the liquid to be treated are removed in the impurity removal step S7. Accordingly, the amount of impurities in the liquid to be treated from which precipitates are separated in the solid-liquid separation step S11 after the carbonation step S10 is reduced, and thus more liquid to be treated after the solid-liquid separation step S11 can be circulated again in the system. This enables more lithium remaining in the liquid to be treated after the solid-liquid separation step S11 to be recovered, and therefore enables lithium to be recovered at a high recovery rate. Furthermore, since the amount of impurities in the inorganic solution subjected to electrodialysis in the electrodialysis step S13 is also reduced, the performance of the bipolar membrane electrodialysis device 9 can be prevented from being reduced due to scaling of the cation exchange membrane, and the performance of the bipolar membrane can be maintained high.

In addition, according to the lithium recovery method of the present embodiment, since the condensed water generated in the concentration step S8 is used for various processes, the condensed water can be effectively used. Further, by washing the crystals obtained in the respective solid-liquid separation steps S4, S6, S9, and S11 with condensed water, the recovery rate of each crystal can be improved favorably.

Although the embodiment of the lithium recovery method according to embodiment 2 has been described above, the lithium recovery method according to embodiment 2 is not limited to the embodiment of fig. 8 and 9, and various modifications can be made without departing from the scope of the present disclosure.

For example, although the impurity removal step S7 for removing at least calcium and/or magnesium is performed on the liquid to be treated before the concentration step S8 in the embodiment of fig. 8 and 9, an impurity removal step for removing at least calcium and/or magnesium may be similarly performed on the inorganic salt solution before the electrodialysis step S13 instead of or in addition to this step.

In the embodiment of fig. 8 and 9, the alkali recovered in the electrodialysis step S13 is supplied to the 1 st pH adjustment step S3 and the 2 nd pH adjustment step S5, but may be supplied only to either step.

In the embodiment of fig. 8 and 9, the pH adjustment steps S3 and S5 include the 1 st pH adjustment step S3 and the 2 nd pH adjustment step S5, but may be configured to include 3 or more steps or only 1 step depending on the components contained in the waste lithium ion battery.

In the embodiment of fig. 8 and 9, as shown in fig. 11 and 12, a treatment step for removing impurities such as silica contained in the inorganic salt solution may be performed after the dissolution step S12 and before the electrodialysis step S13. This treatment step may be performed in place of the impurity removal step S7 or in addition to the impurity removal step S7.

Specifically, first, in the recrystallization step S12-1, the inorganic salt (sodium chloride in the present embodiment) contained in the inorganic salt solution is recrystallized. The method for recrystallizing the inorganic salt contained in the inorganic salt solution is not particularly limited, and for example, evaporative crystallization using the evaporative crystallization apparatus 13 can be used. Evaporative crystallization crystals of inorganic salts are precipitated by heating an inorganic salt solution to evaporate a solvent and increase the concentration of the inorganic salt. It is to be noted that the evaporation of the inorganic salt solution is preferably performed under a low pressure lower than the atmospheric pressure. In the evaporative crystallization, the inorganic salt contained in the inorganic salt solution may be crystallized by the evaporative concentration apparatus 5 without separately providing the evaporative crystallization apparatus 10.

After the crystals of the inorganic salt are reprecipitated, the crystals of the inorganic salt are separated from the aqueous solution containing the crystals of the inorganic salt in the solid-liquid separation step S12-2, and the recrystallized crystals of the inorganic salt are recovered. As the solid-liquid separation method, for example, various filtration apparatuses such as pressure filtration (filter press), vacuum filtration, and centrifugal filtration, and known solid-liquid separation apparatuses such as a decanter type centrifugal separation apparatus can be used.

Then, in the redissolution step S12-3, the crystals of the recovered inorganic salt are dissolved with, for example, water in the redissolution tank 11 to have a desired concentration, thereby regenerating an inorganic salt solution. The temperature at this time is not particularly limited as long as the temperature is a temperature at which crystals of the inorganic salt can be dissolved. The water used for dissolving the inorganic salt is not particularly limited, but it is preferable to utilize condensed water generated when the liquid to be treated is concentrated by evaporation in the concentration step S8, whereby the condensed water can be effectively utilized. The regenerated inorganic salt solution is supplied to the bipolar membrane electrodialysis device 9. In the recrystallization step S12-1 to the redissolution step S12-3, the impurities removed from the inorganic salt solution may contain calcium and/or magnesium in addition to silica.

In the embodiment of fig. 11 and 12, silica contained in the inorganic salt solution is removed before the electrodialysis step S13. Accordingly, the amount of impurities in the inorganic solution subjected to electrodialysis in the electrodialysis step S13 is also reduced, and thus the performance of the bipolar membrane can be maintained high. Further, when the dilute inorganic salt solution (desalted solution) after the electrodialysis step S13 is supplied to the evaporation concentration apparatus 5 and evaporation concentration is performed again in the concentration step S8, the amount of impurities in the desalted solution is reduced, and generation and adhesion of scale on the heat transfer surface of the heat exchanger of the evaporation concentration apparatus 5 can be suppressed in the concentration step S8. Further, the amount of impurities in the liquid to be treated from which precipitates are separated in the solid-liquid separation step S11 after the carbonation step S10 is reduced, and more liquid to be treated after the solid-liquid separation step S11 can be circulated again in the system. This enables more lithium remaining in the liquid to be treated after the solid-liquid separation step S11 to be recovered, and enables lithium to be recovered at a high recovery rate.

In the embodiment of fig. 8 and 9, as shown in fig. 13 and 14, a firing step S0 of firing the spent lithium ion batteries may be further provided before the acid leaching step S1. In the firing step S0, the method for firing the spent lithium ion battery is not particularly limited, and a known firing apparatus 12 may be used.

In the embodiment shown in fig. 13 and 14, the exhaust gas generated in the baking apparatus 12 (baking step S0) is supplied to the carbonating tank 7, and the exhaust gas is mixed as carbon dioxide into the liquid to be treated in the carbonating step S10. This can reduce the amount of carbon dioxide used in the carbonation step S10. In addition, in the carbonation step S10, the temperature of the treatment target liquid may be increased. It is needless to say that the baking step S0 of baking the spent lithium ion batteries may be performed before the acid leaching step S1 in the embodiment of fig. 11 and 12.

The lithium recovery method of the above embodiment exemplifies a case where lithium is recovered from a waste lithium ion battery, but the lithium recovery method of the present disclosure is not limited to a method for recovering lithium from a waste lithium ion battery.

Cobalt recovery process

From the viewpoint of effective utilization of resources, it is extremely important to recover noble metal-cobalt from spent lithium ion batteries. However, the method for recovering cobalt from a spent lithium ion battery described in patent document 1 in the background art has the following problems: when the pH of the acid leachate is set to 4 or more in order to remove the impurity metals such as aluminum from the acid leachate, crystals of the cobalt salt are precipitated and precipitated together with crystals of the salt of the impurity metal, and cobalt is removed from the acid leachate together with the impurity metals, and then the recovery rate of cobalt may be lowered when cobalt is recovered.

In order to solve the above problems, an object of the present disclosure is to provide a cobalt recovery method capable of recovering cobalt from a treatment target solution in which cobalt and impurity metals are dissolved, at a high recovery rate.

As a result of intensive studies to solve the above problems, the present inventors have found that, when a solution to be treated containing at least cobalt and an impurity metal dissolved therein is adjusted in pH to precipitate a salt of the impurity metal as crystals, if the concentration of an aqueous solution of an alkali added to the solution to be treated is high, the crystals of the cobalt salt precipitate together with the crystals of the salt of the impurity metal, and cobalt is removed together with the impurity metal from the solution to be treated. Based on such findings and further repeated studies, the cobalt recovery method of the present disclosure was completed as a result. Namely, the present disclosure provides a cobalt recovery method in the following manner.

The disclosed cobalt recovery method is characterized by comprising the following steps: a pH adjustment step (1) of adding an aqueous alkali solution to an acidic treatment target solution in which at least cobalt and an impurity metal are dissolved to adjust the pH to 4 to 7, thereby precipitating a salt of the impurity metal as crystals; a first solid-liquid separation step of separating a precipitate containing crystals of a salt of an impurity metal precipitated in the first pH adjustment step 1 from a liquid to be treated; a 2 nd pH adjustment step of adding an aqueous alkali solution to the liquid to be treated after the 1 st solid-liquid separation step to adjust the pH to 7 or more, thereby precipitating crystals of a cobalt salt; and a 2 nd solid-liquid separation step of separating a precipitate containing crystals of a cobalt salt precipitated in the 2 nd pH adjustment step from the liquid to be treated, wherein the alkali concentration of the aqueous solution of the alkali added in the 1 st pH adjustment step is less than 1.0 mol/L.

In the cobalt recovery method according to paragraph 0163, the alkali concentration of the aqueous solution of the alkali added in the above-mentioned pH adjustment step 1 is preferably 0.1mol/L or more.

In addition, in the cobalt recovery method described in paragraph 0163 or 0164, it is preferable that: in the first pH adjustment step 1, an aqueous solution of an alkali having an alkali concentration of 1.0mol/L or more is added to the liquid to be treated so that the pH of the liquid to be treated becomes a predetermined value of less than 4, and then an aqueous solution of an alkali having an alkali concentration of less than 1.0mol/L is added to the liquid to be treated so that the pH of the liquid to be treated is adjusted to 4 to 7.

In the cobalt recovery method according to any one of paragraphs 0163 to 0165, lithium is dissolved in the treatment liquid, and the method preferably comprises: a concentration step of evaporating and concentrating the liquid to be treated after the 2 nd solid-liquid separation step; and a carbonation step of mixing carbon dioxide and/or adding a water-soluble carbonate to the liquid to be treated after the concentration step.

In addition, the cobalt recovery method described in paragraph 0166 preferably further comprises: a 3 rd solid-liquid separation step of separating precipitates containing crystals of lithium carbonate precipitated in the carbonation step from the liquid to be treated; and an electrodialysis step of separating and recovering an alkali from the treatment target liquid by performing bipolar membrane electrodialysis on the treatment target liquid after the 3 rd solid-liquid separation step, and reusing the alkali recovered in the electrodialysis step as an alkali used in the 1 st pH adjustment step and/or the 2 nd pH adjustment step.

According to the cobalt recovery method of the present disclosure, when removing impurity metals from a treatment target solution in which cobalt and impurity metals are dissolved in the 1 st pH adjustment step, the pH of the treatment target solution is adjusted using a dilute alkali aqueous solution having an alkali concentration of less than 1.0mol/L, whereby the removal of cobalt together with the impurity metals from the treatment target solution can be suppressed. This can maintain the amount of cobalt in the liquid to be treated supplied to the 2 nd pH adjustment step high, and thus cobalt can be recovered at a high recovery rate in the 2 nd pH adjustment step.

Fig. 15 shows steps of respective steps relating to an embodiment of the cobalt recovery method of the present disclosure, and fig. 16 shows a schematic configuration of a treatment apparatus 10 for implementing the cobalt recovery method of fig. 15. The cobalt recovery method of the present embodiment will be described by taking as an example a case where lithium is recovered in addition to cobalt from a spent lithium ion battery.

The cobalt recovery method of the present embodiment includes:

an acid leaching step S1 of leaching the spent lithium ion battery with an inorganic acid to leach out cobalt and lithium;

a solid-liquid separation step S2 of separating an insoluble residue from the liquid to be treated obtained in the acid leaching step S1;

a 1 st pH adjustment step S3 of adjusting the pH to 4 to 7 by adding an aqueous alkali solution to the liquid to be treated after the solid-liquid separation step S2;

a solid-liquid separation step S4 (corresponding to the "1 st solid-liquid separation step" in paragraph 0163) of separating a precipitate containing crystals of a salt of an impurity metal precipitated in the first pH adjustment step S3 from the liquid to be treated;

a pH 2 adjustment step S5 of adjusting the pH to 7 or more by adding an aqueous alkali solution to the liquid to be treated after the solid-liquid separation step S4;

a solid-liquid separation step S6 (corresponding to the "2 nd solid-liquid separation step" in paragraph 0163) of separating a precipitate containing crystals of a cobalt salt precipitated in the pH 2 adjustment step S5 from the liquid to be treated;

a concentration step S7 of 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 "3 rd solid-liquid separation step" in paragraph 0167) of separating a precipitate containing crystals of lithium carbonate precipitated in the carbonation step S8 from the liquid to be treated; and

an electrodialysis step S10 of separating and recovering an alkali containing at least lithium hydroxide and an inorganic acid from the treatment target liquid after the solid-liquid separation step S9 by performing bipolar membrane electrodialysis on the treatment target liquid.

The waste lithium ion battery to be recovered is the same as in the above-described lithium recovery method.

First, in the acid leaching step S1, the spent lithium ion battery is leached with an inorganic acid, whereby cobalt, lithium, and metals such as aluminum, nickel, and iron are eluted. As the inorganic acid, for example, sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, or the like can be used, and in the present embodiment, sulfuric acid is used from the viewpoint of low cost and easy handling.

In the acid leaching step S1, the method of leaching the spent lithium ion battery with the inorganic acid is not particularly limited, and a commonly used method can be used. For example, the acid leaching tank 1 is used to immerse the spent lithium ion battery in an aqueous solution of an inorganic acid such as an aqueous solution of sulfuric acid, and the spent lithium ion battery is stirred for a predetermined time to obtain an acidic solution to be treated in which the above-mentioned metal such as cobalt is dissolved. In the acid leaching step S1, the concentration of the inorganic acid in the aqueous solution is preferably 1mol to 5mol/L, and the temperature of the aqueous solution is preferably 60 ℃ or higher.

In the subsequent solid-liquid separation step S2, the liquid to be treated obtained in the acid leaching step S1 is filtered, for example, to separate an insoluble residue from the liquid to be treated. The insoluble residue is mainly a carbon material, a metal material, or an organic material insoluble in an inorganic acid. As a method for performing solid-liquid separation, for example, various filtration apparatuses such as pressure filtration (filter press), vacuum filtration, and centrifugal filtration, and known solid-liquid separation apparatuses such as centrifugal separation apparatuses of a decanter type can be used. The same applies to the following solid-liquid separation steps S4, S6, S9, and the like.

In the following pH adjustment step S3, an aqueous alkali solution is added to the liquid to be treated (filtrate) after the solid-liquid separation step S2 to adjust the pH to 4 to 7, preferably 4 to 6, more preferably 4 to 5. Thereby, impurity metals (e.g., aluminum and iron) among the metals in the liquid to be treated are removed from the liquid to be treated. As the base, sodium hydroxide, potassium hydroxide, lithium hydroxide, or the like can be used, and lithium hydroxide is used in the present embodiment.

In the 1 st pH adjustment step S3, the method for adjusting the pH of the liquid to be treated is not particularly limited, and a commonly performed method can be used. For example, by adding an aqueous alkali solution such as an aqueous lithium hydroxide solution while stirring the liquid to be treated in the pH adjustment tank 12, the impurity metals in the liquid to be treated are precipitated and precipitated in the form of crystals of inorganic salts such as hydroxides (for example, aluminum hydroxide and iron hydroxide). In the 1 st pH adjustment step S3, the treatment solution is preferably heated to a constant temperature of, for example, 30 to 80 ℃.

The aqueous solution of the alkali added in the pH adjustment step S3 at 1 st is relatively dilute and has an alkali concentration of less than 1.0 mol/L. As a result, although described in detail later, in the pH adjustment step S3 1, the precipitation, and removal of cobalt in the liquid to be treated as a cobalt salt together with the impurity metal can be suppressed. However, if the alkali concentration is too low, the lower limit of the alkali concentration is preferably 0.1mol/L or more because it is necessary to use a large amount of an alkali aqueous solution to adjust the pH in the 1 st pH adjustment step S3 and the amount of liquid of the liquid to be treated after pH adjustment increases. In addition, in order to effectively suppress the removal of cobalt in the treatment target liquid from the treatment target liquid in the 1 st pH adjustment step S3, the alkali concentration of the aqueous solution of the alkali added in the 1 st pH adjustment step S3 is preferably 0.5mol/L or less, and more preferably 0.2mol/L or less.

In the 1 st pH adjustment step S3, in order to reduce the amount of the aqueous solution of the alkali used for pH adjustment, 1.0mol/L or more of an aqueous solution of an alkali having a high alkali concentration may be added to the liquid to be treated to a predetermined value at which the pH of the liquid to be treated is less than 4, and after the pH of the liquid to be treated reaches the predetermined value, less than 1.0mol/L of an aqueous solution of an alkali having a low alkali concentration may be added to the liquid to be treated, thereby adjusting the pH of the liquid to 4 to 7. The predetermined value of the pH of the liquid to be treated may be set within a range of 2 to 3.

The precipitate precipitated in the pH 1 adjustment step S3 is separated from the liquid to be treated by, for example, filtration in the subsequent solid-liquid separation step S4. The impurity metal removed from the treatment liquid in the pH adjustment step S3 1 may contain copper or the like. In the solid-liquid separation step S4, it is preferable to wash the precipitate with a washing liquid and supply the washed waste washing liquid to the next pH adjustment step S5 together with the liquid to be treated (filtrate). Thus, lithium contained in the waste cleaning liquid may be supplied from the pH 2 adjustment step S5 to the carbonation step S8 together with lithium contained in the liquid to be treated, and the lithium may be recovered at a high recovery rate by performing carbonation in the carbonation step S8 described later. The water used for washing the precipitates is not particularly limited, but is preferably condensed water generated when the liquid to be treated is concentrated by evaporation in the concentration step S7 described later, whereby the condensed water can be effectively used.

In the pH 2 adjustment step S5, an aqueous alkali solution is added to the liquid to be treated (filtrate) after the solid-liquid separation step S4 to adjust the pH to 7 or more, preferably 7 to 13, more preferably 7 to 11, and still more preferably 8 to 10. In this way, cobalt, nickel, and other noble metals in the treatment liquid are removed from the treatment liquid. As the base, sodium hydroxide, potassium hydroxide, lithium hydroxide, or the like can be used, and lithium hydroxide is used in the present embodiment.

In the pH adjustment step S5, the method for adjusting the pH of the liquid to be treated is not particularly limited, and a commonly-performed method can be used. For example, the noble metal in the liquid to be treated is precipitated and precipitated in the form of crystals of an inorganic salt such as a hydroxide (for example, iron cobalt hydroxide and nickel hydroxide) by adding an aqueous alkali solution such as an aqueous lithium hydroxide solution while stirring the liquid to be treated in the pH adjustment tank 2 3. Thus, cobalt in the treatment liquid can be recovered as a cobalt salt such as cobalt hydroxide. In the pH 2 adjustment step S5, the treatment solution is preferably heated to a constant temperature of, for example, 30 to 80 ℃. The alkali concentration of the aqueous alkali solution to be added in the 2 nd pH adjustment step S5 is not particularly limited, but is preferably equal to or higher than the alkali concentration of the aqueous alkali solution used in the 1 st pH adjustment step S3, and more preferably 0.2mol/L or higher.

The precipitate precipitated and precipitated in the pH 2 adjustment step S5 is separated from the liquid to be treated in the subsequent solid-liquid separation step S6 by, for example, filtration of the liquid to be treated. The precious metal removed from the treatment liquid in the pH 2 adjustment step S5 may further include manganese or the like. On the other hand, the liquid to be treated (filtrate) after the solid-liquid separation step S6 contains lithium and anions of an inorganic acid (for example, sulfate ions).

In the solid-liquid separation step S6, it is preferable to wash the precipitate with a cleaning liquid and supply the washed waste cleaning liquid to the subsequent concentration step S7 together with the liquid to be treated (filtrate). Thus, lithium contained in the waste cleaning liquid can be supplied from the concentration step S7 to the carbonation step S8 together with lithium contained in the liquid to be treated, and the lithium can be recovered at a high recovery rate by carbonation in the carbonation step S8 described later. The water used for washing the precipitates is not particularly limited, and it is preferable to use condensed water generated when the liquid to be treated is concentrated by evaporation in the concentration step S7, whereby the condensed water can be effectively used.

In the 1 st pH adjustment step S3 and the 2 nd pH adjustment step S5, the alkali used is lithium hydroxide, whereby it is possible to suppress the contamination of alkali metals other than lithium, such as sodium, into the crystals of lithium carbonate precipitated in the carbonation step S8, which will be described later, as compared with the case of using hydroxides of other alkali metals, such as sodium hydroxide. Thereby, lithium carbonate having high purity can be recovered.

In the next concentration step S7, the lithium-containing liquid to be treated after the solid-liquid separation step S6 is heated and evaporated, and the liquid to be treated is concentrated by evaporating water in the liquid to be treated. This reduces the amount of liquid in the treatment target liquid and increases the lithium concentration in the treatment target liquid. This can improve the recovery rate of lithium carbonate in the carbonation step S8 described later.

In the concentration step S7, the temperature of the concentrated liquid to be treated can be increased by evaporating and concentrating the liquid to be treated, and the recovery rate of lithium carbonate can be increased in the carbonation step S8 described later. Since the solubility of lithium carbonate decreases as the temperature increases, the solubility of lithium carbonate generated by the reaction between lithium and carbon dioxide in the liquid to be treated decreases as the temperature of the liquid to be treated increases in the carbonation step S8, and therefore the amount of precipitated lithium carbonate crystals can be increased.

In the concentration step S7, the liquid to be treated is preferably concentrated to a concentration at which lithium is not precipitated in the concentrated liquid to be treated, for example, in the form of crystals of a lithium salt such as lithium sulfate. This can increase the lithium concentration in the concentrated liquid to be treated, and the recovery rate of lithium carbonate can be increased in the carbonation step S8 described later. When the precipitate is precipitated in the concentration step S7, a solid-liquid separation step of separating the precipitate from the liquid to be treated may be performed.

In the concentration step S7, the method of evaporating and concentrating the liquid to be treated is not particularly limited, and, for example, the evaporation and concentration apparatus 5 can be used. The evaporation concentration device 5 is not particularly limited as long as it can concentrate the liquid to be treated by evaporation, and known evaporation concentration devices such as a heat pump type, an ejector (injector) type, a steam type, and a flash evaporation type can be used. When the heat pump type evaporation and concentration apparatus is used, the energy used can be significantly suppressed. Further, energy saving can be achieved by concentrating the treatment target liquid under a reduced pressure atmosphere.

In the subsequent carbonation step S8, carbon dioxide and/or a water-soluble carbonate is added to the liquid to be treated after the concentration step S7, whereby lithium in the liquid to be treated is precipitated and precipitated as lithium carbonate crystals. Thus, lithium in the treatment liquid can be recovered as lithium carbonate. As the carbonate, for example, sodium carbonate, ammonium carbonate, potassium carbonate, or the like can be used.

In the carbonation step S8, carbon dioxide is preferably mixed with the liquid to be treated to precipitate and precipitate crystals of lithium carbonate. Thus, in the carbonation step S8, the use of a material containing no alkali metal such as sodium makes it possible to suppress the alkali metal other than lithium from being mixed into the precipitated lithium carbonate crystals. Thereby, lithium carbonate having high purity can be recovered.

In the carbonation step S8, the method of mixing carbon dioxide into the liquid to be treated is not particularly limited, and a commonly performed method can be used. For example, carbon dioxide can be supplied to the liquid to be treated in the form of fine bubbles by a nozzle while stirring the liquid to be treated in the carbonation tank 7, whereby carbon dioxide can be uniformly mixed with the liquid to be treated, and lithium in the liquid to be treated can be efficiently reacted with carbon dioxide. Alternatively, the reaction with carbon dioxide may be carried out by spraying the liquid to be treated in a carbon dioxide atmosphere.

Since the solubility of lithium carbonate decreases as the temperature increases, the temperature of the treatment liquid is preferably increased in the carbonation step S8. This reduces the solubility of lithium carbonate generated by the reaction between lithium and carbon dioxide in the liquid to be treated, and can increase the amount of lithium carbonate crystals precipitated.

In the subsequent solid-liquid separation step S9, the liquid to be treated after the carbonation step S8 is filtered, for example, to separate a precipitate containing crystals of lithium carbonate from the liquid to be treated. In the solid-liquid separation step S9, impurities can be removed and the purity of lithium carbonate can be improved by washing the precipitate separated from the liquid to be treated with water or the like. The water used for washing the precipitates is not particularly limited, and it is preferable to use condensed water generated when the liquid to be treated is concentrated by evaporation in the concentration step S7, whereby the condensed water can be effectively used. It is preferable that the washing waste liquid after washing the precipitate is supplied to the bipolar membrane electrodialysis device 6 of 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 subsequent electrodialysis step S10, the treatment target liquid after the solid-liquid separation step S9 is supplied to the bipolar membrane electrodialysis device 6, whereby the alkali and the inorganic acid are separated and recovered from the treatment target liquid. As the bipolar membrane electrodialysis device 9, for example, a bipolar membrane electrodialysis device of a three-compartment cell system shown in fig. 17, in which a plurality of cells 90 are laminated, and the cells 90 include an anion exchange membrane 91, a

cation exchange membrane

92, and 2

bipolar membranes

In the electrodialysis step S10, the liquid to be treated is introduced into the desalting chamber R1, and pure water is introduced into the acid chamber R2 and the alkali chamber R3, respectively. Thus, when the liquid to be treated contains lithium and an anion of an inorganic acid (sulfate ion in the present embodiment), lithium ions (Li ions) are present in the desalination chamber R1⁺) Passing through cation exchange membrane 92, sulfate ion (SO)₄ ^2-) Through an 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) in the bipolar membranes 93 and 94⁺) And hydroxide ion (OH)^-) Hydrogen ion (H) in acid compartment R2⁺) With sulfate ions (SO)₄ ^2-) Combine to form sulfuric acid (H)₂SO₄) In the base chamber R3, hydroxide ion (OH)^-) With lithium ions (Li)⁺) Binding to form lithium hydroxide (LiOH). Thus, sulfuric acid (H) as an inorganic acid was recovered from the acid chamber R2₂SO₄) Lithium hydroxide (LiOH) as a base was recovered from the base chamber R3. The pure water introduced into the acid chamber R2 and the alkali chamber R3 can be condensed water generated when the liquid to be treated is concentrated by evaporation in the concentration step S7.

Although the desalted dilute treatment liquid (desalted liquid) discharged from the desalting chamber R1 is not particularly limited, it is preferable that at least a part of the desalted dilute treatment liquid (desalted liquid) contains a small amount of lithium and is supplied to the concentration step S7 (evaporation and concentration apparatus 5) or an impurity removal step (polyvalent cation removal apparatus) before the concentration step S7 described later, concentrated again in the concentration step S7, and then carbonated in the carbonation step S8. Thus, lithium can be recovered at a high recovery rate. In the present embodiment, the desalted liquid is supplied to the concentration step S7, but may be supplied to the 1 st pH adjustment step S3. Thus, when cobalt remains in the desalted liquid, the recovery rate of cobalt can be improved.

Although the inorganic acid (sulfuric acid in the present embodiment) recovered from the acid chamber R2 is not particularly limited, it is preferably supplied to the acid leaching tank 1 and reused as the inorganic acid for leaching the spent lithium ion battery in the acid leaching step S1.

The alkali (lithium hydroxide in the present embodiment) recovered from the alkali chamber R3 is not particularly limited, but is preferably supplied to the

pH adjustment tanks

2 and 3 and reused as an alkali for adjusting the pH of the liquid to be treated in the pH adjustment steps S3 and S5.

According to the cobalt recovery method of the present embodiment described above, when removing impurity metals from a treatment target solution in which cobalt and impurity metals are dissolved in the 1 st pH adjustment step S3, the pH of the treatment target solution is adjusted with a dilute aqueous alkali solution having an alkali concentration of less than 1.0mol/L, thereby suppressing removal of cobalt together with the impurity metals from the treatment target solution. Thus, the amount of cobalt in the liquid to be treated supplied to the 2 nd pH adjustment step S5 can be maintained high, and therefore cobalt can be recovered at a high recovery rate in the 2 nd pH adjustment step S5.

In addition, according to the cobalt recovery method of the present embodiment, since a dilute aqueous alkali solution having an alkali concentration of less than 1.0mol/L is used in the 1 st pH adjustment step S3, the amount of liquid to be supplied to the liquid to be treated in the subsequent carbonation step S8 for lithium recovery increases, but the amount of liquid in the liquid to be treated is reduced by performing evaporation and concentration on the liquid to be treated in the concentration step S7 before the carbonation step S8. The lithium concentration in the liquid to be treated is increased. This can improve the recovery rate of lithium carbonate in the carbonation step S8. Further, since the temperature of the liquid to be treated supplied to the carbonation step S8 increases as the liquid to be treated is evaporated and concentrated, the solubility of lithium carbonate decreases, and the amount of precipitated lithium carbonate can be increased.

In the 1 st pH adjustment step S3, when adjusting the pH of the liquid to be treated to 4 to 7, the amount of the aqueous alkali solution used for pH adjustment may be reduced by adding an aqueous alkali solution having an alkali concentration of 1.0mol/L or more to the liquid to be treated until the pH of the liquid to be treated reaches a predetermined value, and adding an aqueous alkali solution having an alkali concentration of less than 1.0mol/L to the liquid to be treated after the pH of the liquid to be treated reaches the predetermined value.

In addition, according to the cobalt recovery method of the present embodiment, the amount of the inorganic acid and the alkali used in the steps S1, S3, and S5 can be reduced by recycling the inorganic acid and the alkali recovered in the electrodialysis step S10 to the acid leaching step S1 and the pH adjustment steps S3 and S5, respectively, and reusing them.

Although one embodiment of the cobalt recovery method of the present disclosure has been described above, the cobalt recovery method of the present disclosure is not limited to the embodiment of fig. 15 and 16, and various modifications may be made without departing from the scope of the present disclosure.

For example, in the embodiment of fig. 15 and 16, the alkali recovered in the electrodialysis step S10 is supplied to the 1 st pH adjustment step S3 and the 2 nd pH adjustment step S5, but may be supplied only to either step.

In the embodiment of fig. 15 and 16, at least a part of the dilute treatment liquid (desalted liquid) from which lithium hydroxide has been recovered in the electrodialysis step S10 is supplied to the concentration step S7, but may be supplied to the electrodialysis step S10 instead of or in addition to this step.

In the embodiment of fig. 15 and 16, the concentration step S7 is provided before the carbonation step S8, but the concentration step S7 is not necessarily provided. In this case, the following configuration is possible: at least a part of the dilute treatment liquid (desalted liquid) from which lithium hydroxide has been recovered in the electrodialysis step S10 is supplied to the carbonation step S8.

In addition, the embodiment of fig. 15 and 16 may be configured in the following manner: impurities of polyvalent cations (typically calcium ions and magnesium ions) having a valence of 2 or more in the liquid to be treated before the concentration step S7 and/or the liquid to be treated supplied to the electrodialysis step S10 are removed. If multivalent cations such as calcium ions and magnesium ions are present in the treatment target liquid, there is a concern that the multivalent cations will precipitate in the cation exchange membrane of the bipolar membrane electrodialysis device 9, resulting in a decrease in the performance of the membrane, and by removing the multivalent cations from the treatment target liquid in advance, adverse effects on the cation exchange membrane of the bipolar membrane electrodialysis device 9 can be prevented. The specific embodiment for removing the polyvalent cation is not particularly limited, and for example, a known polyvalent cation removing apparatus capable of introducing a treatment target solution into a column packed with a chelating resin can be exemplified. As the chelate resin, a chelate resin capable of selectively capturing calcium ions and magnesium ions can be used, and examples thereof include iminodiacetic acid type and aminophosphonic acid type. Examples of the polyvalent cation removing device include those to which a chelating agent is added and those using an ion exchange resin. The impurities removed from the treatment liquid may contain silicon dioxide (silicate ions) in addition to calcium and magnesium.

In the embodiment shown in fig. 15 and 16, as shown in fig. 18 and 19, a firing step S0 of firing the spent lithium ion batteries may be further provided before the acid leaching step S1. In the firing step S0, the method for firing the spent lithium ion battery is not particularly limited, and a known firing apparatus 12 may be used.

In the embodiment shown in fig. 18 and 19, the exhaust gas generated in the baking apparatus 12 (baking step S0) is supplied to the carbonating tank 7 (carbonation step S8) and mixed as carbon dioxide into the liquid to be treated. This can reduce the amount of carbon dioxide used in the carbonation step S8.

In the embodiment of fig. 15 and 16, the method for recovering lithium in the steps after the concentration step S7 is not particularly limited, and may be the method for recovering lithium of the present disclosure described above. In the lithium recovery method according to the above embodiment, the cobalt recovery method of the present disclosure is used in the acid leaching step S1 to the solid-liquid separation step S6.

In addition, the cobalt recovery method of the above embodiment exemplifies a case where cobalt is recovered from a waste lithium ion battery, but the cobalt recovery method of the present disclosure is not limited to a method for recovering cobalt from a waste lithium ion battery.

Test examples

The present inventors conducted the following test with respect to the alkali concentration of the aqueous solution of the alkali added in the pH 1 adjustment step S3. Specifically, the following treatments were performed: the pH of the liquid to be treated was adjusted by adding an aqueous alkali solution to 200ml of the liquid to be treated having the components shown in table 1 below (pH 1 adjustment step S3). As the aqueous solution of the alkali to be added, an aqueous lithium hydroxide solution is used. The alkali concentration of the lithium hydroxide aqueous solution was set to 0.2mol/L (example 1), 0.5mol/L (example 2), and 1.0mol/L (example 3), and the amount of the lithium hydroxide aqueous solution added was adjusted so that the pH of the treatment liquid became 4.7. The amount of the aqueous lithium hydroxide solution added was 418.6ml in example 1, 168.5ml in example 2, and 86.3ml in example 3. By adding the lithium hydroxide aqueous solution, the lithium content in the treatment target solution was 582mg in example 1, 585mg in example 2, and 599mg in example 3, which were further increased.

[ Table 1]

Then, the pH-adjusted liquid to be treated was filtered through a filter paper, and the content of each component contained in the filtrate obtained by the filtration was measured. The results are shown in Table 2.

[ Table 2]

On the other hand, the surface state of the filtration residue obtained by filtration of the pH-adjusted liquid to be treated was confirmed. The results are shown in fig. 20 to 22. Fig. 20 shows embodiment 1, fig. 21 shows embodiment 2, and fig. 22 shows embodiment 3. In fig. 22, it was visually confirmed that cobalt hydroxide was contained in the filtration residue of example 3, whereas in fig. 20 and 21, it was visually confirmed that cobalt hydroxide was not contained in the filtration residues of examples 1 and 2.

From the above results, it can be confirmed from fig. 20 to 22 that: when the alkali concentration of the aqueous solution of the alkali added to the liquid to be treated in the 1 st pH adjustment step S3 is 1.0mol/L, the liquid to be treated is pH-adjusted and the filtration residue contains a large amount of cobalt salt. Further, from table 2, it was confirmed that a large amount of cobalt remained in the liquid to be treated (filtrate) when the alkali concentration of the alkali aqueous solution added to the liquid to be treated in the 1 st pH adjustment step S3 was 1.0mol/L, the cobalt recovery rate of the liquid to be treated (filtrate) after pH adjustment was less than 85%, and when the alkali concentration was less than 1.0mol/L, the cobalt recovery rate of the liquid to be treated (filtrate) after pH adjustment was 85% or more.

Thus, by setting the alkali concentration of the alkali aqueous solution added to the liquid to be treated in the 1 st pH adjustment step S3 to less than 1.0mol/L, it is possible to suppress cobalt from being removed from the liquid to be treated together with an impurity metal (for example, aluminum) in the 1 st pH adjustment step S3, and it is possible to maintain the cobalt content in the liquid to be treated supplied to the subsequent 2 nd pH adjustment step S5 high. Thus, cobalt can be recovered at a high recovery rate in the pH adjustment step 2S 5.

Description of the reference numerals

S0 baking step

S1 acid leaching step

S3 pH 1 adjustment step (pH adjustment step)

S5 pH 2 adjustment step (pH adjustment step)

S7 impurity removal step

S8 concentration step

S9 crystallization step

S10 Process for solid-liquid separation (No. 1 solid-liquid separation Process)

S11 carbonation Process

S12 Process for solid-liquid separation (2 nd Process for solid-liquid separation)

S13 dissolving step

S13-1 recrystallization step

S13-3 redissolution step

S14 electrodialysis step.

Claims

1. A lithium recovery method comprising the steps of:

a concentration step of evaporating and concentrating a liquid to be treated in which at least lithium and an inorganic salt are dissolved;

a crystallization step of cooling and crystallizing the liquid to be treated after the concentration step to precipitate inorganic salts in the form of crystals;

a first solid-liquid separation step of separating a precipitate containing crystals of an inorganic salt from the liquid to be treated after the crystallization step;

a carbonation step of mixing carbon dioxide and/or adding a water-soluble carbonate to the liquid to be treated after the 1 st solid-liquid separation step; and the combination of (a) and (b),

and a 2 nd solid-liquid separation step of separating a precipitate containing crystals of lithium carbonate precipitated in the carbonation step from the liquid to be treated.

2. The lithium recovery method according to claim 1, wherein at least a part of the liquid to be treated after the 2 nd solid-liquid separation step is concentrated by evaporation in the concentration step.

3. The lithium recovery method according to claim 1 or 2, further comprising the steps of:

a dissolving step of dissolving an inorganic salt contained as crystals in the precipitate separated from the liquid to be treated in the first solid-liquid separation step 1 to generate an inorganic salt solution; and the combination of (a) and (b),

and an electrodialysis step of subjecting the inorganic salt solution obtained in the dissolving step to bipolar membrane electrodialysis to separate and recover the inorganic acid from the inorganic salt solution together with the alkali.

4. The lithium recovery method according to claim 3, wherein the concentration step is a step of subjecting the inorganic salt solution desalted by the bipolar membrane electrodialysis to evaporation concentration.

5. The lithium recovery method according to any one of claims 1 to 4, further comprising, before the concentration step, the step of:

an acid leaching step of leaching the waste lithium ion battery with an inorganic acid to leach out lithium;

a pH adjustment step of adjusting the pH by adding a base to the lithium-containing liquid obtained in the acid leaching step,

the precipitate precipitated in the pH adjustment step is separated from the lithium-containing liquid, thereby producing a liquid to be treated.

6. The lithium recovery method according to claim 5, wherein at least a part of the liquid to be treated after the 2 nd solid-liquid separation step is reused as the alkali added in the pH adjustment step.

7. The lithium recovery method according to claim 5 or 6, which is recited in claim 3, wherein the base recovered in the electrodialysis step is reused as the base added in the pH adjustment step, and the inorganic acid recovered in the electrodialysis step is reused as the inorganic acid used in the acid leaching step.