JP2021017627A - Lithium recovery method - Google Patents

Abstract

To provide a lithium recovery method capable of recovering lithium with high purity from a liquid to be treated in which lithium and an inorganic salt are dissolved.SOLUTION: The lithium recovery method includes: a concentration step S8 of evaporating and concentrating, under low pressure lower than atmospheric pressure, a liquid to be treated in which lithium and an inorganic salt are at least dissolved; a carbonation step S10 of mixing carbon dioxide gas into the liquid to be treated and/or adding a water-soluble carbonate to the liquid to be treated after the concentration step S8; and a solid-liquid separation step S11 of separating, from the liquid to be treated, a precipitate containing crystals of lithium carbonate having been precipitated by the carbonation step S10. In the carbonation step S10, the temperature of the liquid to be treated is set to be equal to or higher than the evaporation temperature of the liquid to be treated in the concentration step S8.SELECTED DRAWING: Figure 1

Description

The present invention relates to a lithium recovery method for recovering lithium from a liquid to be treated in which at least lithium is dissolved, and in particular, a lithium recovery method used for recovering lithium from a waste lithium ion battery.

Lithium-ion batteries are attracting attention as lightweight and high-energy density batteries, and are widely used as batteries for various portable devices, electric vehicles, electrically power assisted bicycles, and the like. Lithium transition metal oxides such as lithium cobalt oxide and lithium nickel nickel oxide are used as the positive electrode active material in the positive electrode of this lithium ion battery, and it is not possible to recover valuable metals cobalt and nickel from waste lithium ion batteries. Many methods have been proposed because they are extremely important from the perspective of effective use of resources.

On the other hand, many methods for recovering lithium from waste lithium-ion batteries have not been proposed because the unit price of lithium is low. However, the demand for lithium-ion batteries is increasing more and more, and the amount of waste is expected to increase in the future, so it would be beneficial if lithium could be recovered efficiently.

In Patent Document 1, a used lithium metal gel and a solid polymer electrolyte secondary battery are dissolved in sulfuric acid, and lithium hydroxide or ammonium hydroxide is added to a lithium sulfate-containing liquid containing lithium sulfate obtained thereby. By neutralizing, the salt of the impurity metal (aluminum hydroxide) is precipitated as crystals and separated, and the lithium sulfate-containing liquid is evaporated and concentrated, and then carbonized, thereby containing lithium contained in the lithium sulfate-containing liquid. Is described as a method of precipitating lithium carbonate crystals to separate and recover the mixture.

Japanese Patent Publication No. 2004-508964

However, in the method described in Patent Document 1, when ammonium hydroxide is used for neutralization when removing impurities (aluminum hydroxide) from the lithium sulfate-containing liquid, the inorganic salt ammonium sulfate sulfate is added to the neutralized lithium sulfate-containing liquid. Is included. If carbonation is performed in a state where the lithium sulfate-containing liquid contains an inorganic salt, crystallization may occur because the concentration of the inorganic salt in the lithium sulfate-containing liquid increases due to the concentration. Therefore, since the lithium carbonate contains an inorganic salt during carbonation, there is room for improvement in that the purity of the recovered lithium carbonate is lowered.

The present invention has been made to solve the above problems, and is to provide a lithium recovery method capable of recovering lithium with high purity from a liquid to be treated in which lithium and an inorganic salt are dissolved.

The lithium recovery method of the present invention comprises a concentration step of heating a liquid to be treated in which at least lithium and an inorganic salt are dissolved at a low pressure lower than atmospheric pressure to evaporate and concentrate, and carbonic acid in the liquid to be treated after the concentration step. Includes a carbonation step of mixing gas and / or adding a water-soluble carbonate, and a solid-liquid separation step of separating a precipitate containing lithium carbonate crystals precipitated by the carbonation step from the liquid to be treated. The carbonation step is characterized in that the temperature of the liquid to be treated is equal to or higher than the evaporation temperature of the liquid to be treated in the concentration step.

In the lithium recovery method of the present invention, it is preferable to evaporate and concentrate the liquid to be treated under a pressure of 10 kPa or more and 70 kPa or less in the concentration step.

Further, in the lithium recovery method of the present invention, it is preferable that at least a part of the liquid to be treated after the solid-liquid separation step is evaporated and concentrated in the concentration step.

Further, in the lithium recovery method of the present invention, in the concentration step, the inorganic salt contained in the solution to be treated is precipitated as crystals, and the precipitate separated from the solution to be treated after the concentration step contains the inorganic salts as crystals. A dissolution step of dissolving a salt to produce an inorganic salt solution and a bipolar membrane electrodialysis of the inorganic salt solution obtained by the dissolution step are performed to separate and recover the inorganic acid together with the alkali from the inorganic salt solution. It is preferable to further include an electrodialysis step.

Further, in the lithium recovery method of the present invention, before the concentration step, an acid elution step of leaching a waste lithium ion battery with an inorganic acid to elute lithium and an alkali in the lithium-containing liquid obtained by the acid elution step. It is preferable that the liquid to be treated is produced by further including a pH adjusting step of adding and adjusting the pH, and separating the precipitate precipitated by the pH adjusting step from the lithium-containing liquid.

Further, in the lithium recovery method of the present invention, it is preferable to reuse at least a part of the liquid to be treated after the solid-liquid separation step as an alkali to be added in the pH adjustment step.

Further, in the lithium recovery method of the present invention, the alkali recovered in the electrodialysis step is reused as an alkali to be added in the pH adjustment step, and the inorganic acid recovered in the electrodialysis step is used in the acid elution step. It is preferable to reuse it as an acid.

According to the lithium recovery method of the present invention, the liquid to be treated is evaporated and concentrated in the concentration step before the carbonation step to reduce the amount of the liquid to be treated and increase the concentration of lithium in the liquid to be treated. Therefore, the recovery rate of lithium carbonate can be satisfactorily improved in the carbonation step.

Further, in the concentration step, by evaporating and concentrating the liquid to be treated under low pressure, the temperature of the liquid to be treated after evaporative concentration can be lowered as compared with the case where the liquid to be treated is evaporated and concentrated under atmospheric pressure. Therefore, it is possible to secure a large room for raising the temperature of the liquid to be treated in the subsequent carbonation step, and the evaporation temperature of the liquid to be treated (the boiling point of water contained in the liquid to be treated) is lowered under low pressure. Energy saving can be achieved by keeping the energy required for evaporation and concentration low. When the temperature of the liquid to be treated is low in the carbonation step, the inorganic salt contained in the liquid to be treated crystallizes, so that the temperature of the liquid to be treated during carbonation is higher than the evaporation temperature of the liquid to be treated in the concentration step. By increasing the solubility of the inorganic salt remaining in the liquid to be treated, the crystallization of the inorganic salt can be suppressed during carbonation. Further, if the temperature of the liquid to be treated is high during carbonation, the solubility of lithium carbonate decreases, and the amount of lithium carbonate crystals recovered can be increased. Therefore, it is possible to obtain high-purity lithium carbonate with high efficiency.

It is a flowchart which shows roughly the procedure of the lithium recovery method of one Embodiment of this invention. It is a schematic diagram which shows the schematic structure of the processing apparatus used for the lithium recovery method of FIG. It is a schematic diagram which shows the schematic structure of the bipolar membrane electrodialysis apparatus. It is a flowchart which shows generally the procedure of the lithium recovery method of another embodiment of this invention. It is a schematic diagram which shows the schematic structure of the processing apparatus used for the lithium recovery method of FIG. It is a flowchart which shows generally the procedure of the lithium recovery method of another embodiment of this invention. It is a schematic diagram which shows the schematic structure of the processing apparatus used for the lithium recovery method of FIG.

Hereinafter, the actual form of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows a procedure of each step of the lithium recovery method of the present embodiment, and FIG. 2 shows a schematic configuration of a processing device 10 that implements the lithium recovery method. In the lithium recovery method of the present embodiment, in addition to lithium, a liquid to be treated containing a strong acid such as hydrochloric acid, sulfuric acid, hydrofluoric acid and phosphoric acid and an inorganic salt of an alkali metal such as potassium and sodium or an alkaline earth metal is used. It can be suitably used for processing, and the case of recovering lithium from a waste lithium ion battery will be described below as an example.

The lithium recovery method of this embodiment is
-The acid elution step S1 in which the waste lithium ion battery is leached with an inorganic acid to elute lithium,
-A solid-liquid separation step S2 for separating an insoluble residue from the lithium-containing liquid obtained in the acid elution step S1 and
-The pH adjusting steps S3 and S5 for adjusting the pH by adding an alkali to the lithium-containing liquid after the solid-liquid separation step S2.
-The solid-liquid separation steps S4 and S6 for separating the precipitate from the lithium-containing liquid after the pH adjustment steps S3 and S5,
-The impurity removing step S7 in which the liquid to be treated from which the precipitate is separated from the lithium-containing liquid after the pH adjusting steps S3 and S5 is chelated.
-The concentration step S8 for evaporating and concentrating the liquid to be treated in which at least lithium and the inorganic salt are dissolved after the impurity removal step S7,
-A solid-liquid separation step S9 for separating a precipitate containing inorganic salt crystals from the liquid to be treated after the concentration step S8.
-In the carbonation step S10 in which carbon dioxide gas is mixed with the liquid to be treated after the solid-liquid separation step S9 and / or a water-soluble carbonate is added.
-A solid-liquid separation step S11 for separating the precipitate containing lithium carbonate crystals precipitated in the carbonation step S10 from the liquid to be treated.
including. The lithium recovery method of the present embodiment further
-The dissolution step S12, which dissolves the crystals of the inorganic salt contained in the precipitate separated from the liquid to be treated in the solid-liquid separation step S9 to generate an inorganic salt solution,
-The electrodialysis step S13 in which the alkali and the inorganic acid are separated and recovered from the inorganic salt solution by performing bipolar membrane electrodialysis on the inorganic salt solution after the dissolution step S12.
Have.

Waste lithium-ion batteries for which lithium is to be recovered include used lithium-ion batteries whose charge capacity has decreased due to the use of a predetermined number of charge / discharge cycles, as well as semi-finished products and product specifications that occur due to defects in the battery manufacturing process. Includes old model inventory reorganized products that occur due to changes. The waste lithium ion battery may be pulverized or roasted, or may be a powder obtained by pulverizing and roasting.

First, in the acid elution step S1, the above-mentioned waste lithium ion battery is leached with an inorganic acid to elute lithium and other metals such as aluminum, nickel, cobalt, and iron. As the inorganic acid, for example, sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid and the like can be used, but in this embodiment, hydrochloric acid is used.

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

In the next solid-liquid separation step S2, the insoluble residue is separated from the lithium-containing liquid by filtering the lithium-containing liquid obtained in the acid elution step S1. The insoluble residue is mainly a carbon material, a metal material, and an organic material that are insoluble in inorganic acids. As a method for solid-liquid separation, for example, various filtration devices such as pressure filtration (filter press), vacuum filtration, and centrifugal filtration, and known devices such as a centrifuge such as a decanter type can be used. The same applies to the following solid-liquid separation steps S4, S6, S9, and S11.

In the next pH adjusting steps S3 and S5, an alkali is added to the lithium-containing liquid (filter solution) after the solid-liquid separation step S2, and the pH is adjusted to a predetermined range to adjust the pH of the above-mentioned metal in the lithium-containing liquid. Of these, metals other than lithium are removed from the lithium-containing liquid. As the alkali, for example, sodium hydroxide, potassium hydroxide, lithium hydroxide and the like can be used, but in this embodiment, sodium hydroxide is used because of its low cost and ease of handling.

In the pH adjusting steps S3 and S5, the method for adjusting the pH of the lithium-containing liquid is not particularly limited, and a commonly used method can be used. For example, by adding an alkaline aqueous solution such as a sodium hydroxide aqueous solution while stirring the lithium-containing liquid in the first pH adjusting tank 2 and the second pH adjusting tank 3, metals other than lithium in the lithium-containing liquid are hydroxylated. Precipitate and precipitate as crystals of inorganic salts such as substances. In the present embodiment, the pH adjusting steps S3 and S5 are divided into a first pH adjusting step S3 and a second pH adjusting step S5.

In the first pH adjusting step S3, the pH of the lithium-containing liquid is adjusted to 4 to 7, preferably 4 to 6 by adding an alkali. As a result, impurity metals (for example, aluminum and iron) in the lithium-containing liquid are precipitated and precipitated as crystals of inorganic salts such as hydroxides (for example, aluminum hydroxide and iron hydroxide). In the first pH adjusting step S3, it is preferable to carry out the lithium-containing liquid while heating it to a constant temperature, for example, at 30 ° C. to 60 ° C.

The alkaline aqueous solution added in the first pH adjusting step S3 is preferably diluted with an alkali concentration of less than 1.0 mol / L. As a result, it is possible to prevent cobalt in the liquid to be treated from being precipitated and precipitated as cobalt salt crystals together with the impurity metal in the first pH adjusting step S3 and being removed from the liquid to be treated. However, if the alkali concentration is excessively low, it is necessary to use a large amount of an alkaline aqueous solution for pH adjustment in the first pH adjustment step S3, and the amount of the liquid to be treated after pH adjustment is also large. The lower limit of the alkali concentration is preferably 0.1 mol / L or more. Further, in order to effectively suppress the removal of cobalt in the liquid to be treated from the liquid to be treated in the first pH adjustment step S3, the alkali concentration of the alkaline aqueous solution added in the first pH adjustment step S3 is set. It is preferably 0.5 mol / L or less, and more preferably 0.2 mol / L or less.

In the first pH adjustment step S3, in order to reduce the amount of the alkaline aqueous solution used for pH adjustment, a strong alkali concentration of 1.0 mol / L or more is obtained until the pH of the liquid to be treated becomes a predetermined value smaller than 4. After the pH of the liquid to be treated reaches a predetermined value, an aqueous alkali solution having a low alkali concentration of less than 1.0 mol / L is added to the liquid to be treated. Therefore, the pH of the liquid to be treated can be adjusted to 4 to 7. The predetermined value of the pH of the liquid to be treated can be set within the range of 2 to 3.

The precipitate precipitated and precipitated in the first pH step S3 is separated from the lithium-containing liquid by filtering the lithium-containing liquid in the next solid-liquid separation step S4. The impurity metal removed from the lithium-containing liquid in the first pH adjusting step S3 may also contain copper or the like. In the solid-liquid separation step S4, it is preferable that the precipitate is washed with a washing liquid, and the washing waste liquid after washing is circulated together with the liquid to be treated (filter liquid) in the next second pH adjustment step S5. As a result, the lithium contained in the cleaning waste liquid can be supplied to the second pH adjustment step S5 together with the lithium contained in the filtrate. The water used for washing the precipitate is not particularly limited, but it is preferable to use the condensed water generated when the liquid to be treated is evaporated and concentrated in the concentration step S8 described later, whereby the condensed water is used. Can be effectively used.

In the second pH adjusting step S5, an alkali is added to the lithium-containing liquid (filter solution) after the solid-liquid separation step S4 to adjust the pH to the range of 7 to 11, preferably 8 to 10. As a result, valuable metals (for example, cobalt and nickel) in the lithium-containing liquid are precipitated and precipitated as crystals of inorganic salts such as hydroxides (for example, cobalt hydroxide and nickel hydroxide). The alkali concentration of the alkaline aqueous solution added in the second pH adjusting step S5 is not particularly limited, but is preferably equal to or higher than the alkaline concentration of the alkaline aqueous solution used in the first pH adjusting step S3.

The precipitate precipitated and precipitated in the second pH step S5 is separated from the lithium-containing liquid by filtering the lithium-containing liquid in the next solid-liquid separation step S6. In addition, manganese and the like may be contained in the valuable metal removed from the lithium-containing liquid in the second pH adjusting step S5.

On the other hand, in the lithium-containing liquid (filter solution) after the solid-liquid separation step S6, in addition to lithium, the inorganic acid (hydrochloric acid in this embodiment) and alkali (hydrochloric acid in this embodiment) added in the acid elution step S1 and the pH adjusting steps S3 and S5. In this embodiment, the inorganic salt (sodium chloride (NaCl) in this embodiment) is dissolved by (sodium hydroxide). In the present embodiment, the lithium-containing liquid after the pH adjustment steps S3 and S5 corresponds to the "liquid to be treated" described in the claims. At least one of calcium, magnesium and silica may be further dissolved in the liquid to be treated.

In the solid-liquid separation step S6, it is preferable that the precipitate is washed with a washing liquid, and the washing waste liquid after washing is circulated to the next step together with the liquid to be treated (filter liquid). As a result, the lithium contained in the cleaning waste liquid can be supplied to the next step together with the lithium contained in the filtrate, and by carbonating in the carbonation step S10 described later, lithium can be recovered with a high recovery rate. .. The water used for washing the precipitate is not particularly limited, but it is preferable to use the condensed water generated when the liquid to be treated is evaporated and concentrated in the concentration step S8 described later, whereby the condensed water is used. Can be effectively used.

In the next impurity removing step S7, at least polyvalent cations such as calcium and / or magnesium contained in the liquid to be treated after the solid-liquid separation step S6 are removed. By removing calcium, magnesium, etc. contained as impurities in the liquid to be treated, it is possible to prevent scale from being generated and adhering to the heat transfer surface of the heat exchanger of the evaporation concentrator 5 in the concentration step S8 described later. It is possible to maintain high heat exchange efficiency. When the liquid to be treated contains calcium, magnesium, etc., the polyvalent cations such as calcium and magnesium contained in the inorganic solution are the cations of the bipolar membrane electrodialysis apparatus 9 in the electrodialysis step S13 described later. It may precipitate in the exchange membrane and cause deterioration of film performance. Therefore, it is necessary to prevent adverse effects on the cation exchange membrane of the bipolar membrane electrodialysis apparatus 9 by removing substances such as calcium and magnesium that hinder scaling in operating electrodialysis from the liquid to be treated in advance. And the performance of electrodialysis can be maintained high.

In the impurity removing step S7, the method for removing calcium and magnesium from the liquid to be treated is not particularly limited, and for example, a multivalent cation removing device 4 can be used. The polyvalent cation removing device 4 is a device that removes divalent or higher valent cations such as calcium ions and magnesium ions. For example, an ion exchange resin is provided inside and the liquid to be treated is used as an ion exchange resin. An example of a structure capable of adsorbing calcium ions and magnesium ions in contact with each other can be exemplified. As the polyvalent cation removing device 4, another example of a device in which a liquid to be treated can be passed through a column filled with a chelate resin can be exemplified. As the chelate resin, one capable of selectively capturing calcium ions and magnesium ions can be used, and examples thereof include iminodiacetic acid type and aminophosphate type. Further, examples of the multivalent cation removing device 4 include those to which a chelating agent is added. The impurities removed from the liquid to be treated in the impurity removing step S7 may contain silica (silicate ion) in addition to calcium and magnesium.

In the next concentration step S8, the liquid to be treated is concentrated by heating after the impurity removal step S7, that is, the liquid to be treated is concentrated by evaporating the water content in the liquid to be treated. As a result, the amount of the liquid to be treated decreases, and the lithium concentration in the liquid to be treated increases. Therefore, the recovery rate of lithium carbonate can be improved in the carbonation step S10 described later.

In the concentration step S8, it is preferable to evaporate and concentrate the liquid to be treated to a concentration at which lithium does not precipitate as crystals of a lithium salt such as lithium chloride in the liquid to be treated after concentration. As a result, the concentration of lithium in the liquid to be treated after concentration can be increased, and the recovery rate of lithium carbonate can be improved in the carbonation step S10 described later.

In this concentration step S8, the concentration of the inorganic salt in the liquid to be treated increases due to the evaporation and concentration of the liquid to be treated, so that the inorganic salt may crystallize. The inorganic salt contained in the liquid to be treated may or may not be precipitated as crystals in the concentration step S8. In the present embodiment, the inorganic salt contained in the liquid to be treated is precipitated as crystals in the concentration step S8, and the precipitate is separated from the liquid to be treated in the next solid-liquid separation step S9.

In the concentration step S8, the method for evaporating and concentrating the liquid to be treated is not particularly limited, and for example, an evaporation concentrator 5 can be used. The evaporative concentrator 5 is not particularly limited as long as the liquid to be treated can be concentrated by evaporation, and for example, a known evaporative concentrator such as a heat pump type, an ejector drive type, a steam type, or a flash type can be used. A heat pump type evaporation concentrator is preferable. When a heat pump type evaporation concentrator is used, the energy used can be significantly suppressed.

The inside of the evaporation concentrator 5 is maintained at a low pressure by connecting a vacuum pump (not shown), and in the concentration step S8, the liquid to be treated is heated under a low pressure lower than the atmospheric pressure to evaporate and concentrate. doing. When the liquid to be treated is evaporated and concentrated, the temperature of the liquid to be treated rises, but at low pressure, the evaporation temperature of the liquid to be treated (the boiling point of water contained in the liquid to be treated) is lower than that under atmospheric pressure, so that the liquid to be treated evaporates under low pressure. By concentrating, the temperature of the liquid to be treated after evaporative concentration is lowered by that amount. Therefore, it is possible to secure a large room for raising the temperature of the liquid to be treated in the carbonation step S10 described later. In addition, since the evaporation temperature of the liquid to be treated is lowered under low pressure, the energy required for evaporation and concentration of the liquid to be treated can be suppressed to a low level to save energy.

The pressure inside the evaporation concentrator 5, that is, the atmospheric pressure when evaporating and concentrating the liquid to be treated is not particularly limited, but is preferably 10 kPa or more and 70 kPa or less, and is 15 kPa or more and 50 kPa or less. Is more preferable. The evaporation temperature of the liquid to be treated is preferably 45 ° C. or higher and 95 ° C. or lower, and more preferably 55 ° C. or higher and 80 ° C. or lower in relation to the above pressure (saturated water vapor pressure curve).

When the pressure is 10 kPa or more, the temperature of the liquid to be treated after evaporation and concentration can be set to a suitable low temperature so as not to be excessively lowered. Therefore, when raising the temperature of the liquid to be treated in the carbonation step S10 described later. The energy required for the process can be kept low. Further, since it is not necessary for the evaporation concentrator 5 to have a very high withstand voltage performance, the manufacturing cost of the apparatus can be kept low. On the other hand, when the pressure is 70 kPa or less, the temperature of the liquid to be treated after evaporation and concentration can be set to a suitable low temperature so as not to rise excessively. Therefore, the temperature of the liquid to be treated in the carbonation step S10 described later There is ample room to raise it. In addition, the energy required for evaporation and concentration of the liquid to be treated does not become too large, and energy saving can be effectively achieved.

Although not shown, a temperature sensor is provided at the bottom of the evaporation concentrator 5 or in the supply path of the liquid to be treated between the evaporation concentration device 5 and the carbonization tank 7 described later. The evaporation temperature of the liquid to be treated (the temperature of the liquid to be treated after evaporation concentration) is monitored by a temperature sensor. Further, although not shown, a pressure sensor is provided in the space above the evaporative concentrator 5, and the pressure inside the evaporative concentrator 5 (atmospheric pressure when evaporating and concentrating the liquid to be treated) is a pressure sensor. Is being monitored by.

In the next solid-liquid separation step S9, the precipitate containing crystals of an inorganic salt (sodium chloride in this embodiment) is separated from the liquid to be treated by filtering the liquid to be treated after the concentration step S8.

In the next carbonation step S10, the liquid to be treated is mixed with carbon dioxide gas and / or by adding a water-soluble carbonate to the liquid to be treated after the precipitate containing the crystals of the inorganic salt described above has been separated. The lithium inside is precipitated and precipitated as crystals of lithium carbonate. As a result, lithium in the liquid to be treated can be recovered as lithium carbonate. As the carbonate, for example, sodium carbonate, ammonium carbonate, potassium carbonate and the like can be used.

In this carbonation step S10, it is preferable to precipitate and precipitate lithium carbonate crystals by mixing carbon dioxide gas with the liquid to be treated. As described above, in the carbonation step S10, by using a material that does not contain an alkali metal such as sodium, it is possible to suppress the mixing of alkali metals other than lithium into the precipitated lithium carbonate crystals. Therefore, highly pure lithium carbonate can be recovered.

However, if the mixing of carbon dioxide gas is continued, the pH of the liquid to be treated drops, so that the amount of lithium carbonate precipitated may decrease. Therefore, it is preferable to stop the mixing of carbon dioxide gas before the pH of the liquid to be treated becomes 7 or less. Further, the pH may not be lowered by adding an alkali to the liquid to be treated. In that case, it is preferable to maintain the pH at 9 or higher by adding alkali. As the alkali to be added, sodium hydroxide, potassium hydroxide, lithium hydroxide and the like can be used.

In the carbonation step S10, the method of mixing carbon dioxide gas with the liquid to be treated is not particularly limited, and a commonly used method can be used. For example, by supplying carbon dioxide gas into the liquid to be treated in the form of fine bubbles by a nozzle while stirring the liquid to be treated in the carbonation tank 7, the carbon dioxide gas can be uniformly mixed with the liquid to be treated. , Lithium in the liquid to be treated and carbon dioxide gas can be efficiently reacted. Further, the liquid to be treated may be reacted with carbon dioxide gas by spraying it in an atmosphere of carbon dioxide gas.

In the carbonation step S10, the temperature of the liquid to be treated is set to be equal to or higher than the evaporation temperature of the liquid to be treated in the concentration step S8. If the temperature of the liquid to be treated is low during carbonation, the inorganic salt (sodium chloride in this embodiment) contained in the liquid to be treated may crystallize. Therefore, in the carbonation step S10, the liquid to be treated is heated to raise the temperature of the liquid to be treated at the time of carbonation higher than the evaporation temperature of the liquid to be treated, so that the inorganic material remaining in the liquid to be treated during carbonation is formed. The solubility of the salt is increased, and the crystallization of the inorganic salt can be suppressed. Therefore, when the lithium carbonate is recovered in the carbonation step S10, the purity of the lithium carbonate can be increased.

The temperature of the liquid to be treated at the time of carbonation is not particularly limited as long as it is equal to or higher than the evaporation temperature of the liquid to be treated, but is preferably higher than the evaporation temperature of the liquid to be treated and preferably less than 100 ° C. The method of heating the liquid to be treated in the carbonation step S10 is not particularly limited, and for example, a method of heating the liquid to be treated in the carbonation tank 7 by using a known heating means such as a heater is used. Can be done. Before supplying the liquid to be treated to the carbonation tank 7, the liquid to be treated may be preheated by using a preheating means such as a heat exchanger.

Further, the solubility of lithium carbonate decreases as the temperature of the liquid to be treated increases. Therefore, as the temperature of the liquid to be treated rises in the carbonation step S10, the solubility of lithium carbonate generated by the reaction of lithium in the liquid to be treated with carbon dioxide gas decreases. Therefore, the amount of lithium carbonate crystals precipitated can be increased.

As described above, the amount of lithium carbonate crystals recovered can be increased and the amount of inorganic salt crystals precipitated can be suppressed, so that high-purity lithium carbonate can be obtained with high efficiency.

In the next solid-liquid separation step S11, the precipitate containing lithium carbonate crystals is separated from the lithium-containing liquid by filtering the liquid to be treated after the carbonation step S10. In the solid-liquid separation step S11, impurities can be removed and the purity of lithium carbonate can be increased by washing the precipitate separated from the lithium-containing liquid with water or the like. The water used for washing the precipitate is not particularly limited, but it is preferable to use the condensed water generated when the liquid to be treated is evaporated and concentrated in the concentration step S8, whereby the condensed water is effective. It is available.

The liquid to be treated (filter liquid) after the solid-liquid separation step S11 is not particularly limited, but since it contains impurities, a part of it is discharged as a blow liquid, but a part of it is discharged into the system again. It is preferable to circulate. As a result, the lithium remaining in the liquid to be treated can be recovered, so that lithium can be recovered at a high recovery rate. It is preferable that the cleaning waste liquid after cleaning the above-mentioned precipitate containing lithium carbonate crystals is also circulated in the system again together with the liquid to be treated after the solid-liquid separation step S11.

When the liquid to be treated after the solid-liquid separation step S11 is circulated in the system again, it may be supplied to the evaporation concentrator 5 and evaporated and concentrated in the concentration step S8, but preferably, the first pH adjusting tank 2 and / Or supply to the second pH adjusting tank 3. Since the liquid to be treated after the solid-liquid separation step S11 is alkaline, it can be used as an alkali to be added in the pH adjusting steps S3 and S5. Furthermore, if the liquid to be treated after the solid-liquid separation step S11 contains a large amount of carbonate ions (CO ₃ ² −), the heat transfer of the heat exchanger of the evaporation concentrator 5 when evaporative concentration is performed in the concentration step S8. Carbonate crystals are deposited on the surface. Therefore, since the filtrate after the solid-liquid separation steps S2 and S4 is acidic, the filtrate to be treated after the solid-liquid separation step S11 is neutralized with the filtrate and carbonate ions are used as carbon dioxide gas from the filtrate. By removing the carbon dioxide, it is possible to prevent carbon dioxide crystals from depositing on the heat transfer surface of the heat exchanger of the evaporation concentrator 5 in the concentration step S8.

On the other hand, the crystals of the inorganic salt (sodium chloride in this embodiment) contained in the precipitate generated in the concentration step S8 (evaporation concentration device 5) and separated from the liquid to be treated in the solid-liquid separation step S9 are in the dissolution step. It is supplied to S12 (dissolving tank 8). In the dissolution step S12, the crystals of the inorganic salt are dissolved in the dissolution tank 8 with water, for example, so as to have a desired concentration to produce an inorganic salt solution. The temperature at this time is not particularly limited as long as it can dissolve the crystals of the inorganic salt. The water used for dissolving the inorganic salt is not particularly limited, but it is preferable to use the condensed water generated when the liquid to be treated is evaporated and concentrated in the concentration step S8, whereby the condensed water is used. Effective use is possible. The generated inorganic salt solution is supplied to the bipolar membrane electrodialysis apparatus 9.

In the next electrodialysis step S13, the bipolar membrane electrodialysis apparatus 9 separates and recovers the alkali and the inorganic acid from the inorganic salt solution after the dissolution step S12. As the bipolar membrane electrodialysis apparatus 9, for example, as shown in FIG. 3, a cell 90 having an anion exchange membrane 91, a cation exchange membrane 92, and two bipolar membranes 93 and 94 between the anode 95 and the cathode 96. A three-chamber cell type bipolar membrane electrodialysis apparatus in which a plurality of the two are laminated can be preferably used. In the bipolar membrane electrodialysis apparatus 9 of the present embodiment, the desalting chamber R1 is formed by the anion exchange membrane 91 and the cation exchange membrane 92, and the acid chamber R2 is formed between the anion exchange membrane 91 and one of the bipolar membranes 93. An alkali chamber R3 is formed between the cation exchange membrane 92 and the other bipolar membrane 94. An anode chamber R4 and a cathode chamber R5 are formed on the outside of each of the bipolar films 93 and 94, and an anode 95 is arranged in the anode chamber R4 and a cathode 96 is arranged in the cathode chamber R5, respectively.

In this electrodialysis step S13, an inorganic salt solution is introduced into the desalting chamber R1, and pure water is introduced into the acid chamber R2 and the alkaline chamber R3, respectively. As a result, when the inorganic salt solution contains, for example, sodium chloride, in the desalting chamber R1, sodium ions (Na ⁺ ) pass through the cation exchange membrane 92 and chloride ions (Cl ⁻ ) are negative. It passes through the ion exchange membrane 91. On the other hand, in the acid chamber R2 and the alkali chamber R3, the supplied pure water is dissociated into hydrogen ions (H ⁺ ) and hydroxide ions (OH ⁻ ) in the bipolar films 93 and 94, and in the acid chamber R2, hydrogen ions ( H ⁺ ) binds to chloride ion (Cl ⁻ ) to generate hydrochloric acid (HCl), and in the alkali chamber R3, hydroxide ion (OH ⁻ ) binds to sodium ion (Na ⁺ ) to form sodium hydroxide (Na ⁺ ). NaOH) is produced. As a result, hydrochloric acid (HCl) as an inorganic acid is recovered from the acid chamber R2, and sodium hydroxide (NaOH) as an alkali is recovered from the alkali chamber R3. As the pure water introduced into the acid chamber R2 and the alkali chamber R3, the condensed water generated when the liquid to be treated is evaporated and concentrated in the concentration step S8 may be used.

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

The inorganic acid recovered from the acid chamber R2 (hydrochloric acid in the present embodiment) is not particularly limited, but is supplied to the acid elution tank 1 to leach the waste lithium ion battery in the acid elution step S1. It is preferable to reuse it as an acid. Further, it is preferable to supply the polyvalent cation removing device 4 and reuse it as a regenerating liquid for the chelate resin or ion exchange resin used in the impurity treatment step S7.

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

According to the lithium recovery method of the present embodiment described above, the liquid to be treated is evaporated and concentrated in the concentration step S8 before the carbonation step S10 to reduce the amount of the liquid to be treated and reduce the lithium concentration in the liquid to be treated. It is increasing. Therefore, the recovery rate of lithium carbonate crystals can be satisfactorily improved in the carbonation step S10.

Further, in the carbonation step S10, when the temperature of the liquid to be treated is low, the inorganic salt (sodium chloride in the present embodiment) contained in the liquid to be treated crystallizes, so that the liquid to be treated is heated during carbonation. By raising the temperature of the liquid to be treated higher than the evaporation temperature, the solubility of the inorganic salt remaining in the liquid to be treated is increased, and crystallization of the inorganic salt can be suppressed during carbonation. Further, if the temperature of the liquid to be treated is high during carbonation, the solubility of lithium carbonate decreases and the amount of lithium carbonate crystals recovered increases. Therefore, it is possible to obtain high-purity lithium carbonate with high efficiency.

Further, according to the lithium recovery method of the present embodiment, the first pH adjustment tank 2, the second pH adjustment tank 3, and the evaporation concentrator device are used without discarding the liquid to be treated after recovering the lithium carbonate crystals in the carbonation step S10. Lithium remaining in the liquid to be treated is recovered by circulating it in the system such as 5. Therefore, lithium can be recovered with a high recovery rate.

Further, according to the lithium recovery method of the present embodiment, the crystals of the inorganic salt (sodium chloride in this embodiment) contained in the precipitate separated from the solution to be treated in the solid-liquid separation step S9 are dissolved in the dissolution step S12. By performing bipolar membrane electrodialysis in the electrodialysis step S13 after preparing the inorganic salt solution, the inorganic acid and alkali are recovered from the inorganic salt solution, and the dilute inorganic salt solution after desalting is evaporated in the concentration step S8. After concentration, lithium contained in the dilute inorganic salt solution is recovered in the carbonization step S10. Therefore, lithium can be recovered with a high recovery rate. Further, the inorganic acids and alkalis recovered in the electrodialysis step S13 are circulated and reused in the acid elution step S1, the pH adjustment step S3, S5, and the impurity removal step S7, so that each step S1, S3, S5, S7 The amount of inorganic acid or alkali used in the above can be reduced.

Further, according to the lithium recovery method of the present embodiment, multivalent cations such as calcium and magnesium contained in the liquid to be treated are removed in the impurity removing step S7. As a result, the amount of impurities in the filtrate obtained in the solid-liquid separation step S11 after the carbonation step S10 is reduced, so that most of the liquid to be treated after the solid-liquid separation step S11 can be circulated in the system again. it can. Therefore, more lithium remaining in the liquid to be treated after the solid-liquid separation step S11 can be recovered, so that lithium can be recovered at a high recovery rate. Further, since the amount of impurities in the inorganic solution electrodialyzed in the electrodialysis step S13 is also reduced, it is possible to prevent the cation exchange membrane of the bipolar electrodialysis apparatus 9 from deteriorating due to scaling, and the performance of the bipolar membrane is maintained high. can do.

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

Although one embodiment of the lithium recovery method of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

For example, in the lithium recovery method of the above embodiment, the impurity removing step S7 for removing at least calcium and / or magnesium from the solution to be treated before the concentration step S8 is performed, but instead of or in addition to this. , The impurity removing step of removing at least calcium and / or magnesium from the inorganic salt solution before the electrodialysis step S13 may be performed in the same manner.

Further, in the lithium recovery method of the above embodiment, the alkali recovered in the electrodialysis step S13 is supplied to the first pH adjusting step S3 and the second pH adjusting step S5, but it is configured to be supplied to only one of them. May be good.

Further, in the lithium recovery method of the above embodiment, the pH adjusting steps S3 and S5 include the first pH adjusting step S3 and the second pH adjusting step S5, but three or more depending on the components contained in the waste lithium ion battery. The process may be configured to include the above steps, or may be configured to include only one step.

Further, in the lithium recovery method of the above embodiment, as shown in FIGS. 4 and 5, a treatment for removing impurities such as silica contained in the inorganic salt solution after the dissolution step S12 and before the electrodialysis step S13. The process may be performed. This treatment step can be performed in place of the impurity removing step S7 or in addition to the impurity removing step S7.

Specifically, first, in the recrystallization step S12-1, the inorganic salt (sodium chloride in this embodiment) contained in the inorganic salt solution is recrystallized. The method for recrystallizing the inorganic salt contained in the inorganic salt solution is not particularly limited, and for example, evaporation crystallization by the evaporation crystallization apparatus 10 can be used. In evaporation crystallization, the inorganic salt solution is heated to evaporate the solvent, and the concentration of the inorganic salt is increased to precipitate the crystals of the inorganic salt. The evaporation of the inorganic salt solution is preferably performed under a low pressure lower than the atmospheric pressure. In the evaporation crystallization, the inorganic salt contained in the inorganic salt solution may be crystallized by using the evaporation concentration device 5 without installing the evaporation crystallization device 10 separately.

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

Then, in the redissolving step S12-3, the recovered inorganic salt crystals are dissolved in the redissolving tank 11 with, for example, water so as to have a desired concentration, and the inorganic salt solution is regenerated. The temperature at this time is not particularly limited as long as it can dissolve the crystals of the inorganic salt. The water used for dissolving the inorganic salt is not particularly limited, but it is preferable to use the condensed water generated when the liquid to be treated is evaporated and concentrated in the concentration step S8, whereby the condensed water is used. Effective use is possible. The regenerated inorganic salt solution is supplied to the bipolar membrane electrodialysis apparatus 9. The impurities removed from the inorganic salt solution in the recrystallization steps S12-1 to the redissolution step S12-3 may contain calcium and / or magnesium in addition to silica.

In the embodiment of FIGS. 4 and 5, the silica contained in the inorganic salt solution is removed before the electrodialysis step S13. As a result, the amount of impurities in the inorganic solution electrodialyzed in the electrodialysis step S13 is also reduced, so that the performance of the bipolar film can be maintained high. Further, when the dilute inorganic salt solution (desalting solution) after the electrodialysis step S13 is supplied to the evaporation concentrator 5 and evaporated and concentrated again in the concentration step S8, the amount of impurities in the desalting solution is reduced. In the concentration step S8, it is possible to prevent scale from being generated and adhering to the heat transfer surface of the heat exchanger of the evaporation concentration device 5. Moreover, since the amount of impurities in the filtrate obtained by the solid-liquid separation step S11 after the carbonation step S10 is reduced, most of the liquid to be treated after the solid-liquid separation step S11 can be circulated in the system again. .. Therefore, more lithium remaining in the liquid to be treated after the solid-liquid separation step S11 can be recovered, so that lithium can be recovered at a high recovery rate.

Further, in the lithium recovery method of the above embodiment, as shown in FIGS. 6 and 7, a roasting step S0 for roasting the waste lithium ion battery may be further provided before the acid elution step S1. In the roasting step S0, the method of roasting the waste lithium ion battery is not particularly limited, and a known roasting apparatus 12 can be used.

In the embodiment of FIGS. 6 and 7, the exhaust gas generated in the roasting apparatus 12 (roasting step S0) is supplied to the carbonation tank 7, and the exhaust gas is mixed with the liquid to be treated as carbon dioxide in the carbonation step S10. doing. As a result, the amount of carbon dioxide gas used in the carbonation step S10 can be reduced. In addition, the liquid to be treated can be heated in the carbonation step S10. Needless to say, also in the embodiments of FIGS. 4 and 5, the roasting step S0 for roasting the waste lithium ion battery before the acid elution step S1 can be executed.

Further, the lithium recovery method of the above embodiment is an example of recovering lithium from a waste lithium ion battery, but the present invention is not limited to the method used for recovering lithium from a waste lithium ion battery. ..

S0 Roasting step S1 Acid elution step S3 First pH adjustment step (pH adjustment step)
S5 Second pH adjustment step (pH adjustment step)
S7 Impurity removal step S8 Concentration step S9 Solid-liquid separation step S10 Carbonation step S11 Solid-liquid separation step S12 Dissolution step S12-1 Recrystallization step S12-3 Relysis step S13 Electrodialysis step

Claims (7)

A concentration step in which a liquid to be treated in which at least lithium and an inorganic salt are dissolved is heated at a low pressure lower than atmospheric pressure to evaporate and concentrate.
A carbonation step of mixing carbon dioxide gas into the liquid to be treated after the concentration step and / or adding a water-soluble carbonate, and
A solid-liquid separation step of separating a precipitate containing lithium carbonate crystals precipitated by the carbonation step from the liquid to be treated is included.
A lithium recovery method in which the temperature of the liquid to be treated is equal to or higher than the evaporation temperature of the liquid to be treated in the concentration step in the carbonation step. The lithium recovery method according to claim 1, wherein in the concentration step, the liquid to be treated is evaporated and concentrated under a pressure of 10 kPa or more and 70 kPa or less. The lithium recovery method according to claim 1 or 2, wherein at least a part of the liquid to be treated after the solid-liquid separation step is evaporated and concentrated in the concentration step. In the concentration step, the inorganic salt contained in the liquid to be treated is precipitated as crystals.
A dissolution step of dissolving an inorganic salt contained as crystals in a precipitate separated from a liquid to be treated after the concentration step to form an inorganic salt solution, and a dissolution step.
Claims 1 to 3 further include an electrodialysis step of separating and recovering an inorganic acid together with an alkali from the inorganic salt solution by performing bipolar membrane electrodialysis on the inorganic salt solution obtained by the dissolution step. The lithium recovery method according to any one of. Before the concentration step,
An acid elution process in which a waste lithium-ion battery is leached with an inorganic acid to elute lithium,
Further including a pH adjusting step of adding an alkali to the lithium-containing liquid obtained by the acid elution step to adjust the pH.
The lithium recovery method according to any one of claims 1 to 4, wherein a liquid to be treated is produced by separating the precipitate precipitated by the pH adjusting step from the lithium-containing liquid. The lithium recovery method according to claim 5, wherein at least a part of the liquid to be treated after the solid-liquid separation step is reused as an alkali added in the pH adjustment step. Citing claim 4, wherein the alkali recovered in the electrodialysis step is reused as an alkali added in the pH adjustment step, and the inorganic acid recovered in the electrodialysis step is reused as an inorganic acid used in the acid elution step. The lithium recovery method according to claim 5 or 6.

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