CN115244195A

CN115244195A - Cobalt recovery process

Info

Publication number: CN115244195A
Application number: CN202180020176.1A
Authority: CN
Inventors: 三保庆明; 竹内高穗; 平野悟; 横山佳帆; 石田和彦
Original assignee: Sasakura Engineering Co Ltd
Current assignee: Sasakura Engineering Co Ltd
Priority date: 2020-03-09
Filing date: 2021-02-10
Publication date: 2022-10-25
Also published as: WO2021181997A1; KR20220149691A

Abstract

Cobalt is recovered from a liquid to be treated in which cobalt and impurity metals are dissolved at high purity. In the cobalt recovery method, the pH is adjusted to 4 or more and 7 or less by adding an alkali to the liquid to be treated (step S3); performing solid-liquid separation on the precipitate containing the crystals of the salt of the impurity metal precipitated in step S3 (step S4); adjusting the pH to 7 or higher by adding an alkali to the liquid to be treated after the step S4 (step S5); performing solid-liquid separation on the precipitate containing the crystal of the cobalt salt precipitated in the step S5 (step S6); dissolving the precipitate obtained after step S6 with an inorganic acid (step S7-1); adjusting the pH to 4 or more and 7 or less by adding an alkali to the redissolution (step S7-2); precipitating the precipitate containing the crystals of the impurity metal salt precipitated in step S7-2 by its own weight or centrifugal separation, and separating the precipitate into a supernatant and a slurry containing the precipitate (step S7-3); adjusting the pH to 7 or more by adding an alkali to the redissolution as a supernatant after the step S7-3 (step S7-4); the precipitate containing the crystal of the cobalt salt precipitated in the step S7-4 is subjected to solid-liquid separation (step S7-5).

Description

Cobalt recovery process

Technical Field

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

Background

Lithium ion batteries have attracted attention as lightweight batteries with high energy density, and are widely used as 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 is used as a positive electrode active material, and from the viewpoint of effective utilization of resources, it is extremely important to recover valuable metal cobalt from waste lithium ion batteries.

As a method for recovering cobalt from a spent lithium ion battery, the following methods have been conventionally performed: and leaching the waste lithium ion battery by using acid to dissolve cobalt, and separating and recovering the cobalt from the treated liquid in which the cobalt is dissolved.

However, the spent lithium ion batteries contain impurity metals such as iron, aluminum, and copper, and these impurity metals are dissolved in the treatment liquid by acid leaching, whereby the impurity metals are mixed into cobalt, which is a target recovery product, and the quality is degraded.

Disclosure of Invention

Problems to be solved by the invention

An object of the present disclosure is to provide a cobalt recovery method capable of recovering cobalt with high purity from a liquid to be treated in which at least cobalt and an impurity metal are dissolved.

Means for solving the problems

A cobalt recovery method according to an aspect of the present disclosure is characterized by including the steps of: a primary low-pH adjustment step of adding an alkali to an acidic treatment target solution in which at least cobalt and impurity metals are dissolved to adjust the pH to 4 or more and 7 or less; a primary impurity metal separation step of separating a precipitate containing crystals of a salt of an impurity metal precipitated in the primary low pH adjustment step from a liquid to be treated by using a solid-liquid separator; a primary high pH adjustment step of adjusting the pH to 7 or more by adding an alkali to the liquid to be treated after the primary impurity metal separation step; a primary cobalt separation step of separating a precipitate containing crystals of a cobalt salt precipitated in the primary high pH adjustment step from a liquid to be treated by using a solid-liquid separator; a re-dissolving step of adding an inorganic acid to dissolve the precipitate separated in the primary cobalt separation step, thereby producing a re-dissolved solution; a secondary low pH adjustment step of adjusting the pH to 4 or more and 7 or less by adding an alkali to the redissolved solution; a secondary impurity metal separation step of precipitating a precipitate containing crystals of the impurity metal salt precipitated in the secondary low pH adjustment step by its own weight or centrifugal separation, and separating the precipitate into a supernatant liquid and a slurry containing the precipitate; a secondary high pH adjustment step of adjusting the pH to 7 or more by adding an alkali to the redissolved solution as a supernatant after the secondary impurity metal separation step; and a secondary cobalt separation step of recovering a precipitate containing crystals of a cobalt salt precipitated in the secondary high pH adjustment step from the redissolved solution by using a solid-liquid separation apparatus.

According to the cobalt recovery method of one aspect of the present disclosure, the impurity metals are removed from the liquid to be treated by first adjusting the pH of the liquid to be treated, in which at least cobalt and impurity metals are dissolved, to 4 or more and 7 or less by adding an alkali in the first low pH adjustment step, and by adjusting the pH of the liquid to 7 or more by adding an alkali in the first high pH adjustment step, cobalt contained in the liquid to be treated is precipitated as a cobalt salt. Then, the precipitated cobalt salt is dissolved with an inorganic acid in the redissolution step, and the pH of the redissolution is adjusted to 4 or more and 7 or less by adding an alkali in the secondary low pH adjustment step, whereby the residual impurity metal can be removed from the redissolution even if the salt of the impurity metal remaining in the liquid to be treated is simultaneously precipitated and mixed in with the cobalt salt precipitated in the primary high pH adjustment step. Further, the pH of the redissolution from which the impurity metals have been removed is adjusted to 7 or more by adding an alkali to the redissolution in the secondary high pH adjustment step, and cobalt contained in the liquid to be treated can be recovered with high purity by precipitating as a cobalt salt.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the cobalt recovery method of the present disclosure, cobalt can be recovered with high purity from a liquid to be treated in which cobalt and impurity metals are dissolved.

Drawings

Fig. 1 is a flow chart showing the steps of the cobalt recovery method of the first embodiment.

Fig. 2 is a flowchart showing steps of a method for recovering lithium contained in a liquid to be treated.

Fig. 3 is a schematic diagram showing a schematic configuration of a processing apparatus used in the cobalt recovery method shown in fig. 1.

Fig. 4 is a schematic diagram showing a schematic configuration of a processing apparatus used in the lithium recovery method shown in fig. 2.

Fig. 5 is a schematic diagram showing a schematic configuration of the bipolar membrane electrodialysis device.

FIG. 6 is a photograph showing the surface state of the filtration residue of example 1.

FIG. 7 is a photograph showing the surface state of the filtered residue of example 2.

FIG. 8 is a photograph showing the surface state of the filtered residue of example 3.

Fig. 9 is a flowchart schematically showing steps of a variation of the cobalt recovery method according to the first embodiment.

Fig. 10 is a schematic diagram showing a schematic configuration of a processing apparatus used in the cobalt recovery method shown in fig. 9.

Fig. 11 is a flowchart schematically showing steps of a variation of the cobalt recovery method according to the first embodiment.

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

Fig. 13 is a flowchart schematically showing steps of a variation of the cobalt recovery method according to the first embodiment.

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

Fig. 15 is a flowchart schematically showing steps of a variation of the cobalt recovery method according to the first embodiment.

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

Fig. 17 is a flowchart showing steps of a cobalt recovery method according to the second embodiment.

Fig. 18 is a flowchart showing steps of a method for recovering lithium contained in a liquid to be treated.

Fig. 19 is a schematic diagram showing a schematic configuration of a processing apparatus used in the cobalt recovery method of fig. 17.

Fig. 20 is a schematic diagram showing a schematic configuration of the bipolar membrane electrodialysis device.

Fig. 21 is a flowchart schematically showing steps of a variation of the cobalt recovery method according to the second embodiment.

Fig. 22 is a schematic diagram showing a schematic configuration of a processing apparatus used in the cobalt recovery method of fig. 21.

Fig. 23 is a flowchart schematically showing the steps of a cobalt recovery method according to a modification of the cobalt recovery method according to the second embodiment.

Fig. 24 is a schematic diagram showing a schematic configuration of a processing apparatus used in the cobalt recovery method of fig. 23.

Detailed Description

An embodiment of the cobalt recovery method of the present disclosure will be described below with reference to the drawings.

[ cobalt recovery method of the first embodiment ]

As a method for recovering cobalt from a spent lithium ion battery, patent document 1 describes a method for recovering cobalt by performing the following steps: an acid leaching step of leaching the waste lithium ion battery with sulfuric acid to dissolve cobalt; a low pH adjustment step of adjusting the pH of the solution to be treated containing cobalt dissolved therein to 4 to 5 by adding an alkali thereto to precipitate a salt of an impurity metal such as aluminum dissolved together with cobalt in the form of crystals; and a high pH adjustment step of adjusting the pH of the treatment liquid to 7 or more and 10 or less by further adding an alkali after removing the precipitate, thereby precipitating a cobalt salt in a crystal form. However, the method described in patent document 1 may leave impurity metals such as aluminum in the treatment target liquid after the low pH adjustment step, and if the impurity metals remain in the treatment target liquid, the impurity metals are mixed into cobalt as a target recovered product, and the purity of cobalt is lowered. The cobalt recovery method according to the first aspect is made to solve the above problem, and an object thereof is to provide a cobalt recovery method capable of recovering cobalt with high purity from a liquid to be treated in which at least cobalt and an impurity metal are dissolved.

Patent document 1: japanese patent No. 5077788

A cobalt recovery method according to a first aspect of the present disclosure is characterized by including the steps of: a primary low-pH adjustment step of adding an alkali to an acidic treatment target solution in which at least cobalt and impurity metals are dissolved to adjust the pH to 4 or more and 7 or less; a primary impurity metal separation step of separating a precipitate containing crystals of a salt of an impurity metal precipitated in the primary low pH adjustment step from a liquid to be treated by using a solid-liquid separator; a primary high pH adjustment step of adjusting the pH to 7 or more by adding an alkali to the liquid to be treated after the primary impurity metal separation step; a primary cobalt separation step of separating a precipitate containing crystals of a cobalt salt precipitated in the primary high pH adjustment step from a liquid to be treated by using a solid-liquid separator; a re-dissolving step of dissolving the precipitate separated in the primary cobalt separation step by adding an inorganic acid to generate a re-dissolved solution; a secondary low pH adjustment step of adding an alkali to the redissolution to adjust the pH to 4 to 7; a secondary impurity metal separation step of precipitating a precipitate containing crystals of the impurity metal salt precipitated in the secondary low pH adjustment step by its own weight or centrifugal separation, and separating the precipitate into a supernatant liquid and a slurry containing the precipitate; a secondary high pH adjustment step of adjusting the pH to 7 or more by adding an alkali to a redissolution as a supernatant after the secondary impurity metal separation step; and a secondary cobalt separation step of recovering a precipitate containing crystals of a cobalt salt precipitated in the secondary high pH adjustment step from the redissolved solution by using a solid-liquid separation apparatus.

The cobalt recovery process described in paragraph 0012 can be configured in the following manner: the slurry containing the precipitate separated in the secondary impurity metal separation step is supplied to at least one of the liquid to be treated before the primary low pH adjustment step, the liquid to be treated in the primary low pH adjustment step, and the liquid to be treated before the primary impurity metal separation step.

Further, the cobalt recovery method described in paragraph 0012 or paragraph 0013 may be configured in the following manner: further comprising a solvent extraction step of performing solvent extraction using an extraction agent on the redissolved solution produced in the redissolving step to separate impurity metals from the redissolved solution, wherein in the secondary low pH adjustment step, a base is added to the redissolved solution after the solvent extraction step to adjust the pH to 4 or more and 7 or less.

Further, the cobalt recovery method described in paragraph 0012 or paragraph 0013 may be configured in the following manner: further comprising a solvent extraction step of performing solvent extraction using an extractant on the redissolved solution as a supernatant after the secondary impurity metal separation step to separate impurity metals from the redissolved solution, wherein the secondary high pH adjustment step is performed by adding an alkali to the redissolved solution after the solvent extraction step to adjust the pH to 7 or more.

Further, the cobalt recovery method described in paragraph 0012 or paragraph 0013 may be configured in the following manner: further comprising the steps of: a re-dissolution step of adding an inorganic acid to dissolve the precipitate separated in the secondary cobalt separation step, thereby producing a re-dissolved solution; a solvent extraction step of extracting the redissolved solution with a solvent using an extractant to separate impurity metals from the redissolved solution; a third high pH adjustment step of adjusting the pH to 7 or more by adding an alkali to the redissolved solution after the solvent extraction step; and a third cobalt separation step of separating a precipitate containing a crystal of the cobalt salt precipitated in the third high pH adjustment step from the redissolved solution.

Additionally, the cobalt recovery process of any of paragraphs 0012 to 0015 can be configured in the following manner: the method further comprises an acid leaching step of leaching the waste lithium ion battery with inorganic acid to dissolve cobalt and impurity metals, thereby obtaining the treated liquid.

Additionally, the cobalt recovery process of any one of paragraphs 0012 to 0016 can be configured in the following manner: the method for recovering cobalt further comprises the steps of: a concentration step of evaporating and concentrating the treated liquid after the primary cobalt separation step; 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 lithium separation step of separating precipitates containing crystals of lithium carbonate precipitated in the carbonation step from the liquid to be treated.

In addition, the cobalt recovery method described in paragraph 0018 can be configured in the following manner: in the concentration step, the redissolved solution after the secondary cobalt separation step is evaporated and concentrated.

According to the cobalt recovery method of the first aspect of the present disclosure, the solution to be treated in which at least cobalt and impurity metals are dissolved is first adjusted to pH 4 or more and 7 or less by adding alkali in the first low pH adjustment step, thereby removing the impurity metals from the solution to be treated, and is adjusted to pH 7 or more by adding alkali in the first high pH adjustment step, thereby precipitating cobalt contained in the solution to be treated as a cobalt salt. Then, the precipitated cobalt salt is dissolved with an inorganic acid in the redissolution step, and a base is added to the redissolution in the secondary low pH adjustment step to adjust the pH to 4 or more and 7 or less, whereby even if the salt of the impurity metal remaining in the liquid to be treated is precipitated together with the precipitated cobalt salt in the primary high pH adjustment step and mixed into the redissolved liquid, the remaining impurity metal can be removed from the redissolved liquid. In the secondary high pH adjustment step, the pH of the redissolved solution from which the impurity metals have been removed is adjusted to 7 or more by adding an alkali, and cobalt is precipitated as a cobalt salt, whereby cobalt contained in the liquid to be treated can be recovered with high purity.

Fig. 1 and 2 show steps of respective steps in an embodiment of a cobalt recovery method according to a first embodiment of the present disclosure, and fig. 3 and 4 show a schematic configuration of a treatment apparatus for carrying out the cobalt recovery method according to the present embodiment. The cobalt recovery method according to the present embodiment can be suitably used for recovering cobalt from an acidic treatment target solution containing at least cobalt and an impurity metal, and can be particularly suitably used for recovering cobalt from a waste lithium ion battery. The following description will be given by taking, as an example, a case of recovering cobalt from a waste lithium ion battery and further recovering lithium.

The cobalt recovery method of the present embodiment includes the steps of:

-an acid leaching step S1 of leaching the spent lithium ion battery with a mineral acid to dissolve cobalt and impurity metals and further to dissolve at least lithium;

a solid-liquid separation step S2 of separating an insoluble residue from the acidic liquid to be treated in which at least cobalt, impurity metals, and lithium are dissolved, which is obtained in the acid leaching step S1;

a primary low pH adjustment step S3 of adding an alkali to the liquid to be treated from which the insoluble residue is removed after the solid-liquid separation step S2 to adjust the pH to 4 or more and 7 or less;

a solid-liquid separation step S4 of separating a precipitate containing crystals of the salt of the impurity metal precipitated in the primary low pH adjustment step S3 from the liquid to be treated (primary impurity metal separation step);

a primary high pH adjustment step S5 of adding an aqueous alkaline solution to the treated liquid from which the precipitate has been removed after the solid-liquid separation step S4 to adjust the pH to 7 or more;

a solid-liquid separation step S6 of separating a precipitate containing crystals of a cobalt salt precipitated in the primary high pH adjustment step S5 from the liquid to be treated (primary cobalt separation step);

a redissolution step S7-1 of adding an inorganic acid to dissolve the precipitate separated in the solid-liquid separation step S6 to produce a redissolution;

a secondary low pH adjustment step S7-2 of adding an alkali to the redissolved solution to adjust the pH to 4 or more and 7 or less;

a precipitation step S7-3 (secondary impurity metal separation step) of precipitating the precipitate containing the crystals of the impurity metal salt precipitated in the secondary low pH adjustment step S7-2 by its own weight or by centrifugal separation, and separating the precipitate into a supernatant and a slurry containing the precipitate;

a secondary high pH adjustment step S7-4 of adding an alkali to the redissolved solution as a supernatant after the precipitation step S7-3 to adjust the pH to 7 or more; and (c) a second step of,

a solid-liquid separation step S7-5 (secondary cobalt separation step) of recovering a precipitate containing crystals of a cobalt salt precipitated in the second high pH adjustment step S7-4 from the redissolved solution by using a solid-liquid separator.

The cobalt recovery method of the present embodiment further includes the following steps for further recovering lithium:

an impurity removal step S8-1 of chelating the treatment target liquid from which the precipitate has been removed and in which lithium and an inorganic salt have been dissolved after the solid-liquid separation step S6;

a concentration step S8-2 of evaporating and concentrating the treated liquid after the impurity removal step S8-1;

a crystallization step S8-3 of cooling and crystallizing the liquid to be treated after the concentration step S8-2 to precipitate an inorganic salt in a crystal form;

a solid-liquid separation step S8-4 for separating a precipitate containing crystals of the inorganic salt precipitated in the crystallization step S8-3 from the liquid to be treated;

a carbonation step S8-5 of mixing carbon dioxide and/or adding a water-soluble carbonate to the treated liquid from which the precipitate has been removed after the solid-liquid separation step S8-4;

a solid-liquid separation step S8-6 (lithium separation step) for separating a precipitate containing crystals of lithium carbonate precipitated in the carbonation step S8-5 from the liquid to be treated;

a dissolving step S8-7 of dissolving the precipitate containing the crystals of the inorganic salt separated in the solid-liquid separation step S8-4 by adding an inorganic acid; and the number of the first and second groups,

and an electrodialysis step S8-8 of subjecting the inorganic salt solution obtained in the dissolution step S8-7, in which the inorganic salt is dissolved, to bipolar membrane electrodialysis to separate the alkali and the inorganic acid from the inorganic salt solution.

The used lithium ion batteries, which are objects of cobalt recovery, include used lithium ion batteries in which the charge capacity is reduced by using a predetermined number of charges and discharges, semi-finished products generated by defects in the battery manufacturing process, and prototype number stock products generated by product specification changes. The spent lithium ion battery may be subjected to a baking treatment, or may be simply pulverized, or may be a powder obtained by pulverizing and baking.

First, in the acid leaching step S1, the spent lithium ion battery is leached with an inorganic acid. Thereby dissolving valuable metals such as cobalt and lithium contained in the waste lithium ion battery. In this acid leaching, in addition to the valuable metal, the impurity metal is also dissolved. The impurity metal is not particularly limited, and examples thereof include copper, aluminum, and iron, and at least 1 of copper, aluminum, and iron is dissolved. Examples of the inorganic acid include sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid, and in this embodiment, sulfuric acid is used from the viewpoint of low cost and easy handling.

In the acid leaching step S1, the method for leaching the spent lithium ion battery with the inorganic acid is not particularly limited, and a commonly used method can be used. For example, in the acid leaching tank 1, 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, thereby producing a treatment solution in which the cobalt, lithium, and impurity metals are dissolved. In the acid leaching step S1, the concentration of the inorganic acid in the aqueous solution is preferably 1mol/L to 5mol/L, and the temperature of the aqueous solution is preferably 60 ℃ or higher.

The liquid to be treated obtained in the acid leaching step S1 is supplied to a solid-liquid separation step S2. In the solid-liquid separation step S2, an insoluble residue is separated from the liquid to be treated by using the solid-liquid separator 2. The insoluble residue is a carbon material, a metal material, or an organic material, which is mainly insoluble in an inorganic acid and is contained in the spent lithium ion battery. As a method for performing solid-liquid separation, for example, various filtering devices such as pressure filtration (filter press), vacuum filtration, and centrifugal filtration, and a known solid-liquid separation device such as a centrifugal separation device of a decantation type can be used. The same applies to the solid-liquid separation steps S4, S6, S7-5, S8-4, S8-6, and the like described below.

The liquid to be treated after the solid-liquid separation step S2 is supplied to the primary low pH adjustment step S3. In the primary low pH adjustment step S3, an alkali is added to the liquid to be treated to adjust the pH of the liquid to be treated to 4 or more and 7 or less, preferably 4 or more and 6 or less, more preferably 4 or more and 5 or less. As a result, the impurity metals (e.g., copper, aluminum, and iron) in the treatment liquid are precipitated in the form of crystals of inorganic salts such as hydroxides, and removed from the treatment liquid. As the base used for pH adjustment, for example, sodium hydroxide, potassium hydroxide, lithium hydroxide, or the like can be used, and in the present embodiment, sodium hydroxide is used from the viewpoint of low cost and easy handling.

In the primary low 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. Examples thereof include: a method of adding an aqueous alkali solution such as an aqueous sodium hydroxide solution to the treatment solution while stirring the treatment solution in the primary low pH adjustment tank 3. The low pH adjustment step S3 is preferably performed once while raising the temperature of the liquid to be treated to a constant temperature, for example, in the range of 30 ℃ to 80 ℃.

The aqueous alkali solution added in the first low pH adjustment step S3 is preferably diluted to an alkali concentration of less than 1.0mol/L. This can prevent cobalt in the treatment liquid from precipitating as crystals of a cobalt salt together with the impurity metal in the primary low pH adjustment step S3 and can remove cobalt from the treatment liquid. However, if the alkali concentration is too low, it is necessary to adjust the pH by using a large amount of an alkali aqueous solution in the first low pH adjustment step S3, and the amount of the liquid to be treated after pH adjustment is also large, so the lower limit of the alkali concentration is preferably 0.1mol/L or more. In addition, in order to effectively suppress the removal of cobalt in the treatment target liquid from the treatment target liquid in the primary low pH adjustment step S3, the alkali concentration of the aqueous alkali solution added in the primary low pH adjustment step S3 is preferably 0.5mol/L or less, and more preferably 0.2mol/L or less.

In the primary low pH adjustment step S3, in order to reduce the amount of the aqueous alkali solution used for pH adjustment, the pH of the liquid to be treated may be adjusted to 4 or more and 7 or less by adding an aqueous alkali solution having a high 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 of less than 4 and, after the pH of the liquid to be treated reaches the predetermined value, adding an aqueous alkali solution having a dilute alkali concentration of less than 1.0mol/L to the liquid to be treated. The predetermined value of the pH of the liquid to be treated may be set in a range of 2 to 3.

The liquid to be treated after the primary low pH adjustment step S3 is supplied to the solid-liquid separation step S4. In the solid-liquid separation step S4, a precipitate containing crystals of the salt of the impurity metal precipitated in the primary low pH adjustment step S3 is separated from the liquid to be treated by using the solid-liquid separator 4. The precipitate recovered in the solid-liquid separation step S4 is washed with a washing liquid. The washing waste liquid after washing is preferably supplied to the subsequent primary high pH adjustment step S5 together with the liquid to be treated. Thus, cobalt contained in the washing waste liquid can be recovered, lithium can be supplied from the primary high pH adjustment step S5 to the carbonation step S8-5 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 S8-5. The water used for washing the precipitates is not particularly limited, and condensed water generated when the liquid to be treated is concentrated by evaporation in the concentration step S8-2 is preferably used, whereby the condensed water can be effectively used.

The liquid to be treated after the solid-liquid separation step S4 is supplied to the primary high pH adjustment step S5. In the primary high pH adjustment step S5, a base is added to the liquid to be treated to adjust the pH to 7 or more, preferably 7 or more and 13 or less, more preferably 7 or more and 11 or less, and still more preferably 8 or more and 10 or less. Thus, cobalt in the treatment liquid precipitates in the form of a crystal of a cobalt salt such as cobalt hydroxide. In the primary high pH adjustment step S5, in addition to cobalt, valuable metals such as nickel and manganese, and impurity metals remaining in the treatment target liquid are precipitated in the form of crystals of inorganic salts such as hydroxides, and can be removed from the treatment target liquid. As the base used for pH adjustment, for example, sodium hydroxide, potassium hydroxide, lithium hydroxide, or the like can be used, and in the present embodiment, sodium hydroxide is used from the viewpoint of low cost and easy handling.

The method for adjusting the pH of the liquid to be treated in the primary high pH adjustment step S5 is not particularly limited, and a commonly-used method can be used. Examples thereof include: a method of adding an aqueous alkali solution such as an aqueous sodium hydroxide solution to the liquid to be treated while stirring the liquid in the primary high pH adjustment tank 5. When the pH is adjusted, the temperature of the liquid to be treated is preferably raised to a constant temperature in the range of, for example, 30 ℃ to 80 ℃. The alkali concentration of the aqueous alkali solution added in the primary high pH adjustment step S5 is not particularly limited, but is preferably not less than the alkali concentration of the aqueous alkali solution used in the primary low pH adjustment step S4, and more preferably not less than 0.2 mol/L.

The liquid to be treated after the primary high pH adjustment step S5 is supplied to the solid-liquid separation step S6. In the solid-liquid separation step S6, a precipitate containing crystals of the cobalt salt precipitated in the primary high pH adjustment step S5 is separated from the treatment target liquid by using the solid-liquid separator 6. The precipitate recovered in the solid-liquid separation step S6 is washed with a washing liquid. The washing waste liquid after washing is preferably supplied to the impurity removal step S8-1 together with the liquid to be treated. Thus, lithium contained in the washing waste liquid can be supplied from the impurity removal step S8-1 to the carbonation step S8-5 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 S8-5. The water used for washing the precipitate is not particularly limited, and condensed water generated in the concentration step S8-2 is preferably used, whereby the condensed water can be effectively used.

The precipitate recovered in the solid-liquid separation step S6 contains impurity metals in addition to cobalt. Therefore, the precipitate recovered in the solid-liquid separation step S6 is supplied to the re-dissolution step S7-1 in order to remove the remaining impurity metals.

In the redissolution step S7-1, the precipitate including the crystal of the cobalt salt and the crystal of the salt of the impurity metal is dissolved by adding the inorganic acid. 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. The method for dissolving the precipitate is not particularly limited, and for example, a redissolution in which cobalt and an impurity metal are dissolved is produced by dissolving the precipitate in the redissolution tank 7 using an aqueous solution of an inorganic acid such as an aqueous sulfuric acid solution so as to have a desired concentration. In the redissolution step S7-1, the concentration of the inorganic acid in the aqueous solution is preferably 1mol/L to 5mol/L, and the temperature of the aqueous solution is preferably 30 ℃ or higher.

The redissolved solution obtained in the redissolution step S7-1 is supplied to the secondary low pH adjustment step S7-2. In the secondary low pH adjustment step S7-2, as in the primary low pH adjustment step S3, an alkali is added to the redissolved solution to adjust the pH of the redissolved solution to 4 or more and 7 or less, preferably 4 or more and 6 or less, and more preferably 4 or more and 5 or less. Thus, the impurity metal remaining in the redissolved solution is precipitated in the form of crystals of an inorganic salt such as a hydroxide, and the impurity metal remaining in the redissolved solution can be removed from the redissolved solution. As the base used for pH adjustment, for example, sodium hydroxide, potassium hydroxide, lithium hydroxide, or the like can be used, and in the present embodiment, sodium hydroxide is used from the viewpoint of low cost and easy handling.

The method for adjusting the pH of the redissolution in the secondary low pH adjustment step S7-1 is not particularly limited, and a commonly used method can be used. Examples thereof include: a method of adding an aqueous alkali solution such as an aqueous sodium hydroxide solution while stirring the redissolved solution in the secondary low pH adjustment tank 8. The second low pH adjustment step S7-2 is preferably performed while raising the temperature of the redissolved solution to a constant temperature, for example, in the range of 30 ℃ to 80 ℃.

The aqueous alkali solution added in the secondary low pH adjustment step S7-2 is preferably diluted to an alkali concentration of less than 1.0mol/L. This can prevent cobalt in the redissolved solution from precipitating as crystals of a cobalt salt together with the impurity metal in the secondary low pH adjustment step S7-2 and removing the cobalt from the redissolved solution. However, if the alkali concentration is too low, it is necessary to adjust the pH by using a large amount of an alkali aqueous solution in the secondary low pH adjustment step S7-2, and the amount of the redissolved solution after the pH adjustment increases, so the lower limit of the alkali concentration is preferably 0.1mol/L or more. In addition, in order to effectively suppress the removal of cobalt in the redissolved solution from the redissolved solution in the secondary low pH adjustment step S7-2, the alkali concentration of the aqueous alkali solution added in the secondary low pH adjustment step S7-2 is preferably 0.5mol/L or less, and more preferably 0.2mol/L or less.

In the secondary low pH adjustment step S7-2, in order to reduce the amount of the aqueous alkali solution used for pH adjustment, an aqueous alkali solution having a high alkali concentration of 1.0mol/L or more may be added to the redissolution until the pH of the redissolution reaches a predetermined value of less than 4, and after the pH of the redissolution reaches the predetermined value, an aqueous alkali solution having a dilute alkali concentration of less than 1.0mol/L may be added to the redissolution, thereby adjusting the pH of the redissolution to 4 or more and 7 or less. The predetermined value of the pH of the redissolution may be set in a range of 2 to 3.

The redissolved solution after the secondary low pH adjustment step S7-2 is supplied to the precipitation step S7-3. The precipitation step S7-3 is not particularly limited, and for example, the precipitate of the crystals of the salt containing the impurity metal precipitated in the secondary low pH adjustment step S7-2 is naturally precipitated by its own weight in the precipitation tank 9, and is thereby precipitated and separated into a supernatant liquid and a slurry containing the precipitate. The slurry containing precipitates obtained by collecting the supernatant liquid is preferably supplied to at least one of the liquid to be treated before the primary low pH adjustment step S3, the liquid to be treated in the primary low pH adjustment step S3, and the liquid to be treated supplied to the solid-liquid separation step S4. Since the slurry obtained in the precipitation step S7-3 contains cobalt, when the slurry is directly recovered as an impurity, a loss of cobalt is generated in the recovery. By supplying the slurry to at least one of the liquid to be treated before the first low pH adjustment step S3, the liquid to be treated in the first low pH adjustment step S3, and the liquid to be treated in the solid-liquid separation step S4, cobalt contained in the slurry can be supplied to the first high pH adjustment step S5, whereby cobalt can be precipitated again as crystals in the form of a cobalt salt in the first high pH adjustment step S5, and the cobalt can be returned to the step of recovering cobalt after the redissolution step S7-1 in the form of a cobalt salt, whereby cobalt can be recovered at a high recovery rate.

In the precipitation step S7-3, the precipitate containing the crystals of the salt of the impurity metal precipitated in the secondary low pH adjustment step S7-2 may be precipitated by centrifugal separation by settling the precipitate by centrifugal force, and separated into a supernatant liquid and a slurry containing the precipitate. For the centrifugal separation, a known centrifugal separator can be used.

The re-dissolved solution obtained by removing the impurity metals from the supernatant solution obtained by the precipitation step S7-3 in which cobalt is dissolved is supplied to the secondary high pH adjustment step S7-4. In the secondary high pH adjustment step S7-4, as in the primary high pH adjustment step S5, a base is added to the redissolution to adjust the pH to a range of 7 or more, preferably 7 or more and 13 or less, more preferably 7 or more and 11 or less, and still more preferably 8 or more and 10 or less. As a result, cobalt in the redissolution is precipitated as a crystal of a cobalt salt such as cobalt hydroxide. In the second high pH adjustment step S7-4, in addition to cobalt, valuable metals such as nickel and manganese are precipitated in the form of crystals of inorganic salts such as hydroxides, and can be removed from the redissolved solution. As the base used for pH adjustment, for example, sodium hydroxide, potassium hydroxide, lithium hydroxide, or the like can be used, and in the present embodiment, sodium hydroxide is used from the viewpoint of low cost and easy handling.

The method for adjusting the pH of the redissolution in the second high pH adjustment step S7-4 is not particularly limited, and a method generally used may be used. Examples thereof include: a method of adding an aqueous alkali solution such as an aqueous sodium hydroxide solution while stirring the redissolved solution in the secondary high pH adjustment tank 10. In the pH adjustment, the temperature of the redissolved solution is preferably raised to a constant temperature, for example, in the range of 30 ℃ to 80 ℃. The alkali concentration of the aqueous alkali solution added in the secondary high pH adjustment step S7-4 is not particularly limited, but is preferably not less than the alkali concentration of the aqueous alkali solution used in the secondary low pH adjustment step S7-2, and more preferably not less than 0.2 mol/L.

The redissolved solution after the secondary high pH adjustment step S7-4 is supplied to a solid-liquid separation step S7-5. In the solid-liquid separation step S7-5, a precipitate containing crystals of the cobalt salt precipitated in the secondary high pH adjustment step S7-4 is separated from the redissolved solution by using a solid-liquid separator 11. Thus, cobalt dissolved in the treatment liquid can be precipitated as a cobalt salt and recovered.

The precipitate recovered in the solid-liquid separation step S7-5 is washed with a washing liquid. The washed waste washing liquid is preferably supplied to the impurity removal step S8-1 together with the redissolved solution. Thus, lithium contained in the redissolution solution or the waste washing liquid can be supplied from the impurity removal step S8-1 to the carbonation step S8-5, and lithium can be recovered at a high recovery rate by carbonation in the carbonation step S8-5. The water used for washing the precipitate is not particularly limited, and condensed water generated in the concentration step S8-2 is preferably used, whereby the condensed water can be effectively used. In the present embodiment, the washing waste liquid after washing is supplied to the impurity removal step S8-1 together with the redissolved solution, and thus, when calcium and/or magnesium are contained in the washing waste liquid or the redissolved solution, they are removed in the impurity removal step S8-1, but when the washing waste liquid or the redissolved solution does not contain calcium and/or magnesium, the liquid can be supplied to the concentration step S8-2. The washing waste liquid and the redissolution liquid may be supplied to the primary low pH adjustment step S3. Thus, the recovery rate of cobalt can be improved when cobalt is not precipitated in the secondary high pH adjustment step S7-4 and remains in the redissolution.

Next, in addition to lithium, an inorganic salt (sodium sulfate in the present embodiment) is dissolved in the liquid to be treated after the solid-liquid separation step S6 by the inorganic acid (sulfuric acid in the present embodiment) and the alkali (sodium hydroxide in the present embodiment) added in the acid leaching step S1, the primary low pH adjustment step S3, the primary high pH adjustment step 5, and the like. In addition, impurities such as calcium, magnesium, and silicon are generally dissolved in the liquid to be treated. A method for recovering lithium in a liquid to be treated will be described below with reference to fig. 2 and 4.

The liquid to be treated after the solid-liquid separation step S6 is supplied to the impurity removal step S8-1. In the impurity removal step S8-1, at least polyvalent cations such as calcium and/or magnesium contained in the liquid to be treated are removed. By removing calcium, magnesium, and the like contained as impurities in the liquid to be treated, scale can be prevented from being generated and attached to the heat transfer surface of the heat exchanger of the evaporation and concentration device 13 in the subsequent concentration step S8-2, and the heat exchange efficiency can be maintained high. When the treatment target liquid contains calcium, magnesium, or the like, polyvalent cations such as calcium, magnesium, or the like contained in the inorganic solution may precipitate in the cation exchange membrane of the bipolar membrane electrodialysis device 19 in the electrodialysis step S8-8, thereby deteriorating the membrane performance. Therefore, by removing in advance substances such as calcium and magnesium that cause problems such as scaling during the electrodialysis operation from the liquid to be treated, it is possible to prevent adverse effects on the cation exchange membrane of the bipolar membrane electrodialysis device 19 and maintain the performance of electrodialysis high.

The method for removing calcium and magnesium from the liquid to be treated in the impurity removal step S8-1 is not particularly limited, and, for example, a polyvalent cation removal device 12 can be used. The polyvalent cation removal device 12 is a device for removing polyvalent cations having valence 2 or more, such as calcium ions and magnesium ions, and for example, a device having an ion exchange resin therein and capable of adsorbing calcium ions and magnesium ions when a liquid to be treated contacts the ion exchange resin can be exemplified. As the polyvalent cation removal apparatus 12, an apparatus having a configuration capable of introducing the liquid to be treated into a column filled with a chelate resin may be exemplified. As the chelate resin, a 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 12 may be a device to which a chelating agent is added. In the impurity removal step S8-1, the impurities removed from the treatment target liquid include silicon (silicate ions) in addition to calcium and magnesium.

The liquid to be treated after the impurity removal step S8-1 is supplied to the concentration step S8-2. In the concentration step S8-2, the liquid to be treated is heated to evaporate and concentrate, i.e., the water in the liquid to be treated is evaporated to thereby concentrate 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 S8-5 described later.

In the concentration step S8-2, the liquid to be treated is preferably evaporated and concentrated to such a concentration that lithium is not precipitated in the concentrated liquid to be treated in a crystal form of a lithium salt such as lithium sulfate, for example. 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 S8-5.

When the precipitate is precipitated in the concentration step S8-2, a solid-liquid separation step of separating the precipitate from the liquid to be treated may be performed.

In the concentration step S8-2, the method for evaporating and concentrating the liquid to be treated is not particularly limited, and, for example, the evaporation and concentration apparatus 13 can be used. The evaporation concentration device 13 is not particularly limited as long as it can concentrate the liquid to be treated by evaporation, and a known evaporation concentration device such as a heat pump type, an ejector (injector) type, a steam type, or a flash 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 13 is connected to a vacuum pump, not shown, to maintain the inside at a low pressure, and in the concentration step S8-2, it is preferable to perform evaporation and concentration by heating the liquid to be treated at a low pressure lower than atmospheric pressure. Since 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, the energy required for evaporation and concentration of the liquid to be treated can be suppressed to be low by performing evaporation and concentration at low pressure, and energy saving can be achieved.

In the concentration step S8-2, the evaporation concentration is not necessarily performed by heating the treatment target liquid at a low pressure lower than the atmospheric pressure, and for example, the evaporation concentration may be performed by heating the treatment target liquid at the atmospheric pressure.

The liquid to be treated after the concentration step S8-2 is supplied to the crystallization step S8-3. In the crystallization step S8-3, the liquid to be treated is cooled and crystallized. In the crystallization step S8-3, the temperature of the liquid to be treated is lowered to lower the solubility until the inorganic salt contained in the liquid to be treated is crystallized, whereby the concentration of the inorganic salt (sodium sulfate in the present embodiment) in the liquid to be treated can be lowered. Therefore, when lithium carbonate is recovered in the carbonation step S8-5, the purity of lithium carbonate can be increased.

In the crystallization step S8-3, the method for cooling and crystallizing the liquid to be treated is not particularly limited, and, for example, the cooling and crystallizing device 14 can be used. The cooling crystallization apparatus 14 is an apparatus for cooling the supplied liquid to be treated in the crystallization tank to precipitate crystals of the target inorganic salt. As the cooling crystallization apparatus 14, 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 S8-3, only crystals of the target inorganic salt are precipitated by utilizing the fact that the saturated solubility and the temperature dependency 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 crystals of sodium sulfate is 30 ℃ or lower, and preferably 5 ℃ to 20 ℃ inclusive. At this time, sulfuric acidSodium as sodium sulfate decahydrate (Na) ₂ SO ₄ ·10H ₂ O) is precipitated.

The liquid to be treated after the crystallization step S8-3 is supplied to the solid-liquid separation step S8-4. In the solid-liquid separation step S8-4, a precipitate containing crystals of an inorganic salt (sodium sulfate in the present embodiment) is separated from the liquid to be treated by using the solid-liquid separator 15.

The liquid to be treated after the solid-liquid separation step S8-4 is supplied to the carbonation step S8-5. In the carbonation step S8-5, 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 removed, thereby precipitating lithium in the treatment target liquid in the form of 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 S8-5, carbon dioxide is preferably mixed into the liquid to be treated to precipitate crystals of lithium carbonate. In this way, by using a material containing no alkali metal such as sodium in the carbonation step S8-5, it is possible to suppress the alkali metal other than lithium from being mixed into the crystals of the precipitated lithium carbonate. 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 S8-5, the method of mixing carbon dioxide with 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 16, 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 S8-5. This reduces the solubility of lithium carbonate generated by the reaction between lithium and carbon dioxide in the treatment target liquid, thereby increasing 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 precipitation of crystals of the inorganic salt together with crystals of lithium carbonate, and therefore, when lithium carbonate is recovered in the carbonation step S8-5, the purity of lithium carbonate can be increased.

The method for raising the temperature of the treatment target liquid in the carbonation step S8-5 is not particularly limited, and a method for heating the treatment target liquid in the carbonation tank 16 using a known heating device such as a heater may be used. The following embodiments may be applied: before the liquid to be treated is supplied to the carbonating tank 16, the temperature of the liquid to be treated is raised in advance by using a preheating means such as a heat exchanger.

The liquid to be treated after the carbonation step S8-5 is supplied to the solid-liquid separation step S8-6. In the solid-liquid separation step S8-6, a precipitate containing crystals of lithium carbonate is separated from the liquid to be treated by the solid-liquid separator 17. The precipitate recovered from the liquid to be treated is washed with water or the like to remove impurities, whereby the purity of lithium carbonate can be improved. The water used for washing the precipitate is not particularly limited, but condensed water in the concentration step S8-2 is preferably used, whereby the condensed water can be effectively used.

The liquid to be treated after the solid-liquid separation step S8-6 is not particularly limited, but it preferably contains impurities, and a part of the liquid is discharged as a discharge 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 also preferable that the washing waste liquid after washing the precipitate containing the crystals of lithium carbonate is recirculated in the system together with the liquid to be treated after the solid-liquid separation step S8-6.

When the liquid to be treated after the solid-liquid separation step S8-6 is circulated again in the system, it is preferably supplied to the concentration step S8-2 (the evaporation and concentration apparatus 13) to be evaporated and concentrated, and preferably supplied to the primary low pH adjustment step S3 (the primary low pH adjustment tank 3) and/or the primary high pH adjustment step S5 (the primary high pH adjustment tank 5). Since the liquid to be treated after the solid-liquid separation step S8-6 is alkaline, it can be used as the alkali to be added in the first low pH adjustment step S3 and the first high pH adjustment step S5. Further, when the liquid to be treated after the solid-liquid separation step S8-6 contains a large amount of carbonate ions (CO) ₃ ^2- ) In the concentration step S8-2, crystals of carbonate are precipitated on the heat transfer surface of the heat exchanger of the evaporation and concentration apparatus 13. Here, the liquid to be treated supplied to the first low pH adjustment step S3 and the first high pH adjustment step S5 is acidic, and the liquid to be treated after the solid-liquid separation step S8-6 is neutralized with the acidic liquid to be treated, so that carbonate ions are released as carbon dioxide, and thus precipitation of crystals of carbonate on the heat transfer surface of the heat exchanger of the evaporation and concentration apparatus 13 in the concentration step S8-2 can be prevented.

On the other hand, crystals of the inorganic salt (sodium sulfate in the present embodiment) contained in the precipitate precipitated in the concentration step S8-2 and recovered in the solid-liquid separation step S8-4 are supplied to the dissolution step S8-7. The dissolving step S8-7 is not particularly limited, and for example, an inorganic salt solution is produced by dissolving crystals of an inorganic salt with, for example, water so as to form a desired concentration in the dissolving tank 18. 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, and condensed water generated in the concentration step S8-2 is preferably used, whereby the condensed water can be effectively used.

The inorganic salt solution obtained in the dissolving step S8-7 is supplied to the electrodialysis step S8-8. The electrodialysis step S8 to 8 is not particularly limited, and for example, the base and the inorganic acid are separated and recovered from the inorganic salt solution by the bipolar membrane electrodialysis device 19. As the bipolar membrane electrodialysis device 19, for example, a bipolar membrane electrodialysis device of a three-compartment cell system shown in fig. 5, in which a plurality of cells 190 are laminated, is suitably used, and the cells 190 are provided with an anion exchange membrane 191, a

cation exchange membrane

192, and 2

bipolar membranes

193 and 194 between an anode 195 and a cathode 196. In the bipolar membrane electrodialysis device 19 of the present embodiment, a desalination chamber R1 is formed by the anion exchange membrane 191 and the cation exchange membrane 192, an acid chamber R2 is formed between the anion exchange membrane 191 and one piece of the bipolar membrane 193, and an alkali chamber R3 is formed between the cation exchange membrane 192 and the other piece of the bipolar membrane 194. An anode chamber R4 and a cathode chamber R5 are formed outside each

bipolar membrane

193 and 194, an anode 195 is disposed in the anode chamber R4, and a cathode 196 is disposed in the cathode chamber R5.

In the electrodialysis step S8-8, 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 sulfate, sodium ions (Na) are present in the desalting chamber R1 ⁺ ) Passing through cation exchange membrane 192, sulfate ion (SO) ₄ ^2- ) Through an anion exchange membrane 191. 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 193 and 194 ⁺ ) And hydroxide ion (OH) ^- ) Hydrogen ion (H) in acid chamber R2 ⁺ ) With sulfate ions (SO) ₄ ^2- ) Combine to form sulfuric acid (H) ₂ SO ₄ ) In the alkaline chamber R3, hydroxide ion (OH) ^- ) With sodium ion (Na) ⁺ ) Binding to form sodium hydroxide (NaOH). Thus, sulfuric acid (H) as an inorganic acid is recovered from the acid chamber R2 ₂ SO ₄ ) Sodium hydroxide (NaOH) is recovered as a base from the base chamber R3. The pure water introduced into the acid chamber R2 and the alkali chamber R3 can utilize condensed water generated in the concentration step S8-2.

The desalted dilute inorganic salt solution (desalted solution) 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 S8-2 (evaporation and concentration device 13) because a small amount of lithium is contained, and to carbonate the dilute inorganic salt solution in the carbonation step S8-5 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 S8-2 in the present embodiment, the desalted liquid may be supplied to the impurity removal step S8-1 when calcium and/or magnesium remain in the desalted liquid. Thus, calcium and magnesium can be removed from the desalted liquid and then supplied to the concentration step S8-2. The desalting solution may be supplied to the primary low 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 step S1 (acid leaching tank 1) and/or the redissolution step S7-1 (redissolution tank 7) and reused as the inorganic acid for acid leaching of the spent lithium ion battery and redissolution of a cobalt salt or the like. Further, it is preferably supplied to the impurity treatment step S8-1 (polyvalent cation removal device 12) and reused as a regenerated liquid of a chelate resin or an ion exchange resin.

The alkali (sodium hydroxide in the present embodiment) recovered from the alkali chamber R3 is not particularly limited, but is preferably supplied to the primary low pH adjustment step S3 (primary low pH adjustment tank 2) and/or the primary high pH adjustment step S5 (primary high pH adjustment tank 5) and/or the secondary low pH adjustment step S7-2 (secondary low pH adjustment tank 8) and/or the secondary high pH adjustment step S7-4 (secondary high pH adjustment tank 10) and reused as the alkali for adjusting the pH of the liquid to be treated and the redissolved solution. Further, it is preferably supplied to the impurity treatment step S8-1 (polyvalent cation removal device 12) and reused as a regenerated liquid of a chelate resin or an ion exchange resin.

In the cobalt recovery method according to the present embodiment, first, the solution to be treated in which at least cobalt and impurity metals are dissolved is subjected to the primary low pH adjustment step S3 in which alkali is added to adjust the pH to 4 or more and 7 or less, thereby removing the impurity metals from the solution to be treated, and is subjected to the primary high pH adjustment step S5 in which alkali is added to adjust the pH to 7 or more, thereby precipitating cobalt contained in the solution to be treated as a cobalt salt. Next, the precipitated cobalt salt is dissolved with an inorganic acid in the redissolution step S7-1, and the pH of the redissolution is adjusted to 4 or more and 7 or less by adding an alkali in the secondary low pH adjustment step S7-2, whereby the residual impurity metals can be removed from the redissolution even if the salts of the impurity metals remaining in the treatment target solution are precipitated together and mixed into the cobalt salt precipitated in the primary high pH adjustment step S5. Then, in a secondary high pH adjustment step S7-4, an alkali is added to the redissolved solution from which the impurity metals have been removed to adjust the pH to 7 or more; cobalt contained in the liquid to be treated can be recovered with high purity by precipitating as a cobalt salt.

Further, according to the cobalt recovery method of the present embodiment, the precipitate containing the crystals of the salt of the impurity metal precipitated in the secondary low pH adjustment step S7-2 is precipitated by its own weight in the precipitation step S7-3, thereby being separated into a supernatant liquid and a slurry containing the precipitate, and the redissolved solution as the supernatant liquid is recovered and supplied to the secondary high pH adjustment step S7-4. Thus, it is not necessary to provide a solid-liquid separation device as in the other solid-liquid separation step, and since the precipitate is precipitated by gravity and separated as a slurry, energy required for separation, washing of a filter, and the like are not necessary. Therefore, the cost can be reduced. In the case where the supernatant liquid and the slurry containing the precipitate are separated by the centrifugation in the precipitation step S7-3, the energy required for the separation is slightly increased, but the filter washing is not required, and the time required for the precipitation can be shortened.

The slurry obtained in the precipitation step S7-3 contains cobalt, and if this cobalt is not recovered, the recovery rate of cobalt decreases. Therefore, in the cobalt recovery method according to the present embodiment, the slurry obtained in the precipitation step S7-3 is supplied to at least one of the liquid to be treated before the primary low pH adjustment step S3, the liquid to be treated in the primary low pH adjustment step S3, and the liquid to be treated supplied to the solid-liquid separation step S4. In this way, since the precipitate contained in the slurry can be separated in the solid-liquid separation step S4, it is not necessary to separately provide a solid-liquid separation device for separating the precipitate from the slurry. Further, since the cobalt contained in the slurry can be precipitated again in the form of a cobalt salt in the primary high pH adjustment step S5 and the precipitated cobalt salt can be returned to the step of recovering cobalt after the redissolution step S7-1, the recovery rate of cobalt can be maintained high.

As described above, the cobalt recovery method according to the present embodiment can recover cobalt from a liquid to be treated with high purity at low cost.

In addition, according to the cobalt recovery method of the present embodiment, when removing the impurity metals from the treatment target solution and the redissolved solution in which cobalt and the impurity metals are dissolved in the first low pH adjustment step S3 and the second low pH adjustment step S7-2, the pH of the treatment target solution and the redissolved solution is adjusted with a dilute alkali aqueous solution having an alkali concentration of less than 1.0mol/L, whereby the removal of cobalt and the impurity metals from the treatment target solution and the redissolved solution can be suppressed. Therefore, the amounts of cobalt in the liquid to be treated and the redissolution supplied to the first high pH adjustment step 5 and the second high pH adjustment step S7-4 can be kept high, and thus cobalt can be recovered at a high recovery rate in the first high pH adjustment step 5 and the second high pH adjustment step S7-4.

Furthermore, 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 first low pH adjustment step S3 and the second low pH adjustment step S7-2, the amounts of the liquid to be treated and the redissolved solution increase in the carbonation step S8-5 for lithium recovery after the supply, but the amounts of the liquid to be treated and the redissolved solution decrease by evaporation and concentration of the liquid to be treated and the redissolved solution in the concentration step S8-2 before the carbonation step S8-5, and the lithium concentration in the liquid to be treated and the redissolved solution increases. Therefore, the recovery rate of lithium carbonate can be improved favorably in the carbonation step S8-5.

The present inventors performed the following tests on the alkali concentration of the aqueous alkali solution added in the first low pH adjustment step S3 and the second low pH adjustment step S7-2. Specifically, 200ml of an aqueous alkaline solution was added to an acidic solution having the components shown in table 1 below, thereby adjusting the pH of the acidic solution. As the aqueous alkali solution to be added, an aqueous lithium hydroxide solution was 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 acidic solution 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 acidic solution was increased gradually to 582mg in example 1, 585mg in example 2, and 599mg in example 3.

[ Table 1]

The pH-adjusted acidic solution was then filtered through a filter paper, and the content of each component 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 filtering the pH-adjusted acidic solution was confirmed. The results are shown in fig. 6 to 8. It should be noted that fig. 6 shows embodiment 1, fig. 7 shows embodiment 2, and fig. 8 shows embodiment 3. In fig. 8, it was visually confirmed that cobalt hydroxide was contained in the filtration residue of example 3, and in fig. 6 and 7, it was visually confirmed that cobalt hydroxide was not contained in the filtration residues of examples 1 and 2.

Based on the above results, it can be confirmed from fig. 6 to 8 that: when the alkali concentration of the aqueous alkali solution added to the acidic solution is 1.0mol/L, the filtration residue of the acidic solution after H adjustment contains a large amount of cobalt salt. Further, as can be seen from table 2, when the alkali concentration of the aqueous alkali solution added to the acidic solution was 1.0mol/L, the cobalt recovery rate of the acidic solution after pH adjustment was less than 85%, and when the alkali concentration was less than 1.0mol/L, the cobalt recovery rate of the acidic solution after pH adjustment was 85% or more, and a large amount of cobalt remained in the acidic solution.

As described above, in the first low pH adjustment step S3 and the second low pH adjustment step S7-2, the alkali concentration of the aqueous alkali solution added to the treatment target liquid and the redissolved solution is set to less than 1.0mol/L, whereby the removal of cobalt together with impurity metals from the treatment target liquid and the redissolved solution can be suppressed in the first low pH adjustment step S3 and the second low pH adjustment step S7-2, and the cobalt content in the treatment target liquid and the redissolved solution supplied to the first high pH adjustment step S5 and the second high pH adjustment step S7-4 can be maintained high.

For example, the throughput of the waste lithium ion battery during 1 year is 1000t, the content of cobalt in the waste lithium ion battery is 20%, when the recovery rate of cobalt is increased by 1%, a difference of 2t is generated in 1 year based on the recovery rate of cobalt, and when the unit price of cobalt is 6000 yen/kg, a difference of 12000000 yen is generated in 1 year.

In addition, according to the cobalt recovery method of the present embodiment, in the dissolving step S8-7, crystals of an inorganic salt (sodium sulfate in the present embodiment) contained in the precipitate separated from the treatment liquid in the solid-liquid separation step S8-4 are dissolved to prepare an inorganic salt solution, and then bipolar membrane electrodialysis is performed in the electrodialysis step S8-8, thereby recovering an inorganic acid and an alkali from the inorganic salt solution. The recovered inorganic acid and alkali are then supplied to the acid leaching step S1, the primary low pH adjustment step S3, the primary high pH adjustment step S5, the redissolution step S7-1, the secondary low pH adjustment step S7-2, the secondary high pH adjustment step S7-4, and the like, and reused, so that the amounts of the inorganic acid and alkali used in the respective steps can be reduced.

In addition, according to the cobalt recovery method of the present embodiment, since the condensed water generated in the concentration step S8-2 is used for various treatments, the condensed water can be effectively used. Furthermore, the crystals obtained in the solid-liquid separation steps S4, S6, S7-5, S8-4 and S8-6 are washed with condensed water, whereby the recovery rate of each crystal can be further improved.

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

As a modification, for example, in the embodiment of fig. 1 to 4, in order to remove the residual impurity metals dissolved in the redissolved solution obtained in the redissolved step S7-1, the redissolved solution may be supplied to the solvent extraction step S7-2 before being supplied to the secondary low pH adjustment step S7-3 as shown in fig. 9 and 10.

In the embodiment of fig. 9 and 10, the pH of the redissolution solution is preferably adjusted to 2.0 to 5.0, although not particularly limited in the redissolution step S7-1. This is because if the pH of the redissolution is too low, the extraction rate of the impurity metal in the solvent extraction in the subsequent solvent extraction step S7-2 is lowered, and if it is too high, cobalt may be extracted in the solvent extraction. The pH of the redissolution can be adjusted by adding an alkali such as sodium hydroxide, if necessary.

In the solvent extraction step S7-2, the redissolved solution is subjected to solvent extraction using an extractant, whereby the impurity metal moves to the extractant side and is separated into the extractant (organic phase) containing the impurity metal and the redissolved solution (aqueous phase) containing cobalt. Thereby enabling the removal of impurity metals from the redissolved solution.

The extractant used for solvent extraction is not particularly limited, and examples thereof include carboxylic acids such as 9, 9-dimethyldecanoic acid ("Versatic acid 10" manufactured by Shell corporation), and such extractants can be diluted with a hydrocarbon solvent in advance. The hydrocarbon solvent is not particularly limited, and examples thereof include "Isopar M" manufactured by Exxon Mobile corporation and "Solvesso 150" manufactured by Exxon Mobile corporation.

The solvent extraction method is not particularly limited, and a method generally used can be used. For example, the redissolved solution and the extractant are contacted in the extraction tank 20, and mixed by stirring for a predetermined time with a mixer or the like, thereby reacting the impurity metal ions with the extractant. The volume ratio of the extractant to the redissolution (volume of the extractant/volume of the redissolution) is not particularly limited, and is preferably set in the range of 1.0 to 10.0. The equilibrium pH at the time of solvent extraction is not particularly limited, but is preferably adjusted to 2.0 or more and 5.0 or less by adding an alkali such as sodium hydroxide. By setting the equilibrium pH to 5.0 or less, the extraction of cobalt into the extractant can be reduced, and by setting the equilibrium pH to 2.0 or more, the extraction rate of impurity metals from the extractant can be improved.

In extracting the impurity metals to the extractant by solvent extraction, the extractant and the redissolved solution mixed together are separated by a specific gravity difference, for example, using a settler. The solvent extraction may be repeated, and the number of times of extraction may be set according to the concentration of the remaining impurity metal. Further, for example, a multistage system in which the extraction agent and the redissolved solution are brought into convective contact may be employed.

The re-dissolved solution from which cobalt has been dissolved and impurity metals have been removed after the solvent extraction step S7-2 is supplied to the secondary low pH adjustment step S7-3. The steps from the secondary low pH adjustment step S7-3 to the solid-liquid separation step S7-6 are the same as the steps from the secondary low pH adjustment step S7-2 to the solid-liquid separation step S7-5 in the embodiment of FIGS. 1 to 4.

On the other hand, the extractant containing the impurity metals after the solvent extraction step S7-2 is supplied to the reverse extraction step S7-7 to recover the impurity metals. In the reverse extraction step S7-7, the extractant is subjected to reverse extraction using an inorganic acid, whereby the impurity metals move to the inorganic acid side. Thereby, the impurity metal extracted by the extractant can be reversely extracted from the extractant.

The inorganic acid used for the back extraction is not particularly limited, and for example, sulfuric acid, hydrochloric acid, or the like can be used. The method of the reverse extraction is not particularly limited, and a method generally used can be used. For example, the extractant and an aqueous solution of an inorganic acid such as an aqueous solution of sulfuric acid are contacted in the reverse extraction tank 21, and the mixture is stirred for a predetermined time by a mixer or the like. The pH of the aqueous solution of the inorganic acid is not particularly limited, but is preferably 2.0 or less.

When the impurity metals are extracted from the extractant by the reverse extraction, the extractant and the aqueous inorganic acid solution mixed together are separated by a specific gravity difference by, for example, a settler. The inorganic acid aqueous solution in which the impurity metal is dissolved after the reverse extraction step S7-7 may be subjected to neutralization treatment by adding an alkaline aqueous solution such as an aqueous sodium hydroxide solution while stirring in the neutralization tank 22, followed by solid-liquid separation such as filtration or centrifugal separation to recover the impurity metal as crystals of an inorganic salt such as a hydroxide.

The extractant from which the impurity metals have been removed after the reverse extraction step S9 is supplied to the solvent extraction step S6 (extraction tank 20) and reused as the extractant used in the solvent extraction step S6.

According to the embodiment of fig. 9 and 10, the redissolved solution in which cobalt and residual impurity metals are dissolved after the redissolved step S7-1 is subjected to extraction of the impurity metals from the redissolved solution in the solvent extraction step S7-2, and then the impurity metals are removed from the redissolved solution in the second low pH adjustment step S7-3, so that the residual impurity metals in the redissolved solution can be reduced as much as possible. Therefore, in the subsequent secondary high pH adjustment step S7-5 for recovering cobalt, cobalt can be recovered with high purity.

In the embodiment of fig. 9 and 10, the solvent extraction step S7-2 is performed after the redissolution step S7-1, but the solvent extraction step S7-4 may be performed after the precipitation step S7-3 as shown in fig. 11 and 12. In the embodiment of fig. 11 and 12, the redissolved solution as a supernatant after the precipitation step S7-3 is supplied to the solvent extraction step S7-4, and the residual impurity metals are extracted from the redissolved solution by the same method as the solvent extraction step S7-2 of the embodiment of fig. 9 and 10. The extraction agent containing the impurity metals after the solvent extraction step S7-4 is supplied to the reverse extraction step S7-7 to recover the impurity metals, and the impurity metals are reversely extracted from the extraction agent from which the impurity metals are extracted by the same method as the reverse extraction step S7-7 in the embodiment of fig. 9 and 10. The re-dissolved solution from the solvent extraction step S7-4, in which cobalt is dissolved and the impurity metals are removed, is supplied to the secondary high pH adjustment step S7-5. The steps from the secondary high pH adjustment step S7-5 to the solid-liquid separation step S7-6 are the same as those from the secondary high pH adjustment step S7-4 to the solid-liquid separation step S7-5 of the above embodiment.

According to the embodiment of fig. 11 and 12, the impurity metals are removed from the redissolved solution in the second low pH adjustment step S7-2 after the redissolved solution in which cobalt and the remaining impurity metals are dissolved after the redissolved step S7-1, and then the impurity metals are extracted from the redissolved solution in the solvent extraction step S7-2, so that the impurity metals remaining in the redissolved solution can be reduced as much as possible. Therefore, in the subsequent secondary high pH adjustment step S7-5 for recovering cobalt, cobalt can be recovered with high purity.

As another modification, in the embodiment shown in fig. 1 to 4, in order to further improve the purity of the cobalt salt crystals in the precipitate recovered in the solid-liquid separation step S7-5, the precipitate recovered in the solid-liquid separation step S7-5 may be supplied to the redissolution step S7-6 as shown in fig. 13 and 14.

In the re-dissolution step S7-6, a precipitate containing a crystal of a cobalt salt is dissolved by adding an inorganic acid. 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. The method for dissolving the precipitate is not particularly limited, and for example, a re-dissolution solution in which cobalt and a small amount of impurity metals possibly contained in the precipitate are dissolved is produced by dissolving the precipitate in an aqueous solution of an inorganic acid such as an aqueous sulfuric acid solution so as to have a desired concentration in the re-dissolution tank 23. In the redissolution step S7-6, the concentration of the inorganic acid in the aqueous solution is preferably 1mol/L to 5mol/L, and the temperature of the aqueous solution is preferably 60 ℃ or higher.

The redissolved solution obtained in the redissolution step S7-6 is supplied to the solvent extraction step S7-7, and the residual impurity metals are extracted from the redissolved solution by the same method as that of the solvent extraction step S7-2 in the embodiment of fig. 9 and 10. The extraction agent containing the impurity metal after the solvent extraction step S7-7 is supplied to the reverse extraction step S7-10 to recover the impurity metal, and the impurity metal is reversely extracted from the extraction agent from which the impurity metal has been extracted by the same method as the reverse extraction step S7-7 of the embodiment shown in fig. 9 and 10.

The re-dissolved solution from the solvent extraction step S7-7, in which cobalt is dissolved and the impurity metals are removed, is supplied to the third high pH adjustment step S7-8. In the third high pH adjustment step S7-8, the pH of the redissolution is adjusted to a range of 7 or more and 11 or less, preferably 8 or more and 10 or less, by adding an alkali to the first high pH adjustment step S5. Thus, cobalt in the redissolution is precipitated as a cobalt salt such as cobalt hydroxide in the form of crystals. In the third high pH adjustment step S7-8, in addition to cobalt, a valuable metal such as nickel or manganese may be precipitated in the form of crystals of an inorganic salt such as a hydroxide. As the base used for pH adjustment, for example, sodium hydroxide, potassium hydroxide, lithium hydroxide, or the like can be used, and in the present embodiment, sodium hydroxide is used from the viewpoint of low cost and easy handling.

The method for adjusting the pH of the redissolution in the third high pH adjustment step S7-8 is not particularly limited, and a method generally used can be used. Examples thereof include: a method of adding an aqueous alkali solution such as an aqueous sodium hydroxide solution while stirring the redissolved solution in the high pH adjustment tank 23 three times. When adjusting the pH, the redissolved solution is preferably warmed to a constant temperature, for example, in the range of 30 ℃ to 60 ℃. The aqueous alkali solution to be added to the redissolution is not particularly limited, and the alkali concentration is preferably 1.0mol/L or more.

The redissolved solution after the third high pH adjustment step S7-8 is supplied to a solid-liquid separation step S7-9 (corresponding to the "third cobalt separation step" described in the claims). In the solid-liquid separation step S7-9, precipitates including crystals of a cobalt salt and the like precipitated in the third high pH adjustment step S7-8 are separated from the redissolved solution by using the solid-liquid separator 24. Thus, cobalt dissolved in the redissolution can be recovered as a cobalt salt.

The precipitate recovered in the solid-liquid separation step S7-9 is washed with a washing liquid. The washed waste washing liquid is preferably supplied to the impurity removal step S8-1 together with the redissolved solution. Thus, lithium contained in the re-dissolving liquid or the waste washing liquid can be supplied to the carbonation step S8-5, and lithium can be recovered at a high recovery rate by carbonation in the carbonation step S8-5. The water used for washing the precipitate is not particularly limited, and condensed water generated in the concentration step S8-2 is preferably used, whereby the condensed water can be effectively used.

As another modification, in the embodiment of fig. 1 to 4, the impurity removal step S8-1 for removing at least calcium and/or magnesium is performed on the liquid to be treated before the concentration step S8-2, but instead of this step or in addition to this step, 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 S8-8. The same modifications can be made to any of the above embodiments.

As another modification, in the embodiment of fig. 1 to 4, a treatment step for removing impurities such as silicon contained in the inorganic salt solution may be performed after the dissolution step S8-7 and before the electrodialysis step S8-8. This treatment step may be performed in place of the impurity removal step S8-1 or in addition to the impurity removal step S8-1. As an example of this treatment step, an inorganic salt (sodium sulfate in the present embodiment) contained in an inorganic salt solution is recrystallized by evaporation, concentration, or the like, and then crystals of the inorganic salt are separated into solid and liquid, and recovered from an aqueous solution containing the crystals of the inorganic salt. The crystals of the recovered inorganic salt are then dissolved, for example with water, to regenerate the inorganic salt solution. The regenerated inorganic salt solution is supplied to the electrodialysis step S8-8.

In this embodiment, by removing silicon contained in the inorganic salt solution before the electrodialysis step S8-8, the amount of impurities in the inorganic solution subjected to electrodialysis in the electrodialysis step S8-8 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 S8-8 is supplied to the evaporation concentration device 13 and evaporation concentration is performed again in the concentration step S8-2, the amount of impurities in the desalted solution is reduced, whereby the generation and adhesion of scale on the heat transfer surface of the heat exchanger of the evaporation concentration device 13 in the concentration step S8-2 can be suppressed. Further, since the amount of impurities in the liquid to be treated obtained in the solid-liquid separation step S8-6 after the carbonation step S8-5 is reduced, most of the liquid to be treated after the solid-liquid separation step S8-6 can be circulated again in the system. Therefore, lithium remaining in the liquid to be treated after the solid-liquid separation step S8-6 can be more sufficiently recovered, and therefore lithium can be recovered at a high recovery rate. It should be noted that the same changes can be made to any of the above embodiments.

As another modification, in the embodiment of fig. 1 to 4, as shown in fig. 15 and 16, a firing step S0 for firing the spent lithium ion batteries may be further included before the acid leaching step S1. The method for firing the spent lithium ion battery in the firing step S0 is not particularly limited, and a known firing apparatus 25 may be used.

In the embodiment shown in fig. 15 and 16, the off-gas generated in the baking device 25 (baking step S0) is supplied to the carbonation step S8-5 (carbonation tank 16), and the off-gas is mixed into the liquid to be treated as carbon dioxide in the carbonation step S8-5. This can reduce the amount of carbon dioxide used in the carbonation step S8-5. In the carbonation step S8-5, the temperature of the liquid to be treated may be raised. It should be noted that the same changes can be made to any of the above embodiments.

As another modification, in the embodiment of fig. 1 to 4, the method of recovering lithium in the impurity removal step S8-1 and the subsequent steps is not particularly limited, and various methods can be used. It should be noted that similar modifications can be made to any of the above embodiments.

As another modification, a case of recovering cobalt from the waste lithium ion battery is exemplified in the embodiments of fig. 1 to 4, but the present disclosure is not limited to a method for recovering cobalt from the waste lithium ion battery. It should be noted that the same changes can be made to any of the above embodiments.

[ cobalt recovery method according to the second embodiment ]

When cobalt is recovered from a waste lithium ion battery, if the waste lithium ion battery contains impurity metals such as iron, aluminum, and copper, these impurity metals are dissolved in a treatment liquid by acid leaching. Thus, since the impurity metals are mixed into the cobalt as the target recovered material to deteriorate the quality, it is necessary to remove the impurity metals when the liquid to be treated contains the impurity metals. As a method for removing copper in impurity metals, for example, patent document 2 discloses a method for separating copper from a liquid to be treated by subjecting the liquid to be treated, which is obtained by leaching a waste lithium ion battery with an acid, to solvent extraction. However, the method described in patent document 2 is a method of solvent extraction of all of the liquid to be treated obtained by leaching the spent lithium ion battery with an acid. Therefore, a large amount of an extractant for solvent extraction of a liquid to be treated is required, and when the amount of the extractant increases with the amount of the spent lithium ion battery and the amount of acid used in acid leaching, the cost of the extractant is very high and uneconomical. The cobalt recovery method according to the second aspect is made to solve the above problem, and an object thereof is to provide a cobalt recovery method capable of recovering cobalt from a liquid to be treated in which at least cobalt and copper are dissolved, with high purity and at low cost.

Patent document 2: japanese unexamined patent publication No. 2014-162982

A cobalt recovery method according to a second aspect of the present disclosure is characterized by including the steps of: a primary pH adjustment step of adjusting the pH to 7 or more by adding an alkali to an acidic treatment target solution in which at least cobalt and copper are dissolved; a primary cobalt separation step of separating a precipitate containing crystals of a cobalt salt and crystals of a copper salt precipitated in the primary pH adjustment step from the liquid to be treated; a re-dissolving step of adding an inorganic acid to dissolve the precipitate separated in the primary cobalt separation step; a solvent extraction step of subjecting the redissolved solution obtained in the redissolving step to solvent extraction using an extractant to separate copper from the redissolved solution; a secondary pH adjustment step of adjusting the pH to 7 or more by adding an alkali to the redissolved solution after the solvent extraction step; and a secondary cobalt separation step of separating a precipitate containing a crystal of the cobalt salt precipitated in the secondary pH adjustment step from the redissolved solution.

The cobalt recovery process described in paragraph 0122 can be constructed in the following manner: further comprising a reverse extraction step of performing reverse extraction using an inorganic acid on the extractant from which copper has been extracted after the solvent extraction step, separating copper from the extractant, and reusing the extractant after the reverse extraction step as the extractant used in the solvent extraction step.

Additionally, the cobalt recovery process described in paragraph 0122 or paragraph 0123 can be constructed in the following manner: further comprising an acid leaching step of leaching the spent lithium ion battery with an inorganic acid to dissolve cobalt and copper, thereby obtaining the liquid to be treated.

Additionally, the cobalt recovery process of any of paragraphs 0122 to 0124 may be constructed in the following manner: in the primary pH adjustment step, an alkali is added to the treatment target liquid to adjust the pH to 4 or more and 7 or less, and an alkali is added to the treatment target liquid from which the precipitate precipitated is separated to adjust the pH to 7 or more.

The cobalt recovery method according to any one of paragraphs 0122 to 0125 may be configured to dissolve lithium in the treatment target solution, and further include: a concentration step of evaporating and concentrating the treated liquid after the primary cobalt separation step; 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 lithium separation step of separating a precipitate containing crystals of lithium carbonate precipitated in the carbonation step from the liquid to be treated.

According to the cobalt recovery method of the second aspect of the present disclosure, the treatment target solution in which at least cobalt and copper are dissolved is first subjected to pH adjustment to 7 or more by adding an alkali in the primary pH adjustment step, thereby recovering cobalt from the treatment target solution as a cobalt salt, then the recovered cobalt salt is dissolved with an inorganic acid in the redissolution step, and the redissolved solution in which cobalt is redissolved is subjected to solvent extraction in the solvent extraction step, thereby separating copper contained in the redissolved solution from the redissolved solution. The amount of the inorganic acid used in the redissolution solution is an amount sufficient to dissolve the cobalt salt recovered from the solution to be treated in the primary pH adjustment step and less than the amount of the inorganic acid used in the solution to be treated to dissolve the metal such as cobalt. In particular, when the liquid to be treated is a liquid obtained by acid leaching of waste lithium ion batteries, the amount of the waste lithium ion batteries to be dissolved is large, and therefore, a large amount of the inorganic acid is required for the acid leaching, and the amount of the liquid to be treated is also large. Therefore, by once removing cobalt from the liquid to be treated and then dissolving cobalt again with the inorganic acid as in the cobalt recovery method according to the second aspect of the present disclosure, the amount of the re-dissolved liquid in which cobalt is dissolved can be significantly reduced as compared with the amount of the first liquid to be treated. When the amount of the re-dissolved solution is reduced, the amount of the extractant used for solvent extraction for separating impurity metals such as copper can be reduced, and therefore the cost of the extractant can be reduced. Further, since impurity metals such as copper are removed from the redissolved solution by solvent extraction, cobalt can be recovered with high purity. As described above, the cobalt recovery method according to the second aspect of the present disclosure can recover cobalt from a treatment target liquid in which cobalt and copper are dissolved, with high purity and at low cost.

Fig. 17 shows the steps of each step in the embodiment of the cobalt recovery method according to the second embodiment of the present disclosure, and fig. 18 shows a schematic configuration of a treatment apparatus for carrying out the cobalt recovery method according to the present embodiment. The cobalt recovery method according to the present embodiment can be suitably used for recovering cobalt from an acidic treatment solution containing at least cobalt and copper as an impurity metal, and particularly can be suitably used for recovering cobalt from a waste lithium ion battery. The following description will be given by taking an example of recovering cobalt from a waste lithium ion battery and further recovering lithium.

The cobalt recovery method of the present embodiment includes the steps of:

an acid leaching step S1 of leaching the spent lithium ion battery with an inorganic acid to dissolve cobalt and copper and further dissolve at least lithium;

a solid-liquid separation step S2 of separating an insoluble residue from the acidic liquid to be treated in which at least cobalt, copper, and lithium are dissolved, which is obtained in the acid leaching step S1;

a primary pH adjustment step S3 of adding an alkali to the liquid to be treated from which the insoluble residue has been removed after the solid-liquid separation step S2 to adjust the pH to 7 or more;

a solid-liquid separation step S4 of separating a precipitate containing crystals of the cobalt salt and the copper salt precipitated in the primary pH adjustment step S3 from the liquid to be treated (primary cobalt separation step);

a re-dissolution step S5 of dissolving the precipitate separated in the solid-liquid separation step S4 by adding an inorganic acid;

a solvent extraction step S6 of extracting the re-dissolved solution obtained in the re-dissolving step S5, in which at least cobalt and copper are dissolved, with a solvent using an extraction agent, and separating copper from the re-dissolved solution;

a secondary pH adjustment step S7 of adding an alkali to the copper-removed redissolved solution after the solvent extraction step S6 to adjust the pH to 7 or more;

a solid-liquid separation step S8 of separating a precipitate containing crystals of a cobalt salt precipitated in the secondary pH adjustment step S7 from the redissolved solution (secondary cobalt separation step); and (c) a second step of,

a reverse extraction step S9 of separating copper from the extractant by performing reverse extraction using an inorganic acid on the extractant from which copper has been extracted after the solvent extraction step S6.

an impurity removal step S10 of chelating the treatment target liquid from which the precipitate has been removed and in which lithium and an inorganic salt have been dissolved after the solid-liquid separation step S4;

a concentration step S11 of evaporating and concentrating the liquid to be treated after the impurity removal step S10;

a crystallization step S12 of cooling and crystallizing the liquid to be treated after the concentration step S11 to precipitate an inorganic salt in a crystal form;

a solid-liquid separation step S13 of separating a precipitate containing crystals of the inorganic salt precipitated in the crystallization step S12 from the liquid to be treated;

a carbonation step S14 of mixing carbon dioxide and/or adding a water-soluble carbonate to the treated liquid from which the precipitates have been removed after the solid-liquid separation step S13;

a solid-liquid separation step S15 (corresponding to the "lithium separation step" described in the claims) of separating a precipitate containing crystals of lithium carbonate precipitated in the carbonation step S14 from the liquid to be treated;

a dissolution step S16 of dissolving the precipitate containing the crystals of the inorganic salt separated in the solid-liquid separation step S13 with water; and the number of the first and second groups,

an electrodialysis step S17 of subjecting the inorganic salt solution obtained in the dissolving step S16, in which the inorganic salt is dissolved, to bipolar membrane electrodialysis to separate the alkali and the inorganic acid from the inorganic salt solution.

The waste lithium ion battery to be recovered with cobalt is the same as in the cobalt recovery method of the first embodiment described above, and a detailed description thereof is omitted here.

First, in the acid leaching step S1, the spent lithium ion battery is leached with an inorganic acid. Thereby dissolving valuable metals such as cobalt and lithium contained in the waste lithium ion battery. In this acid leaching, in addition to valuable metals, impurity metals such as copper are also dissolved. Examples of the inorganic acid include sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid, 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 for leaching the spent lithium ion battery with the inorganic acid is not particularly limited, and a commonly used method can be used. For example, in the acid leaching tank 1, 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 to obtain a solution to be treated in which the above metals such as cobalt, lithium, and copper are dissolved. In the acid leaching step S1, the concentration of the inorganic acid in the aqueous solution is preferably 1mol/L to 5mol/L, and the temperature of the aqueous solution is preferably 60 ℃ or higher.

The liquid to be treated obtained in the acid leaching step S1 is supplied to a solid-liquid separation step S2. In the solid-liquid separation step S2, insoluble residues are separated from the liquid to be treated using a solid-liquid separator. The insoluble residue is a carbon material, a metal material, an organic material, which is mainly insoluble in an inorganic acid, contained in the waste lithium ion battery. 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 a known solid-liquid separation apparatus such as a centrifugal separation apparatus of a decantation type can be used. The same applies to the following solid-liquid separation steps S4, S8, S13, S15, and the like.

The liquid to be treated after the solid-liquid separation step S2 is supplied to the primary pH adjustment step S3. In the primary pH adjustment step S3, a base is added to the liquid to be treated to adjust the pH to 7 or more, preferably 7 or more and 13 or less, more preferably 7 or more and 11 or less, and still more preferably 8 or more and 10 or less. As a result, cobalt in the liquid to be treated precipitates in the form of crystals of cobalt salts such as cobalt hydroxide, and copper precipitates in the form of crystals of copper salts such as copper hydroxide, and is removed from the liquid to be treated. In the primary pH adjustment step S3, in addition to cobalt and copper, valuable metals such as nickel and manganese and/or impurity metals such as iron and aluminum are precipitated in the form of crystals of inorganic salts such as hydroxides, and can be removed from the liquid to be treated. As the base used for pH adjustment, for example, sodium hydroxide, potassium hydroxide, lithium hydroxide, or the like can be used, and in the present embodiment, sodium hydroxide is used from the viewpoint of low cost and easy handling.

The method for adjusting the pH of the liquid to be treated in the primary pH adjustment step S3 is not particularly limited, and a commonly performed method can be used. Examples thereof include: a method of adding an aqueous alkali solution such as an aqueous sodium hydroxide solution while stirring the treatment liquid in the primary pH adjusting tank 2. In the pH adjustment, the temperature of the liquid to be treated is preferably raised to a constant temperature in the range of, for example, 30 ℃ to 80 ℃. The aqueous alkali solution to be added to the liquid to be treated is not particularly limited, but the alkali concentration is preferably 0.2mol/L or more.

The liquid to be treated after the primary pH adjustment step S3 is supplied to the solid-liquid separation step S4. In the solid-liquid separation step S4, precipitates including crystals of a cobalt salt, crystals of a copper salt, and the like precipitated in the primary pH adjustment step S3 are separated from the treatment target liquid by using a solid-liquid separator. The precipitate recovered in the solid-liquid separation step S4 is washed with a washing liquid. The washing waste liquid after washing is preferably supplied to the impurity removal step S10 together with the liquid to be treated. Thus, lithium contained in the waste cleaning solution can be supplied from the impurity removal step S10 to the carbonation step S14 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 S14. The water used for washing the precipitates is not particularly limited, but condensed water generated when the liquid to be treated is concentrated by evaporation in the concentration step S11 is preferably used, whereby the condensed water can be effectively used.

The precipitate recovered in the solid-liquid separation step S4 contains impurity metals such as copper in addition to cobalt. Therefore, the precipitate recovered in the solid-liquid separation step S4 is supplied to the re-dissolution step S5 in order to remove the impurity metal such as copper.

In the redissolution step S5, the precipitate including the crystal of the cobalt salt and the crystal of the copper salt is dissolved by adding the inorganic acid. 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. The method for dissolving the precipitate is not particularly limited, and for example, a redissolution in which cobalt, copper, or the like is dissolved is obtained by dissolving the precipitate in an aqueous solution of an inorganic acid such as an aqueous sulfuric acid solution so as to have a desired concentration in the redissolution tank 3. In the redissolution step S5, the concentration of the inorganic acid in the aqueous solution is preferably 1mol/L to 5mol/L, and the temperature of the aqueous solution is preferably 30 ℃ or higher. If the pH of the redissolution is too low, the extraction rate of impurity metals such as copper is lowered in the solvent extraction in the subsequent solvent extraction step S6, and if it is too high, cobalt may be extracted in the solvent extraction. Therefore, it is preferable to adjust the pH of the redissolution to 2.0 or more and 5.0 or less by adding an alkali such as sodium hydroxide if necessary.

The redissolved solution obtained in the redissolution step S5 is supplied to the solvent extraction step S6. In the solvent extraction step S6, the redissolved solution is subjected to solvent extraction using an extractant, whereby the impurity metal such as copper moves to the extractant side, and is separated into the extractant (organic phase) containing the impurity metal such as copper and the redissolved solution (aqueous phase) containing cobalt. This enables the removal of impurity metals such as copper from the redissolved solution.

The extractant used for solvent extraction is not particularly limited, and examples thereof include carboxylic acids such as 9, 9-dimethyldecanoic acid ("Versatic acid 10" manufactured by Shell corporation), and such extractants can be diluted with a hydrocarbon solvent in advance. The hydrocarbon solvent is not particularly limited, and examples thereof include "Isopar M" manufactured by Exxon Mobile and "Solvesso 150" manufactured by Exxon Mobile.

The solvent extraction method is not particularly limited, and a method generally used can be used. For example, the redissolved solution and the extractant are contacted in the extraction tank 4, and mixed by stirring for a predetermined time with a mixer or the like, thereby reacting the ion of the impurity metal such as copper with the extractant. The volume ratio of the extractant to the redissolution (volume of the extractant/volume of the redissolution) is not particularly limited, and is preferably set in the range of 1.0 to 10.0. The equilibrium pH at the time of solvent extraction is not particularly limited, but is preferably adjusted to 2.0 or more and 5.0 or less by adding an alkali such as sodium hydroxide. By setting the equilibrium pH to 5.0 or less, the extraction of cobalt into the extractant can be reduced, and by setting the equilibrium pH to 2.0 or more, the extraction rate of impurity metals such as copper from the extractant can be improved.

When extracting an impurity metal such as copper by solvent extraction to an extractant, the extractant and a redissolution mixed together are separated by a specific gravity difference using, for example, a settler. The solvent extraction may be repeated, and the number of times of extraction may be determined according to the concentration of the remaining impurity metal such as copper. Further, for example, a multistage system in which the extraction agent and the redissolved solution are brought into convective contact may be employed.

The re-dissolved solution from the solvent extraction step S6, in which cobalt is dissolved and impurity metals such as copper are removed, is supplied to the secondary pH adjustment step S7. In the secondary pH adjustment step S7, as in the primary pH adjustment step S3, a base is added to the redissolution to adjust the pH to a range of 7 or more, preferably 7 or more and 13 or less, more preferably 7 or more and 11 or less, and still more preferably 8 or more and 10 or less. Thus, cobalt in the redissolution precipitates in the form of a crystal of a cobalt salt such as cobalt hydroxide. In the secondary pH adjustment step S7, in addition to cobalt, valuable metals such as nickel and manganese may be precipitated in the form of crystals of inorganic salts such as hydroxides. As the base used for pH adjustment, for example, sodium hydroxide, potassium hydroxide, lithium hydroxide, or the like can be used as in the primary pH adjustment step S3, but in the present embodiment, sodium hydroxide is used from the viewpoint of low cost and easy handling.

The method for adjusting the pH of the redissolution in the secondary pH adjustment step S7 is not particularly limited, and a commonly performed method can be used. Examples thereof include: a method of adding an aqueous alkali solution such as an aqueous sodium hydroxide solution while stirring the redissolved solution in the secondary pH adjustment tank 5. When the pH is adjusted, the temperature of the redissolved solution is preferably raised to a constant temperature, for example, in the range of 30 ℃ to 80 ℃. The aqueous alkali solution to be added to the redissolution is not particularly limited, but the alkali concentration is preferably 0.2mol/L or more.

The redissolved solution after the secondary high pH adjustment step S7 is supplied to the solid-liquid separation step S8. In the solid-liquid separation step S8, a precipitate containing crystals of a cobalt salt and the like precipitated in the secondary pH adjustment step S7 is separated from the redissolved solution by using a solid-liquid separator. In this way, cobalt dissolved in the redissolution can be precipitated as a cobalt salt and recovered.

The precipitate recovered in the solid-liquid separation step S8 is washed with a washing liquid. The washing waste liquid after washing is preferably supplied to the impurity removal step S10 together with the redissolved solution. Thus, lithium contained in the re-solution or the waste washing liquid can be concentrated in the concentration step S11 and then supplied to the carbonation step S14, and lithium can be recovered at a high recovery rate by carbonation in the carbonation step S14. The water used for washing the precipitates is not particularly limited, and condensed water generated in the concentration step S11 is preferably used, whereby the condensed water can be effectively used. In the present embodiment, the waste washing liquid after washing is supplied to the impurity removal step S10 together with the redissolved solution, and thus when the waste washing liquid or the redissolved solution contains calcium and/or magnesium, these are removed in the impurity removal step S10, but when the waste washing liquid or the redissolved solution does not contain calcium and/or magnesium, the liquid can be supplied to the concentration step S11. The washing waste liquid and the redissolution liquid may be supplied to the primary pH adjustment step S3. Therefore, when cobalt is not precipitated in the secondary pH adjustment step S7 and remains in the redissolved solution, the recovery rate of cobalt can be improved.

On the other hand, the extractant containing the impurity metal such as copper after the solvent extraction step S6 is supplied to the reverse extraction step S9 to recover the impurity metal such as copper. In the reverse extraction step S9, the extractant is subjected to reverse extraction using an inorganic acid, whereby the impurity metal such as copper moves to the inorganic acid side. This enables the extraction of the impurity metals such as copper extracted by the extractant from the extractant by reverse extraction.

The inorganic acid used for the back extraction is not particularly limited, and for example, sulfuric acid, hydrochloric acid, or the like can be used. The method of the reverse extraction is not particularly limited, and a method generally used can be used. For example, the extractant and an aqueous solution of an inorganic acid such as an aqueous solution of sulfuric acid are contacted in the reverse extraction tank 6, and stirred for a predetermined time by a mixer or the like to be mixed. The pH of the aqueous solution of the inorganic acid is not particularly limited, but is preferably 2.0 or less.

In the reverse extraction of an impurity metal such as copper from an extractant by reverse extraction, the extractant and an aqueous inorganic acid solution mixed together are separated by a difference in specific gravity, for example, by a settler. The inorganic acid aqueous solution in which the impurity metal such as copper is dissolved after the reverse extraction step S9 may be subjected to neutralization treatment by adding an alkaline aqueous solution such as an aqueous sodium hydroxide solution while stirring in the neutralization tank 7, followed by solid-liquid separation such as filtration or centrifugal separation to recover the impurity metal such as copper as crystals of an inorganic salt such as a hydroxide.

The extractant from which the impurity metal such as copper has been removed after the reverse extraction step S9 is supplied to the solvent extraction step S6 (extraction tank 4) and reused as the extractant used in the solvent extraction step S6.

Next, in addition to lithium, an inorganic salt (sodium sulfate in the present embodiment) is dissolved in the liquid to be treated after the solid-liquid separation step S4 by the inorganic acid (sulfuric acid in the present embodiment) and the alkali (sodium hydroxide in the present embodiment) added in the acid leaching step S1 and the primary pH adjustment step S3. In addition, impurities such as calcium, magnesium, and silicon are generally dissolved in the liquid to be treated. The following describes a method for recovering lithium in a liquid to be treated.

The liquid to be treated after the solid-liquid separation step S4 is supplied to the impurity removal step S10. In the impurity removal step S10, at least polyvalent cations such as calcium and/or magnesium contained in the liquid to be treated are removed. By removing calcium, magnesium, and the like contained as impurities in the liquid to be treated, it is possible to suppress the formation and adhesion of scale on the heat transfer surface of the heat exchanger of the evaporation and concentration apparatus 9 in the subsequent concentration step S11, and it is possible to maintain the heat exchange efficiency at a high level. When the treatment target liquid contains calcium, magnesium, or the like, polyvalent cations such as calcium, magnesium, or the like contained in the inorganic solution may precipitate in the cation exchange membrane of the bipolar membrane electrodialysis device 13 in the electrodialysis step S17, thereby deteriorating the membrane performance. Therefore, by removing in advance substances such as calcium and magnesium that cause problems such as scaling during the electrodialysis operation from the liquid to be treated, it is possible to prevent adverse effects on the cation exchange membrane of the bipolar membrane electrodialysis device 13 and maintain the performance of electrodialysis high.

The method for removing calcium and magnesium from the treatment target liquid in the impurity removal step S10 is not particularly limited, and, for example, the polyvalent cation removal device 8 can be used. The polyvalent cation removal device 8 is a device for removing polyvalent cations having a valence of 2 or more, such as calcium ions and magnesium ions, and may be, for example, a device having an ion exchange resin therein and configured to be capable of adsorbing calcium ions and magnesium ions when the liquid to be treated contacts the ion exchange resin. As the polyvalent cation removal device 8, a device having a configuration capable of introducing the liquid to be treated into a column filled with a chelate resin may be exemplified. As the chelate resin, a resin capable of selectively capturing calcium ions and magnesium ions can be used, and examples thereof include iminodiacetic acid type and aminophosphoric acid type. The polyvalent cation removal device 8 may be a device to which a chelating agent is added. In the impurity removal step S10, the impurities removed from the treatment liquid include silicon (silicate ions) in addition to calcium and magnesium.

The liquid to be treated after the impurity removal step S10 is supplied to the concentration step S11. In the concentration step S11, the liquid to be treated is heated to be evaporated and concentrated, i.e., the water in the liquid to be treated is evaporated, thereby concentrating 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 S14 described later.

In the concentration step S11, the liquid to be treated is preferably evaporated and concentrated to such a concentration that lithium is not precipitated in the concentrated liquid to be treated in a crystal form of a lithium salt such as lithium sulfate, for example. This can increase the lithium concentration in the concentrated liquid to be treated, and can increase the recovery rate of lithium carbonate in the carbonation step S14.

When the precipitate is precipitated in the concentration step S11, a solid-liquid separation step of separating the precipitate from the liquid to be treated may be performed.

In the concentration step S11, the method of evaporating and concentrating the liquid to be treated is not particularly limited, and, for example, the evaporation and concentration apparatus 9 may be used. The evaporation concentration device 9 is not particularly limited as long as it can concentrate the liquid to be treated by evaporation, and a known evaporation concentration device such as a heat pump type, an ejector (injector) drive type, a steam type, or a flash evaporation type may 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 9 is connected to a vacuum pump, not shown, to maintain the inside at a low pressure, and in the concentration step S11, it is preferable to perform evaporation and concentration by heating the liquid to be treated at a low pressure lower than the atmospheric pressure. Since 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, the energy required for evaporation and concentration of the liquid to be treated can be suppressed to be low by performing evaporation and concentration at low pressure, and energy saving can be achieved.

In the concentration step S11, the evaporation concentration is not necessarily performed by heating the treatment target liquid at a low pressure lower than the atmospheric pressure, and for example, the evaporation concentration may be performed by heating the treatment target liquid at the atmospheric pressure.

The liquid to be treated after the concentration step S11 is supplied to the crystallization step S12. In the crystallization step S12, the liquid to be treated is cooled and crystallized. In the crystallization step S12, the temperature of the liquid to be treated is lowered to lower the solubility until the inorganic salt contained in the liquid to be treated is crystallized, whereby the concentration of the inorganic salt (sodium sulfate in the present embodiment) in the liquid to be treated can be lowered. Therefore, when lithium carbonate is recovered in the carbonation step S14, the purity of lithium carbonate can be improved.

In the crystallization step S12, a method for cooling and crystallizing the liquid to be treated is not particularly limited, and, for example, the cooling and crystallizing device 10 may be used. The cooling crystallization apparatus 10 is an apparatus for cooling a supplied liquid to be treated in a crystallization tank to precipitate crystals of a target inorganic salt. As the cooling crystallization apparatus 10, for example, a known cooling crystallization apparatus having a cooling system such as a jacket, a crystallization apparatus using an internal coil, or an external circulation cooling type crystallization apparatus can be used, and is not particularly limited.

In the crystallization step S12, the saturation solubility is usedAnd the temperature dependence of solubility differs depending on the inorganic salt, and only crystals of the target inorganic salt are precipitated. 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) ₂ SO ₄ ·10H ₂ O) is precipitated.

The liquid to be treated after the crystallization step S12 is supplied to the solid-liquid separation step S13. In the solid-liquid separation step S13, a precipitate containing crystals of an inorganic salt (sodium sulfate in the present embodiment) is separated from the liquid to be treated by using a solid-liquid separator.

The liquid to be treated after the solid-liquid separation step S13 is supplied to the carbonation step S14. In the carbonation step S14, 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 removed, thereby precipitating lithium in the treatment target liquid in the form of 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 S14, carbon dioxide is preferably mixed into the liquid to be treated to precipitate crystals of lithium carbonate. In this way, the use of a material containing no alkali metal such as sodium in the carbonation step S14 can suppress the incorporation of alkali metals other than lithium into the precipitated crystals of lithium carbonate. Thus, lithium carbonate having high purity can be recovered.

In the carbonation step S14, 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 11, 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 treatment target liquid in a carbon dioxide atmosphere.

Since the solubility of lithium carbonate decreases as the temperature increases, the temperature of the treatment target liquid is preferably increased in the carbonation step S14. This reduces the solubility of lithium carbonate generated by the reaction between lithium and carbon dioxide in the treatment target liquid, thereby increasing 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 precipitation of crystals of the inorganic salt together with crystals of lithium carbonate, and therefore, when lithium carbonate is recovered in the carbonation step S14, the purity of lithium carbonate can be increased.

The method for raising the temperature of the liquid to be treated in the carbonation step S14 is not particularly limited, and a method for heating the liquid to be treated in the carbonation tank 11 by a known heating device such as a heater may be used. The following embodiments may be applied: before the liquid to be treated is supplied to the carbonating tank 11, the temperature of the liquid to be treated is raised in advance by using a preheating means such as a heat exchanger.

The liquid to be treated after the carbonation step S14 is supplied to the solid-liquid separation step S15. In the solid-liquid separation step S15, a precipitate containing crystals of lithium carbonate is separated from the liquid to be treated by using a solid-liquid separator. The precipitate recovered from the liquid to be treated is washed with water or the like to remove impurities, whereby the purity of lithium carbonate can be improved. The water used for washing the precipitates is not particularly limited, and condensed water generated in the concentration step S11 is preferably used, whereby the condensed water can be effectively used.

The liquid to be treated after the solid-liquid separation step S15 is not particularly limited, but it preferably contains impurities, and a part of the liquid is discharged as a discharge 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 also preferable that the washing waste liquid after washing the precipitate containing the crystals of lithium carbonate is circulated again in the system together with the liquid to be treated after the solid-liquid separation step S15.

When the liquid to be treated after the solid-liquid separation step S15 is circulated again in the system, it is preferably supplied to the concentration step S11 (evaporation and concentration apparatus 9) to be evaporated and concentrated, and preferably supplied to the primary pH adjustment step S3 (primary pH adjustment tank 2). Since the liquid to be treated after the solid-liquid separation step S15 is alkaline, it can be used as the alkali to be added in the primary pH adjustment step S3. Further, when the liquid to be treated after the solid-liquid separation step S15 contains a large amount of carbonate ions (CO) ₃ ^2- ) Then, crystals of carbonate are precipitated on the heat-conducting surface of the heat exchanger of the evaporation and concentration apparatus 9 at the time of evaporation and concentration in the concentration step S11. Here, the liquid to be treated supplied to the primary pH adjustment step S3 after the solid-liquid separation step S2 is acidic, and thus the liquid to be treated after the solid-liquid separation step S15 is neutralized with the acidic liquid to be treated, and carbonate ions are released as carbon dioxide, whereby it is possible to prevent crystals of carbonate from precipitating on the heat transfer surface of the heat exchanger of the evaporation and concentration apparatus 9 in the concentration step S11.

On the other hand, crystals of an inorganic salt (sodium sulfate in the present embodiment) contained in the precipitate precipitated in the concentration step S11 and recovered in the solid-liquid separation step S13 are supplied to the dissolution step S16. The dissolving step S16 is not particularly limited, and for example, an inorganic salt solution is obtained by dissolving crystals of an inorganic salt with, for example, water so as to form a desired concentration in the dissolving tank 18. 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, and condensed water generated in the concentration step S11 is preferably used, whereby the condensed water can be effectively used.

The inorganic salt solution obtained in the dissolving step S16 is supplied to the electrodialysis step S17. The electrodialysis step S17 is not particularly limited, and for example, the base and the inorganic acid are separated and recovered from the inorganic salt solution by the bipolar membrane electrodialysis device 13. As the bipolar membrane electrodialysis device 13, for example, a bipolar membrane electrodialysis device of a three-compartment cell system shown in fig. 20, in which a plurality of cells 130 are laminated, the cells 130 having an anion exchange membrane 131, a

cation exchange membrane

132, and 2

bipolar membranes

133 and 134 between an anode 135 and a cathode 136, can be suitably used. In the bipolar membrane electrodialysis device 13 of the present embodiment, a desalting compartment R1 is formed by the anion exchange membrane 131 and the cation exchange membrane 132, an acid compartment R2 is formed between the anion exchange membrane 131 and one bipolar membrane 133, and an alkali compartment R3 is formed between the cation exchange membrane 132 and the other bipolar membrane 134. An anode chamber R4 and a cathode chamber R5 are formed outside

bipolar membranes

133 and 134, respectively, and an anode 135 is disposed in anode chamber R4 and a cathode 136 is disposed in cathode chamber R5.

In the electrodialysis step S17, an inorganic salt solution is introduced into the desalting compartment R1, and pure water is introduced into the acid compartment R2 and the alkali compartment R3, respectively. 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 the cation exchange membrane 132, sulfate ion (SO) ₄ ^2- ) Through an anion exchange membrane 131. 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 133 and 134 ⁺ ) And hydroxide ion (OH) ^- ) Hydrogen ion (H) in acid chamber R2 ⁺ ) With sulfate ions (SO) ₄ ^2- ) Combine to form sulfuric acid (H) ₂ SO ₄ ) In the alkaline chamber R3, hydroxide ion (OH) ^- ) With sodium ion (Na) ⁺ ) Binding to form sodium hydroxide (NaOH). Thus, sulfuric acid (H) as an inorganic acid is recovered from the acid chamber R2 ₂ SO ₄ ) Sodium hydroxide (NaOH) is recovered as a base from the base chamber R3. The condensed water generated in the concentration step S11 can be used as the pure water introduced into the acid chamber R2 and the alkali chamber R3.

The desalted dilute inorganic salt solution (desalted solution) 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 S11 (evaporation and concentration device 9) because a small amount of lithium is contained, and to carbonate the dilute inorganic salt solution in the carbonation step S14 after the re-concentration. Thus, lithium can be recovered at a high recovery rate. Although the desalted liquid is supplied to the concentration step S11 in the present embodiment, the desalted liquid may be supplied to the impurity removal step S10 when calcium and/or magnesium remain in the desalted liquid. Thus, calcium and magnesium can be removed from the desalted liquid and then supplied to the concentration step S11. The desalting solution may be supplied to the primary 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 step S1 (acid leaching tank 1) and/or the redissolution step S5 (redissolution tank 3) and reused as the inorganic acid for acid leaching of the spent lithium ion battery and redissolution of a cobalt salt or the like. Further, it is preferably supplied to the impurity treatment step S10 (polyvalent cation removal device 8) and reused as a regenerated liquid of a chelate resin or an ion exchange resin.

The alkali (sodium hydroxide in the present embodiment) recovered from the alkali chamber R3 is not particularly limited, but is preferably supplied to the primary pH adjustment step S3 (primary low pH adjustment tank 2) and/or the secondary pH adjustment step S7 (secondary pH adjustment tank 5) and reused as the alkali for adjusting the pH of the liquid to be treated or the redissolved solution. Further, it is preferably supplied to the impurity treatment step S10 (polyvalent cation removal device 8) and reused as a regenerant for a chelate resin or an ion exchange resin.

In the cobalt recovery method according to the present embodiment, the treatment target liquid in which at least cobalt and copper are dissolved is first adjusted to pH 7 or more by adding an alkali in the primary pH adjustment step S3 to recover cobalt from the treatment target liquid as a cobalt salt, the recovered cobalt salt is dissolved in an inorganic acid in the redissolution step S5, and the redissolved liquid in which cobalt is redissolved is subjected to solvent extraction in the solvent extraction step S6 to separate copper contained in the redissolved liquid from the redissolved liquid.

The amount of the inorganic acid used in the redissolution solution may be sufficient to dissolve the cobalt salt recovered from the treatment target solution in the primary pH adjustment step S3 and less than the amount of the inorganic acid used in the treatment target solution for dissolving the metal such as cobalt. In particular, when the liquid to be treated is a liquid obtained by acid leaching of waste lithium ion batteries, the amount of the waste lithium ion batteries to be dissolved is large, and therefore, the amount of the inorganic acid used for acid leaching is also large, and the amount of the liquid to be treated is also large. Therefore, by once removing cobalt from the liquid to be treated and then dissolving cobalt again with the inorganic acid as in the cobalt recovery method of the present embodiment, the amount of the re-dissolved solution in which cobalt is dissolved can be significantly reduced as compared with the amount of the first liquid to be treated. When the amount of the re-dissolved solution is reduced, the amount of the extractant used for solvent extraction for separating impurity metals such as copper can be reduced, and therefore the cost of the extractant can be reduced. Further, since impurity metals such as copper are removed from the redissolved solution by solvent extraction, cobalt can be recovered with high purity. As described above, the cobalt recovery method according to the present embodiment can recover cobalt from a liquid to be treated with high purity at low cost.

In addition, according to the cobalt recovery method of the present embodiment, the extraction agent used in the solvent extraction step S6 is subjected to reverse extraction in the reverse extraction step S9, whereby the impurity metal such as copper is reversely extracted from the extraction agent from which the impurity metal such as copper is extracted. The extractant subjected to the back extraction is then supplied to the solvent extraction step S6 and reused, and therefore the amount of extractant used in the solvent extraction step S6 can be reduced.

In addition, according to the cobalt recovery method of the present embodiment, in the dissolving step S16, crystals of an inorganic salt (sodium sulfate in the present embodiment) contained in the precipitate separated from the treatment target liquid in the solid-liquid separation step S13 are dissolved to prepare an inorganic salt solution, and then bipolar membrane electrodialysis is performed in the electrodialysis step S17, thereby recovering an inorganic acid and an alkali from the inorganic salt solution. The recovered inorganic acid and alkali are then supplied to the acid leaching step S1, the primary pH adjustment step S3, the redissolution step S5, the secondary pH adjustment step S7, and the like, and reused, so that the amounts of the inorganic acid and alkali used in the respective steps can be reduced.

According to the cobalt recovery method of the present embodiment, the condensed water generated in the concentration step S11 is used for various treatments, and therefore, the condensed water can be effectively used. Further, the crystals obtained in the solid-liquid separation steps S4, S8, S13, and S15 are washed with condensed water, whereby the recovery rate of each crystal can be further improved.

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

As a modification, for example, in the embodiment of fig. 17 to 19, the following configuration may be adopted: the primary pH adjustment step S3 includes a first pH adjustment step S3-1 and a second pH adjustment step S3-3 as shown in FIGS. 21 and 22.

In the first pH adjustment step S3-1, the pH of the treatment target liquid is adjusted to 4 or more and 7 or less, preferably 4 or more and 6 or less, more preferably 4 or more and 5 or less by adding an alkali. Accordingly, in addition to copper in the treatment liquid, most of the impurity metals such as iron and aluminum are precipitated in the form of crystals of inorganic salts such as hydroxides, and removed from the treatment liquid. As the base used for pH adjustment, for example, sodium hydroxide, potassium hydroxide, lithium hydroxide, or the like can be used, and in the present embodiment, sodium hydroxide is used from the viewpoint of low cost and easy handling. In the first pH adjustment step S3-1, the method for adjusting the pH of the liquid to be treated is not particularly limited, and a commonly-used method can be used. Examples thereof include: a method of adding an aqueous alkali solution such as an aqueous sodium hydroxide solution while stirring the liquid to be treated in the first pH adjustment tank 2A. The first pH adjustment step S3-1 is preferably performed while raising the temperature of the liquid to be treated to a constant temperature, for example, in the range of 30 ℃ to 80 ℃.

The aqueous alkali solution added in the first pH adjustment step S3-1 is preferably diluted to an alkali concentration of less than 1.0mol/L. Thus, in the first pH adjustment step S3-1, cobalt in the liquid to be treated can be inhibited from precipitating as a cobalt salt together with an impurity metal such as copper and being removed from the liquid to be treated. However, if the alkali concentration is too low, it is preferable that the lower limit of the alkali concentration is 0.1mol/L or more because a large amount of an alkali aqueous solution is necessary for pH adjustment in the first pH adjustment step S3-1 and the amount of the liquid to be treated after pH adjustment increases. In order to effectively suppress the removal of cobalt in the treatment target liquid from the treatment target liquid in the first pH adjustment step S3-1, the alkali concentration of the aqueous alkaline solution added in the first pH adjustment step S3-1 is preferably 0.5mol/L or less, and more preferably 0.2mol/L or less.

In the first pH adjustment step S3-1, in order to reduce the amount of the aqueous alkali solution used for pH adjustment, the pH of the liquid to be treated may be adjusted to 4 or more and 7 or less by adding an aqueous alkali solution having a high 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 of less than 4 and, after the pH of the liquid to be treated reaches the predetermined value, adding an aqueous alkali solution having a dilute alkali concentration of less than 1.0mol/L to the liquid to be treated. The predetermined value of the pH of the liquid to be treated may be set in a range of 2 to 3.

The liquid to be treated after the first pH adjustment step S3-1 is supplied to a solid-liquid separation step S3-2. In the solid-liquid separation step S3-2, a precipitate of crystals of a salt containing an impurity metal such as copper precipitated in the solid-liquid separation step S3-2 is separated by a solid-liquid separator. The precipitate recovered in the solid-liquid separation step S3-2 is washed with a washing liquid. The washing waste liquid after washing is preferably supplied to the second pH adjustment step S3-3 after washing together with the liquid to be treated. Thus, lithium contained in the washing waste liquid can be supplied from the second pH adjustment step S3-3 to the carbonation step S14 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 S14. The water used for washing the precipitates is not particularly limited, and condensed water generated in the concentration step S11 is preferably used, whereby the condensed water can be effectively used.

In the second pH adjustment step S3-3, the pH of the treatment target liquid is adjusted to 7 or more, preferably 7 or more and 13 or less, more preferably 7 or more and 11 or less, and further preferably 8 or more and 10 or less by adding an alkali. Thus, cobalt in the treatment liquid precipitates in the form of a crystal of a cobalt salt such as cobalt hydroxide. In the second pH adjustment step S3-3, in addition to cobalt, valuable metals such as nickel and manganese, and impurity metals such as copper remaining in the treatment liquid may be precipitated in the form of crystals of inorganic salts such as hydroxides and removed from the treatment liquid. As the base used for pH adjustment, for example, sodium hydroxide, potassium hydroxide, lithium hydroxide, or the like can be used, and in the present embodiment, sodium hydroxide is used from the viewpoint of low cost and easy handling.

The method for adjusting the pH of the liquid to be treated in the second pH adjustment step S3-2 is not particularly limited, and a commonly performed method can be used. For example, a method of adding an aqueous alkali solution such as an aqueous sodium hydroxide solution while stirring the liquid to be treated in the second pH adjustment tank 2B may be mentioned. When the pH is adjusted, the temperature of the liquid to be treated is preferably raised to a constant temperature in the range of, for example, 30 ℃ to 80 ℃. The alkali concentration of the aqueous alkali solution added in the second pH adjustment step S3-3 is not particularly limited, but is preferably not less than the alkali concentration of the aqueous alkali solution used in the first pH adjustment step S3-1, and more preferably not less than 0.2 mol/L. The liquid to be treated after the second pH adjustment step S3-3 is supplied to the solid-liquid separation step S4.

According to the embodiment shown in fig. 21 and 22, most of the impurity metals such as copper, aluminum, and iron can be removed from the liquid to be treated in the first pH adjustment step S3-1, in which the impurity metals such as cobalt and copper are dissolved. Further, by adjusting the pH of the liquid to be treated with a dilute aqueous alkali solution having an alkali concentration of less than 1.0mol/L, the removal of impurity metals such as cobalt and copper from the liquid to be treated can be suppressed, as in the cobalt recovery method of the first embodiment, and therefore the amount of cobalt in the liquid to be treated supplied to the second pH adjustment step S3-3 can be maintained high. Therefore, in the subsequent secondary pH adjustment step S7 for recovering cobalt, cobalt can be recovered with high purity and high recovery rate.

Furthermore, according to the embodiment of fig. 21 and 22, since the diluted alkaline aqueous solution having an alkaline concentration of less than 1.0mol/L is used in the first pH adjustment step S3-1, the amount of the liquid to be treated supplied to the subsequent carbonation step S14 for lithium recovery increases, but the amount of the liquid to be treated can be reduced and the lithium concentration in the liquid to be treated can be increased by evaporating and concentrating the liquid to be treated in the concentration step S11 before the carbonation step S14. Therefore, the recovery rate of lithium carbonate can be improved favorably in the carbonation step S14.

The primary pH adjustment step S3 may include 3 or more steps depending on the components contained in the waste lithium ion battery.

As another modification example, in the embodiment of fig. 17 to 19, the impurity removal step S10 for removing at least calcium and/or magnesium is performed on the liquid to be treated before the concentration step S11, but instead of this step or in addition to this step, an impurity removal step for removing at least calcium and/or magnesium may be performed in the same manner on the inorganic salt solution before the electrodialysis step S17. The same modifications can be made to the embodiments of fig. 21 and 22.

As another modification, in the embodiment of fig. 17 to 19, a treatment step for removing impurities such as silicon contained in the inorganic salt solution may be performed after the dissolution step S16 and before the electrodialysis step S17. This treatment step may be performed in place of the impurity removal step S10 or in addition to the impurity removal step S10. As an example of the treatment step, an inorganic salt (sodium sulfate in the present embodiment) contained in an inorganic salt solution is recrystallized by evaporation, concentration, or the like, and then the crystals of the inorganic salt are separated into solid and liquid, and recovered in an aqueous solution containing the crystals of the inorganic salt. The recovered crystals of inorganic salt are then dissolved, for example with water, to regenerate the inorganic salt solution. The regenerated inorganic salt solution is supplied to the electrodialysis step S17.

In this embodiment, by removing silicon contained in the inorganic salt solution before the electrodialysis step S17, the amount of impurities in the inorganic solution subjected to electrodialysis in the electrodialysis step S17 is also reduced, and thus the performance of the bipolar membrane can be maintained high. Furthermore, when the dilute inorganic salt solution (desalted solution) after the electrodialysis step S17 is supplied to the evaporation and concentration apparatus 9 and evaporation and concentration are performed again in the concentration step S11, the amount of impurities in the desalted solution is reduced, and thereby the generation and adhesion of scale on the heat transfer surface of the heat exchanger of the evaporation and concentration apparatus 9 in the concentration step S11 can be suppressed. Further, since the amount of impurities in the liquid to be treated obtained in the solid-liquid separation step S15 after the carbonation step S14 is reduced, most of the liquid to be treated after the solid-liquid separation step S15 can be circulated again in the system. Therefore, lithium remaining in the liquid to be treated after the solid-liquid separation step S15 can be more sufficiently recovered, and therefore lithium can be recovered at a high recovery rate. It should be noted that similar modifications can be made to any of the above embodiments.

As another modification, in the embodiment of fig. 17 to 19, as shown in fig. 23 and 24, a baking step S0 for baking the spent lithium ion battery may be further included before the acid leaching step S1. The method for firing the spent lithium ion batteries in the firing step S0 is not particularly limited, and a known firing apparatus 14 may be used.

In the embodiment shown in fig. 23 and 24, the off-gas generated in the baking device 14 (baking step S0) is supplied to the carbonation step S14 (carbonation tank 11), and the off-gas is formed into carbon dioxide and mixed with the liquid to be treated in the carbonation step S14. This can reduce the amount of carbon dioxide used in the carbonation step S14. In addition, the temperature of the treatment target liquid may be raised in the carbonation step S14. It should be noted that the same changes can be made to any of the above embodiments.

As another modification, in the embodiment of fig. 17 to 19, the method of recovering lithium in the impurity removal step S10 and subsequent steps is not particularly limited, and various methods can be used. It should be noted that similar modifications can be made to any of the above embodiments.

As another modification, a case of recovering cobalt from the waste lithium ion battery is exemplified in the embodiments of fig. 17 to 19, but the present disclosure is not limited to a method for recovering cobalt from the waste lithium ion battery. It should be noted that similar modifications can be made to any of the above embodiments.

Description of the reference numerals

S0 (FIG. 15) baking step

S1 (FIG. 1, FIG. 9, FIG. 11, FIG. 13 and FIG. 15) acid leaching step

S3 (FIGS. 1, 9, 11, 13 and 15) one-time low pH adjustment step

S4 (FIGS. 1, 9, 11, 13 and 15) solid-liquid separation step (first impurity metal separation step)

S5 (FIGS. 1, 9, 11, 13, and 15) one high pH adjustment step

S6 (FIGS. 1, 9, 11, 13 and 15) solid-liquid separation step (Primary cobalt separation step)

S7-1 (FIG. 1, FIG. 9, FIG. 11, FIG. 13, and FIG. 15) redissolution step

S7-2 (FIG. 1, FIG. 11, FIG. 13 and FIG. 15) and S7-3 (FIG. 9) Secondary Low pH adjustment step

S7-2 (FIG. 9), S7-4 (FIG. 11), and S7-7 (FIG. 13) solvent extraction step

S7-3 (FIGS. 1, 11, 13 and 15) and S7-4 (FIG. 9) precipitation step (secondary impurity metal separation step)

S7-4 (FIGS. 1, 13 and 15) and S7-5 (FIGS. 9 and 11) two high pH adjustment steps

S7-5 (FIGS. 1, 13 and 15) and S7-6 (FIGS. 9 and 11) solid-liquid separation step (Secondary cobalt separation step)

S7-7 (FIGS. 9 and 11) and S7-10 reverse extraction step

S7-8 (FIG. 13) three high pH adjustment steps

S7-9 (FIG. 13) solid-liquid separation step (third cobalt separation step)

S8-2 (FIG. 2) concentration step

S8-5 (FIG. 2) carbonation Process

S8-6 (FIG. 2) solid-liquid separation step (lithium separation step)

Claims

1. A cobalt recovery method comprising the steps of:

a primary low pH adjustment step of adding an alkali to an acidic treatment target solution in which at least cobalt and impurity metals are dissolved to adjust the pH to 4 or more and 7 or less;

a primary impurity metal separation step of separating a precipitate containing crystals of a salt of an impurity metal precipitated in the primary low pH adjustment step from a liquid to be treated by using a solid-liquid separator;

a primary high pH adjustment step of adding an alkali to the liquid to be treated after the primary impurity metal separation step to adjust the pH to 7 or more;

a primary cobalt separation step of separating a precipitate containing crystals of a cobalt salt precipitated in the primary high pH adjustment step from a liquid to be treated by using a solid-liquid separation apparatus;

a re-dissolving step of adding an inorganic acid to dissolve the precipitate separated in the primary cobalt separation step, thereby producing a re-dissolved solution;

a secondary low pH adjustment step of adjusting the pH to 4 or more and 7 or less by adding an alkali to the redissolved solution;

a secondary impurity metal separation step of precipitating a precipitate containing crystals of the impurity metal salt precipitated in the secondary low pH adjustment step by its own weight or centrifugal separation, and separating the precipitate into a supernatant liquid and a slurry containing the precipitate;

a secondary high pH adjustment step of adjusting the pH to 7 or more by adding an alkali to a resolvent as a supernatant after the secondary impurity metal separation step; and the number of the first and second groups,

and a secondary cobalt separation step of recovering, from the redissolved solution, a precipitate containing crystals of a cobalt salt precipitated in the secondary high pH adjustment step, using a solid-liquid separation apparatus.

2. The cobalt recovery method according to claim 1, wherein the slurry containing the precipitate separated in the secondary impurity metal separation step is supplied to at least one of the liquid to be treated before the primary low pH adjustment step, the liquid to be treated in the primary low pH adjustment step, and the liquid to be treated before the primary impurity metal separation step.

3. The cobalt recovery method according to claim 1 or 2, further comprising a solvent extraction step of performing solvent extraction using an extractant on the redissolved solution generated in the redissolution step to separate impurity metals from the redissolved solution,

in the secondary low pH adjustment step, an alkali is added to the redissolved solution after the solvent extraction step to adjust the pH to 4 or more and 7 or less.

4. The cobalt recovery method according to claim 1 or 2, further comprising a solvent extraction step of performing solvent extraction using an extractant on the redissolved solution as a supernatant after the secondary impurity metal separation step, thereby separating impurity metals from the redissolved solution,

in the secondary high pH adjustment step, an alkali is added to the redissolved solution after the solvent extraction step to adjust the pH to 7 or more.

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

a re-dissolution step of adding an inorganic acid to dissolve the precipitate separated in the secondary cobalt separation step, thereby producing a re-dissolved solution;

a solvent extraction step of subjecting the redissolved solution to solvent extraction using an extractant to separate impurity metals from the redissolved solution;

a third high pH adjustment step of adjusting the pH to 7 or more by adding an alkali to the redissolved solution after the solvent extraction step; and (c) a second step of,

a third cobalt separation step of separating a precipitate containing crystals of a cobalt salt precipitated in the third high pH adjustment step from the redissolved solution.

6. The cobalt recovery method according to any one of claims 1 to 4, further comprising an acid leaching step of leaching the spent lithium ion battery with an inorganic acid to dissolve cobalt and impurity metals, thereby obtaining the liquid to be treated.

7. The cobalt recovery method according to any one of claims 1 to 5, wherein lithium is dissolved in the liquid to be treated,

the cobalt recovery method further comprises the following steps:

a concentration step of evaporating and concentrating the treated liquid after the primary cobalt separation step;

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 (c) a second step of,

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

8. The cobalt recovery method according to claim 7, wherein the re-dissolved solution after the secondary cobalt separation step is concentrated by evaporation in the concentration step.