JP7158332B2 - Method for concentrating lithium and method for producing lithium hydroxide - Google Patents

Description

This specification discloses a technique related to a method for concentrating lithium by solvent extraction and a method for producing lithium hydroxide using the same.

For example, in the process of recovering valuable metals from lithium ion secondary battery waste or various electronic devices, or in the treatment of salt lake brine or ore, a lithium solution in which lithium is dissolved may be obtained.

The lithium solution can be subjected to solvent extraction of lithium ions and back extraction from the solvent into the aqueous phase, thereby concentrating the lithium contained therein. The back-extracted liquid obtained after the back-extraction may be carbonated by addition of carbonate or blowing of carbon dioxide gas. In this case, lithium is recovered as lithium carbonate.
Such treatments for the lithium solution are described in Patent Documents 1 to 3, for example.

JP 2010-180439 A U.S. Patent Application Publication No. 2011/0135547 Japanese Patent No. 5706457

Incidentally, sodium may be contained in the solvent used to extract lithium ions from the lithium solution because it originally exists in the lithium solution or is contained in the reagent used for extraction. Since this sodium becomes an impurity in lithium carbonate and other lithium compounds to be finally obtained and lowers the purity thereof, it is required to be sufficiently removed during the treatment up to that point.

This specification discloses a method for concentrating lithium and a method for producing lithium hydroxide, which can effectively remove sodium by solvent extraction.

The lithium concentration method disclosed in this specification is a method of concentrating lithium by solvent extraction, comprising a scrubbing step of scrubbing a solvent containing lithium ions and sodium ions used for extracting lithium ions with a lithium solution; a back extraction step of back extracting lithium ions from the solvent after the scrubbing step, wherein the scrubbing step removes sodium ions from the solvent containing lithium ions and sodium ions .

Further, the method for producing lithium hydroxide disclosed in this specification is a method for producing lithium hydroxide using the above lithium concentration method, wherein It has a neutralization step of neutralizing the concentrate with hydroxide.

According to the lithium concentration method described above, sodium can be effectively removed by solvent extraction.

FIG. 2 is a flow diagram showing an example of a method for producing lithium hydroxide using the lithium concentration method of one embodiment. FIG. 2 is a flow chart showing an example of specific solvent and liquid flows in the lithium concentration method of one embodiment. FIG. 4 is a flow diagram showing another example of specific solvent and liquid flows in the lithium enrichment method of one embodiment. 4 is a graph showing the relationship between the number of scrubbing stages and the concentration of Na ions in the post-backextraction liquid in Examples.

Hereinafter, embodiments disclosed in this specification will be described in detail.
In one embodiment of the lithium concentration method, in concentrating lithium by solvent extraction, a scrubbing step of scrubbing a solvent containing lithium ions and sodium ions used for extracting lithium ions with a lithium solution, and a scrubbing step. and a back extraction step of back extracting lithium ions from the solvent after passing through.

In many cases, the scrubbing step is preceded by an extraction step of extracting the lithium ions from the lithium solution into a solvent to obtain a solvent containing lithium ions and sodium ions as described above. If the lithium solution contains sodium ions, the sodium ions in the lithium solution can also be extracted into the solvent together with the lithium ions in the extraction step. As a result, the solvent used in the extraction step may contain sodium ions derived from the lithium solution. Moreover, the solvent may contain sodium ions due to the pH adjuster used in the extraction step. There is no particular limitation on the route of mixing sodium ions into the solvent.

Incidentally, if lithium hydroxide is to be produced from a lithium solution, it is the mainstream to remove impurities using an electrodialysis method or an isolation method. However, electrodialysis requires expensive dialysis membranes and high operating costs. In addition, since the isolation method targets a relatively dilute solution, a separate and further concentration treatment is required. In addition, the lithium solution obtained from the lithium ion secondary battery waste as described above has a higher concentration of impurity components than natural raw materials due to its positive electrode material and the like. There is a concern that impurities cannot be separated effectively. On the other hand, in this embodiment, lithium can be effectively concentrated at a relatively low cost by using a solvent extraction method, details of which will be described later.

(lithium solution)
The lithium solution is not particularly limited as long as it contains lithium ions and sodium ions, but it can be obtained by a process of recovering valuable metals from lithium ion secondary battery waste. Specifically, as exemplified in FIG. 1, lithium ion secondary battery waste is processed by roasting or the like as necessary, and then lithium contained therein is dissolved with water or an acid solution. Thereby, a lithium solution is obtained. The residue produced here can be used in processes for recovering valuable metals such as cobalt and nickel by acid leaching, neutralization and solvent extraction.

In addition, the lithium ion secondary battery has a housing containing aluminum as an exterior that envelops its periphery. Examples of this housing include those made only of aluminum, those containing aluminum and iron, aluminum laminates, and the like. In addition, the lithium-ion secondary battery has a positive electrode active layer composed of a single metal oxide selected from the group consisting of lithium, nickel, cobalt and manganese, or a composite metal oxide of two or more types, etc., in the housing. The material, or cathode active material, may include aluminum foil (cathode substrate) that is coated and adhered by, for example, polyvinylidene fluoride (PVDF) or other organic binder or the like. In addition, the lithium ion secondary battery may contain copper, iron, and the like. Furthermore, lithium-ion secondary batteries usually contain an electrolytic solution within the housing. As the electrolytic solution, for example, ethylene carbonate, diethyl carbonate, etc. may be used.

In particular, the lithium ion concentration in the lithium solution obtained from the lithium ion secondary battery waste as described above is, for example, 0.5 g/L to 2.3 g/L, typically 1.0 g/L. ~2.0 g/L. Also, the sodium ion concentration in the lithium solution is, for example, 0.1 g/L to 40.0 g/L, typically 10.0 g/L to 20.0 g/L.
However, this embodiment can be applied not only to the process of recovering valuable metals from lithium ion secondary battery waste but also to various processes having a step of concentrating lithium by solvent extraction.

(Extraction process)
In the extraction step, lithium ions in the lithium solution are extracted into a solvent. As a result, cobalt, nickel, fluorine, and the like that may be contained in the lithium solution remain on the liquid side, and these can be separated from lithium. In the case of a lithium solution containing sodium ions, not only lithium ions but also sodium ions can be extracted to some extent from the lithium solution.

Specifically, the extraction is performed, for example, by contacting a lithium solution (aqueous phase) and a solvent (organic phase), stirring and mixing them with a mixer, and transferring lithium ions and the like in the lithium solution to the solvent. After that, the settler separates the organic phase and the aqueous phase based on the difference in specific gravity. The O/A ratio, which is the volume ratio of the organic phase to the aqueous phase, can be greater than 1.5/1.0, depending on the lithium ion concentration and other conditions. In order to increase the extraction rate of lithium ions, the O/A ratio can be adjusted and the number of extraction stages can be increased.

Here, for the lithium dissolution solution, as the extractant that is the solvent, a phosphonate extractant alone, a phosphate ester extractant alone, or a phosphonate ester extractant and a phosphate ester extractant are used. Mixed extractants can be used. As the phosphonate extractant, 2-ethylhexyl 2-ethylhexylphosphonate (trade name: PC-88A, Ionquest 801) is preferable from the viewpoint of separation efficiency between nickel and cobalt. Examples of the phosphate extractant include di-2-ethylhexyl phosphate (trade name: D2EHPA or DP8R).

The extractant can be diluted with an aromatic, paraffinic, naphthenic, or other hydrocarbon organic solvent, if necessary, before use. In this case, the concentration of the extractant can be, for example, 15% to 35% by volume.

The pH during extraction is preferably 7-8. This is because if the pH is less than 7, the lithium extraction rate may be low and phase separation may be poor. and the diluent may separate. From this point of view, it is more preferable to set the pH at the time of extraction to 7.2 to 7.5.

A pH adjuster such as sodium hydroxide, lithium hydroxide, aqueous ammonia, or other alkaline solutions can be used to adjust the pH during extraction. Among them, sodium hydroxide is preferred because it is less expensive than other reagents and has no odor. Moreover, even if sodium hydroxide is added as a pH adjuster, the resulting sodium ions can be effectively removed in the scrubbing step, which will be described later. When lithium hydroxide is used as a pH adjuster, addition in the form of powder is not preferable for solvent extraction, but when adding as a solution, the pH may not be adjusted unless the lithium concentration in the solution is high to some extent. be.

(Scrubbing process)
The above extraction step yields a solvent containing lithium ions and sodium ions. In the next scrubbing step, this solvent is scrubbed with a lithium solution. The purpose of this scrubbing step is to remove the sodium ions that have been extracted into the solvent.

It is important here to scrub with a lithium solution containing lithium ions. By adjusting the lithium ion concentration in the lithium solution or the like, the sodium ions in the solvent can be effectively removed because the lithium ions in the lithium solution are replaced with the sodium ions in the solvent. At this time, lithium ions and sodium ions are generally substituted in the same number of moles. Therefore, if the number of moles of lithium ions in the lithium solution is equal to or greater than the number of moles of sodium ions in the solvent, the sodium ions in the solvent can be removed more effectively.

The lithium ion concentration in the lithium solution used for scrubbing is preferably 1.0 g/L to 10.0 g/L, more preferably 1.0 g/L to 5.0 g/L. If the lithium ion concentration in the lithium solution is too low, there is concern that removal of sodium ions in the solvent will be insufficient. On the other hand, if the lithium ion concentration is too high, it may exceed the amount of lithium ions required to remove the sodium ions in the solvent. In this case, if the post-scrubbing solution were to bleed off, lithium would be lost. In addition, the loss of lithium makes it difficult to circulate lithium in the system and effectively use it repeatedly, as will be described later, which is undesirable because it requires the supply of a separate lithium source.

During scrubbing, it is preferable to adjust the pH of the mixture of the solvent and the lithium solution to 5.0 to 9.0, and further to adjust the pH to 6.0 to 8.0. is even more preferable. If the pH is too low, the concentration efficiency of the back extraction process may decrease, while if it is too high, the extractant and diluent may separate during scrubbing.

The number of scrubbing stages, the O/A ratio, and the like can be appropriately determined according to the liquid composition, such as the Li/Na concentration ratio of the liquid after back extraction, which will be described later.

As the lithium solution used in the scrubbing step, as shown in FIG. 2, an unused lithium solution can be used, or a back-extraction liquid obtained in the back-extraction step described later can also be used. When the post-back extraction liquid is used as a lithium solution in the scrubbing step, some of the lithium ions in the lithium solution replace sodium ions in the solvent, are contained in the solvent, and are sent to the back extraction step. Although the rest of the lithium ions remain in the post-scrubbing solution, the post-scrubbing solution is returned to the extraction step by, for example, being mixed with the lithium solution as shown in FIG. can be done. This makes it possible to recover most of the lithium while making effective use of it. The post-scrubbing solution can also be subjected to another scrubbing step as a lithium solution. In this case, lithium can be circulated within the system and used repeatedly.
However, when the liquid is circulated in this manner, sodium is concentrated therein, so that the scrubbed liquid can be periodically bleed off as shown in FIG.

Through the scrubbing process, the sodium ion concentration in the solvent can be preferably reduced to 1 mg/L or less.

(Reverse extraction process)
Thereafter, a back-extraction step is performed to back-extract lithium ions contained therein from the solvent that has undergone the scrubbing step. In the back extraction step, for example, the pre-back extraction liquid, which is an acidic aqueous solution, is stirred and mixed with a mixer or the like. As a result, the lithium ions contained in the solvent are transferred to the aqueous phase.

The pre-back-extraction solution used in the back-extraction process may be any inorganic acid such as sulfuric acid, hydrochloric acid, nitric acid, etc. Among them, sulfuric acid is preferred. This is because the use of sulfuric acid turns the back-extracted solution into a lithium sulfate solution, which can be used as a raw material for lithium hydroxide.

In the back extraction step, the pH is maintained preferably within the range of 0.5-2.0, more preferably within the range of 1.0-1.5. If the pH at the time of back extraction is out of the range and becomes low, there is a risk that the amount of the pH adjuster at the time of extraction will increase. Moreover, when the pH exceeds the range, there is concern that lithium ions may remain in the solvent. If back extraction is performed in multiple stages, the pH may increase as the number of stages is increased. It is preferable to manage
Other conditions are appropriately set, but the O/A ratio can be, for example, 1.0 or more, preferably 1.0 to 1.5.

As shown in FIG. 2, the post-back-extraction liquid (lithium concentrate) obtained in the back-extraction step can be further subjected to the back-extraction step as a pre-back-extraction liquid, thereby further increasing the lithium ion concentration. can. Further, as described above, the post-back extraction liquid can also be used in the scrubbing step as a lithium solution.

The post-back extraction liquid has a lithium ion concentration of, for example, 10 g/L to 30 g/L, typically 20 g/L to 25 g/L. Also, the sodium ion concentration in the post-back extraction liquid is preferably 3 mg/L or less, more preferably 1 mg/L or less.
The back-extraction liquid can be used for producing lithium carbonate by a known method, but here, an example of a method for producing lithium hydroxide using the back-extraction liquid will be described below.

(Neutralization process)
In the neutralization step, the lithium concentrated liquid as the post-reverse extraction liquid is neutralized with a hydroxide other than lithium hydroxide, and lithium hydroxide is obtained by thermal concentration or vacuum distillation. Lithium hydroxide has a lower melting point than lithium carbonate, and may be suitably used as a raw material for positive electrode materials.

More specifically, hydroxide is added to the lithium concentrate to raise the pH, preferably to 10-12. A low pH may result in insufficient removal of impurities, while a high pH may cause re-dissolution when amphoteric metals are contained. In the case of concentration by heating, the liquid temperature can be, for example, 50°C to 100°C.

Examples of hydroxides other than lithium hydroxide include barium hydroxide. Among these, barium hydroxide is preferable because it can be formed into a lithium hydroxide liquid by a chemical conversion reaction with lithium sulfate.

The lithium hydroxide thus produced has a sufficiently reduced sodium content. For example, the sodium content in lithium hydroxide is for example less than 100 ppm by weight, typically less than 10 ppm by weight.

Next, the lithium concentration method as described above was carried out on a trial basis, and the effect was confirmed, which will be described below. However, the description herein is for illustrative purposes only and is not intended to be limiting.

PC-88A was diluted to 25% as an extractant for the lithium solution containing 2000 mg/L of Li ions and 10 mg/L of Na ions obtained from lithium ion secondary battery waste as described above. 25% NaOH as a pH adjuster was used to adjust the pH to 7, and one-stage extraction was performed at an O/A ratio of 2/1. The Li extraction rate during extraction was 95%.

The solvent obtained by the above extraction was scrubbed for the purpose of removing Na, and then back-extracted. In the scrubbing, a lithium hydroxide aqueous solution having a Li ion concentration of 5 g/L was used as the lithium solution, and the pH was adjusted to 7. Back extraction was performed with 100 g/L H2SO4, O/ _A = _1/1 .

FIG. 4 graphically shows the relationship between the number of scrubbing stages and the concentration of Na ions in the liquid after back extraction. From FIG. 4, it can be seen that Na was effectively removed by scrubbing because the concentration of Na ions in the liquid after back extraction decreased by adjusting the number of scrubbing stages and the O/A ratio. Also, it is considered possible to improve the Na separation efficiency by increasing the Li ion concentration in the lithium solution used for scrubbing, lowering the pH during scrubbing, or the like.

After 6 stages of scrubbing, the pH was adjusted to <1.0 with sulfuric acid at an O/A ratio of 2/1, and 1 stage of back extraction was performed. As a result, Table 1 shows the Li ion concentration and the Na ion concentration in the liquid after back extraction at each time when the back extraction was repeated.
Table 2 shows the same results of back extraction under the same conditions, except that no scrubbing was performed.
As shown in Tables 1 and 2, in Table 1 with scrubbing, the concentration of Na ions in the liquid after back extraction was 1/3000 or less, indicating that Na was effectively removed by scrubbing.

From the back-extracted solution (lithium sulfate solution) obtained by scrubbing as described above, lithium hydroxide is removed by the reaction of lithium sulfate and barium hydroxide (Li ₂ SO ₄ +Ba(OH) ₂ →2LiOH+BaSO ₄ ). Obtained. Table 3 shows the grade of this lithium hydroxide. As a result, it was confirmed that the Na grade in lithium hydroxide was low.

Claims (12)

A method of concentrating lithium by solvent extraction, comprising:
A scrubbing step of scrubbing a solvent containing lithium ions and sodium ions used for extracting lithium ions with a lithium solution, and a back extraction step of back extracting lithium ions from the solvent after the scrubbing step ,
A method for concentrating lithium , wherein the scrubbing step removes sodium ions from the solvent containing lithium ions and sodium ions . The method for concentrating lithium according to claim 1, wherein in the scrubbing step, the pH of the mixture of the solvent and the lithium solution is adjusted to 6.0 to 8.0. 3. The method for concentrating lithium according to claim 1, wherein the lithium solution having a lithium ion concentration of 1.0 g/L to 10.0 g/L is used in the scrubbing step. The method for concentrating lithium according to any one of claims 1 to 3, wherein sulfuric acid is used for back extraction of lithium ions in the back extraction step. The lithium concentration method according to any one of claims 1 to 4, further comprising an extraction step of extracting lithium ions from the lithium solution to obtain the solvent containing lithium ions and sodium ions before the scrubbing step. 6. The method for concentrating lithium according to claim 5, wherein in the extraction step, an alkaline solution is used as a pH adjuster to adjust the pH to 7-8. 4. The extracting step uses, as an extractant, a phosphonate ester-based extractant, a phosphate ester-based extractant, or a mixture of a phosphonate ester-based extractant and a phosphate ester-based extractant. 7. The method for concentrating lithium according to 5 or 6. The method for concentrating lithium according to any one of claims 1 to 7 , wherein a post-back extraction liquid obtained in the back extraction step is used as the lithium solution in the scrubbing step. The method for concentrating lithium according to any one of claims 1 to 8 , wherein the back extraction step is carried out at a pH of 0.5 to 2.0. A method for producing lithium hydroxide using the lithium concentration method according to any one of claims 1 to 9 ,
A method for producing lithium hydroxide, comprising a neutralization step of neutralizing a lithium concentrated liquid, which is a post-back extraction liquid obtained in the back extraction step, with a hydroxide. 11. The method for producing lithium hydroxide according to claim 10 , wherein the hydroxide is barium hydroxide. The solvent containing lithium ions and sodium ions in the scrubbing step is obtained by extracting lithium ions from a lithium solution,
12. The method for producing lithium hydroxide according to claim 10 or 11 , wherein the lithium solution is obtained by leaching with water or an acid solution after roasting a recycled lithium ion battery raw material.

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