JP7365846B2 - Method for producing high purity cobalt sulfate solution and method for producing cobalt sulfate - Google Patents

Description

This specification discloses a method for producing a high-purity cobalt sulfate solution and a technique related to a method for producing cobalt sulfate.

Cobalt is generally used as a positive electrode active material for lithium ion batteries, cobalt alloys, and various other uses. In such applications, nickel is often used along with cobalt. For example, some lithium ion batteries include a so-called ternary positive electrode active material containing cobalt and nickel.

When lithium-ion batteries containing cobalt and nickel as positive electrode active materials are discarded due to product lifespan, manufacturing defects, or other reasons, various metals such as cobalt and nickel are recovered from the waste lithium-ion battery scrap. This is being widely considered.

Patent Document 1 describes that lithium ion battery scrap is subjected to pretreatment such as roasting, crushing, and sieving, and then brought into contact with an acid to be leached, and metals are recovered from the leached liquid. ing. More specifically, a phosphonic acid ester extractant such as 2-ethylhexyl 2-ethylhexylphosphonate is applied to the extraction residual liquid containing cobalt ions and nickel ions obtained after performing a predetermined solvent extraction on the post-leaching liquid. The cobalt ions will be extracted into a solvent using a solvent, and the cobalt ions will be back extracted from the solvent using sulfuric acid or the like, and the cobalt will be recovered by electrowinning.

Japanese Patent Application Publication No. 2016-186118

In the above solvent extraction as described in Patent Document 1, cobalt ions in the extraction residue are mainly extracted, but a small amount of nickel ions in the extraction residue are also extracted and included in the solvent. Further, in the subsequent back extraction, not only cobalt ions contained in the solvent but also nickel ions are transferred to the aqueous phase. Therefore, the resulting cobalt sulfate solution contains not only cobalt ions but also nickel ions, albeit in relatively small amounts. In addition, such a cobalt sulfate solution may not meet the requirements for cobalt purity when used for a specific purpose, such as the manufacture of lithium ion batteries.

Note that even if electrowinning is performed using the above-mentioned cobalt sulfate solution as an electrolyte, nickel ions in the cobalt sulfate solution will also be deposited on the electrode, so that the electrolytic cobalt will contain nickel. Therefore, when the electrolytic cobalt is dissolved in sulfuric acid, it becomes a cobalt sulfate solution containing nickel ions, and in this case as well, the purity of cobalt in the cobalt sulfate solution is not sufficiently high.

This specification discloses a method for producing a high-purity cobalt sulfate solution and a method for producing cobalt sulfate that can effectively increase the purity of cobalt in a cobalt sulfate solution containing a relatively small amount of nickel ions.

The method for producing a high-purity cobalt sulfate solution disclosed in this specification is a method for producing a high-purity cobalt sulfate solution having a higher purity of cobalt than the cobalt sulfate solution from a cobalt sulfate solution containing nickel ions. , the cobalt sulfate solution has a cobalt/nickel concentration ratio of 100 or more, and the cobalt sulfate solution is brought into contact with a solvent containing bis(2,4,4-trimethylpentyl)phosphinic acid to adjust the pH; The method includes a nickel separation step of extracting the cobalt ions into the solvent while leaving the nickel ions in the cobalt solution in the solution, and then back-extracting the cobalt ions extracted into the solvent with sulfuric acid, before the nickel separation step. The method further includes a cobalt extraction step of extracting cobalt ions from an acidic solution containing cobalt ions and nickel ions into a solvent, and back-extracting the cobalt ions in the solvent with sulfuric acid to obtain the cobalt sulfate solution.

The method for producing cobalt sulfate disclosed in this specification includes a crystallization step of crystallizing cobalt ions in a high-purity cobalt sulfate solution produced by the above-described method for producing a high-purity cobalt sulfate solution to obtain cobalt sulfate. It is something that

According to the method for producing a high-purity cobalt sulfate solution described above, the purity of cobalt in a cobalt sulfate solution containing a relatively small amount of nickel ions can be effectively increased.

FIG. 2 is a flow diagram illustrating an example of a method for producing cobalt sulfate, including a method for producing a high-purity cobalt sulfate solution according to one embodiment. FIG. 2 is a flow diagram showing an example of pretreatment for lithium ion battery scrap when obtaining a cobalt sulfate solution used in the method for producing a high-purity cobalt sulfate solution in FIG. 1. FIG. FIG. 3 is a flow diagram showing an example of wet processing for the battery powder obtained in the pretreatment of FIG. 2. FIG. FIG. 4 is a flow diagram showing an example of a process for the cobalt extraction residual liquid obtained in the cobalt extraction step of the wet process in FIG. 3. FIG. It is a graph showing the relationship between the Ni concentration of the aqueous phase after extraction and the Ni concentration of the organic phase after extraction at pH: 4.5 in an example. It is a graph showing the relationship between the Ni concentration of the aqueous phase after extraction and the Ni concentration of the organic phase after extraction at pH: 5.0 in an example. It is a graph showing the relationship between the Ni concentration of the aqueous phase after extraction and the Ni concentration of the organic phase after extraction at pH: 5.5 in Example.

Below, embodiments of the method for producing a high-purity cobalt sulfate solution disclosed in this specification will be described in detail.
In the method for producing a high-purity cobalt sulfate solution according to one embodiment, as shown in FIG. A high-purity cobalt sulfate solution with higher cobalt purity than the solution is produced. In the nickel separation step, nickel ions in the cobalt sulfate solution can be effectively separated by performing predetermined extraction and back extraction using a solvent extraction method. In addition, when a crystallization step is further performed on a highly purified cobalt sulfate solution, cobalt sulfate, which is a solid cobalt sulfate with a low nickel content, can be produced.

(Cobalt sulfate solution)
The cobalt sulfate solution used in the nickel separation process also contains cobalt ions and a relatively small amount of nickel ions. Specifically, the target is a cobalt sulfate solution in which the cobalt/nickel concentration ratio, which is the ratio of the cobalt concentration to the nickel concentration of the cobalt sulfate solution, is 100 or more. The cobalt/nickel concentration ratio of the cobalt sulfate solution is typically 100-1000.

The nickel concentration of the cobalt sulfate solution is, for example, 0.05 g/L to 0.90 g/L, typically 0.10 g/L to 0.60 g/L. The cobalt concentration of the cobalt sulfate solution is, for example, from 5 g/L to 90 g/L, typically from 5 g/L to 30 g/L, more typically from 10 g/L to 15 g/L.
In addition, the cobalt sulfate solution may contain, for example, sodium ions in an amount of 0.01 g/L to 0.05 g/L.

The cobalt sulfate solution can be obtained, for example, by subjecting lithium ion battery scrap to pretreatment and wet treatment as described below with reference to FIGS. The manufacturing method is not particularly limited as long as the cobalt/nickel concentration ratio is 100 or more.

(Nickel separation process)
In the nickel separation step, the above cobalt sulfate solution is subjected to extraction and back extraction using a solvent extraction method. Here, in order to effectively extract and back-extract the cobalt ions in the cobalt sulfate solution while preventing the nickel ions in the cobalt sulfate solution from being extracted as much as possible, bis(2,4,4-trimethylpentyl)phosphinic acid was used. (phosphonic acid) is used.

When a solvent containing an extractant containing bis(2,4,4-trimethylpentyl)phosphinic acid is used, cobalt ions can be extracted into the solvent while leaving nickel ions in the cobalt sulfate solution. Specifically, such an extractant is particularly preferably ALBRITECT TH1 (trade name) or Cyanex 272 (trade name) manufactured by SOLVAY, but is not limited thereto. This results in cobalt and nickel extraction curves that are well separated on the low and high pH sides compared to extractants such as mono-2-ethylhexyl (2-ethylhexyl)phosphinate (PC-88A, Ionquest 801). As a result, the range in which cobalt ions are extracted but nickel ions are not extracted is expanded. In other words, selective extraction of only cobalt ions becomes easy.

The purity of the extractant containing bis(2,4,4-trimethylpentyl)phosphinic acid can be, for example, 95% or higher.
Such an extractant can be diluted to a concentration of 10% to 30% by volume using an aromatic, paraffinic, naphthenic, or other hydrocarbon organic solvent and used as a solvent. can.

An example of the extraction procedure is to bring a cobalt sulfate solution (aqueous phase) into contact with a solvent (organic phase) using the above extractant while adding a pH adjuster, and then mix the mixture with a mixer at 200 to 500 rpm for 5 to 60 minutes. Stir and mix for several minutes to allow the cobalt ions to react with the extractant. The liquid temperature at this time is 15°C to 60°C. Thereafter, a settler separates the mixed organic phase and aqueous phase based on the difference in specific gravity.
Solvent extraction may be carried out repeatedly, for example in a multistage manner in which the organic phase and the aqueous phase are brought into countercurrent contact. The O/A ratio (volume ratio of the organic phase to the aqueous phase) is generally 0.1 to 10.

The equilibrium pH during extraction is preferably 4.0 to 7.0, particularly preferably 5.0 to 6.0. This allows nickel ions to remain in the aqueous phase and cobalt ions to be effectively extracted into the organic phase. In other words, if the equilibrium pH at the time of extraction is low, cobalt ions will not be sufficiently extracted, whereas if the equilibrium pH is high, there is a concern that nickel ions will also be extracted. However, since the appropriate pH range varies depending on the combination of cobalt concentration, extractant volume fraction, oil/water phase ratio, temperature, etc., it may be outside the above range.

As the pH adjuster, various alkalis such as ammonia and sodium hydroxide can be used. Note that since ammonia requires equipment for its treatment, sodium hydroxide may be preferable.

After extraction, the organic phase containing cobalt ions is back-extracted with sulfuric acid. Back extraction can be performed by stirring and mixing using a mixer or the like at 200 to 500 rpm for 5 to 60 minutes using a back extraction liquid such as an acidic sulfuric acid solution. The acid concentration of the back extraction liquid is preferably adjusted to pH: 1.0 to 3.0, more preferably adjusted to pH: 1.5 to 2.5. Back extraction can be carried out at 15°C to 60°C or less.

By back extraction, cobalt ions move from the organic phase to the aqueous phase side, and a high purity cobalt sulfate solution can be obtained as a back extraction liquid (aqueous phase) containing cobalt ions. Here, as mentioned earlier, many nickel ions were left in the aqueous phase during extraction, so the high purity cobalt sulfate solution contains almost no nickel ions.

The cobalt concentration in the high purity cobalt sulfate solution will be, for example, from 1 g/L to 100 g/L, typically from 10 g/L to 90 g/L. Further, the nickel concentration in the high purity cobalt sulfate solution can preferably be 1 mg/L or less. The cobalt/nickel concentration ratio of the high purity cobalt sulfate solution is preferably 10,000 or more.

(Production of cobalt sulfate)
When producing cobalt sulfate, as shown in FIG. 1, the above-mentioned high-purity cobalt sulfate solution can be subjected to a crystallization step. In the crystallization step, a high-purity cobalt sulfate solution is heated to, for example, 40° C. to 50° C. and concentrated to crystallize cobalt as cobalt sulfate.

The high-purity cobalt sulfate solution has undergone the nickel separation process described above, so that nickel ions have been sufficiently reduced. Therefore, in this embodiment, it is not necessary to perform a cleaning step to remove impurities after the nickel separation step and before the crystallization step. Therefore, in this embodiment, the crystallization process can be performed on the high purity cobalt sulfate solution obtained in the nickel separation process without going through the cleaning process.

The cobalt sulfate produced in this way has a nickel content of preferably 10 mass ppm or less, more preferably 5 mass ppm or less, and since nickel has been sufficiently removed, it is suitable for use in lithium ion secondary batteries, etc. It can be effectively used as a raw material for manufacturing batteries.

(Processing of lithium ion battery scrap)
In order to obtain the above-described high-purity cobalt sulfate solution or cobalt sulfate solution used in the production of cobalt sulfate, for example, as shown in FIGS. 2 and 3, lithium ion battery scrap containing at least cobalt and nickel is processed to produce a battery A pretreatment to obtain a powder and a wet treatment to wetly process the battery powder to obtain the cobalt sulfate solution may be performed.

Lithium ion battery scrap is lithium ion batteries that can be used in mobile phones and various other electronic devices, and is discarded due to the battery product's lifespan, manufacturing defects, or other reasons. It is preferable to recover valuable metals from such lithium ion battery scraps from the viewpoint of effective utilization of resources. Lithium ion battery scrap may contain, for example, 0.1% to 40.0% by weight of cobalt and 0.1% to 15.0% by weight of nickel. In addition, lithium ion battery scrap may contain lithium, manganese, aluminum, copper, iron, etc.

Processing of lithium ion battery scrap may include a roasting process, a crushing process, and a sieving process as shown in FIG. 2 as pretreatment. This yields battery powder. In the roasting process, the lithium ion battery scrap is heated in various heating equipment such as a rotary kiln furnace, various other furnaces, and a furnace that heats in an atmospheric atmosphere, for example, to a temperature of 450°C to 1000°C, preferably 600°C to 800°C. It is preferred to hold the temperature in the temperature range of 0.5 to 4 hours.

The above battery powder can be subjected to wet processing. Wet processing includes a lithium leaching process, an acid leaching process, a neutralization process, a manganese/aluminum extraction process, a cobalt extraction process, etc., as shown in FIG. After the cobalt extraction step, the aforementioned lithium sulfate solution is obtained.

In the lithium leaching process, the battery powder is brought into contact with water to dissolve the lithium contained therein. Thereby, lithium contained in the battery powder can be separated at an early stage of the recovery process. Here, it is preferable to add an acid such as sulfuric acid to the water so that the pH of the lithium solution finally obtained is 7.0 to 10.0. In this case, elution of cobalt, aluminum, etc. can be suppressed, and mainly lithium can be selectively dissolved.

In the acid leaching step, the residue obtained in the above lithium leaching step is added to an acid such as sulfuric acid and leached. The acid leaching step can be carried out using known methods or conditions, but the pH of the acidic solution should be 0.0 to 2.0, and the oxidation-reduction potential (ORP value, silver/silver chloride potential standard) of the acidic solution should be It is preferable to set it to 0 mV or less.

In the neutralization step, an alkali such as sodium hydroxide, sodium carbonate, or ammonia is added to the post-leaching solution obtained in the acid leaching step to increase the pH. Thereby, aluminum in the post-leaching solution can be precipitated and removed. However, this neutralization step can also be omitted. In the neutralization step, it is preferable to set the pH to 4.0 to 6.0, the ORP value (ORPvsAg/AgCl) to -500 mV to 100 mV, and the liquid temperature to 50°C to 90°C.

In the manganese/aluminum extraction step, after the acid leaching step, or after the neutralization step if a neutralization step is performed, the remainder of aluminum and/or manganese is extracted and removed from the post-leaching solution or the post-neutralization solution. Here, it is preferable to use a mixed extractant containing a phosphate extractant and an oxime extractant. Here, examples of the phosphoric acid ester extractant include di-2-ethylhexyl phosphoric acid (trade name: D2EHPA or DP8R). The oxime extractant is preferably aldoxime or one containing aldoxime as a main component. Specifically, for example, 2-hydroxy-5-nonylacetophenone oxime (trade name: LIX84), 5-dodecylsalicyaldoxime (trade name: LIX860), a mixture of LIX84 and LIX860 (trade name: LIX984), 5- There are nonyl salicylaldoxime (trade name: ACORGAM 5640) and the like, and among these, 5-nonylsalicylaldoxime is preferred from the viewpoint of price. The equilibrium pH during extraction is preferably 2.3 to 3.5, more preferably 2.5 to 3.0. Note that the manganese/aluminum extraction step can also be omitted.

In the cobalt extraction step, cobalt ions are mainly extracted and back-extracted from the extraction residue (aqueous phase) of the manganese/aluminum extraction step. However, at this time, nickel ions are also extracted and back-extracted, although in small amounts, and are included in the back-extraction solution (cobalt sulfate solution).

In the cobalt extraction step, first, preferably, a phosphonic acid ester extractant such as mono-2-ethylhexyl (2-ethylhexyl)phosphinate (trade name: PC-88A, Ionquest 801) is used. The equilibrium pH during extraction is preferably 5.0 to 6.0, more preferably 5.2 to 5.7. Note that the cobalt extraction residual liquid (aqueous phase) after the extraction can be used for producing nickel sulfate, which will be described later.
The solvent (organic phase) from which the cobalt ions have been extracted is, if necessary, scrubbed using a scrubbing liquid such as a sulfuric acid acidic solution with a pH of preferably 4.0 to 5.0, more preferably 4.3 to 4.6. It can be provided to It is preferable that the number of times of scrubbing be one or more times and the O/A ratio be 1/2 to 1.5/1. Thereby, sodium ions in the solvent can be effectively removed.

Thereafter, back extraction is performed using sulfuric acid in a solvent containing cobalt ions. The pH is preferably in the range of 2.0 to 4.0, and even more preferably in the range of 2.5 to 3.5. Note that the O/A ratio and the number of times can be determined as appropriate. The liquid temperature may be room temperature, but is preferably 0°C to 40°C. After back-extraction, a cobalt sulfate solution is obtained as a post-back-extraction liquid.

(Production of nickel sulfate)
Nickel sulfate can be produced using the cobalt extraction residual liquid from the above-mentioned cobalt extraction step. In the production of nickel sulfate, as shown in FIG. 4, a nickel extraction process, an electrolysis process, a dissolution process, and a crystallization process are performed.

In the nickel extraction step, preferably a carboxylic acid extractant is used for the cobalt extraction residue to separate nickel ions from the cobalt extraction residue. Examples of the carboxylic acid extractant include neodecanoic acid and naphthenic acid, among which neodecanoic acid is preferred because of its ability to extract nickel ions. The equilibrium pH during extraction is preferably 6.0 to 8.0, more preferably 6.8 to 7.2.
After extraction, back extraction is performed on the organic phase containing nickel ions using a back extraction solution such as sulfuric acid, hydrochloric acid, or nitric acid. Here, the pH is such that 100% of nickel ions are extracted from the organic phase into the back extraction liquid (aqueous phase). Specifically, the pH is preferably in the range of 1.0 to 3.0, more preferably 1.5 to 2.5. Note that the O/A ratio and the number of times can be determined as appropriate, but the O/A ratio is 5/1 to 1/1, more preferably 4/1 to 2/1. By increasing the number of times of back extraction, the target metal concentration can be increased to a concentration that is advantageous for the electrolytic process.

In the electrolytic step, the back-extracted solution obtained in the nickel extraction step is used as an electrolytic solution, and nickel ions contained in the electrolytic solution are deposited on an electrode by electrolysis to obtain electrolytic nickel. The electrolytic step can be carried out under known conditions; for example, the liquid temperature is adjusted to 40°C to 60°C, the pH is adjusted to 1.5 to 2.0, and the current density is adjusted to 190A/m ² to 210A/m. Can be done as ² .

In the dissolution step, electrolytic nickel is dissolved with an acid such as sulfuric acid or sulfuric acid and an oxidizing agent to obtain a nickel solution. The pH at the end of this dissolution can be, for example, 1.0 to 5.0, preferably 2.0 to 4.0. The nickel concentration in the nickel solution is, for example, 10 g/L to 150 g/L, preferably 100 g/L to 130 g/L. Further, the sodium concentration of the nickel solution is preferably 5 mg/L or less, more preferably 1 mg/L or less, and the total concentration of aluminum and manganese is 1 mg/L or less, more preferably 0.5 mg/L or less. .

In the crystallization step, the nickel solution is heated to, for example, 40° C. to 120° C. and concentrated, and nickel ions are crystallized as nickel sulfate.
The nickel sulfate obtained in the crystallization process contains almost no impurities and is suitable for use as a raw material for manufacturing lithium ion batteries.

Next, the above-described method for producing a high-purity cobalt sulfate solution was carried out on a trial basis, and its effects were confirmed, which will be described below. However, the description here is for the purpose of mere illustration, and is not intended to be limiting.

Cobalt sulfate solution of approximately 10 g/L and Ni: 1 g/L was added with bis(2,4,4-trimethylpentyl)phosphinic acid (ALBRITECT TH1) or 2-ethylhexyl 2-ethylhexylphosphinic acid (2,4,4-trimethylpentyl)phosphinic acid (ALBRITECT TH1) as an extractant. PC-88A) and ammonium hydroxide or sodium hydroxide as a pH adjuster, multiple tests were conducted to extract cobalt ions from a cobalt sulfate solution at different pHs.

The Co concentration and Ni concentration in the aqueous phase after extraction (Aq. after extraction) and the organic phase (Org. after extraction) were confirmed. The results are shown in Table 1. 5 to 7 show graphs at each pH, with the horizontal axis representing the Ni concentration in the aqueous phase after extraction and the vertical axis representing the Ni concentration in the organic phase after extraction.

From this result, relatively more Ni was extracted into the solvent when mono-2-ethylhexyl (2-ethylhexyl)phosphinate was used as an extractant, whereas bis(2,4,4-trimethylpentyl) ) It can be seen that when a phosphinic acid extractant was used, the Ni concentration in the solvent was sufficiently low.

Therefore, by using bis(2,4,4-trimethylpentyl)phosphinic acid as an extractant, nickel ions can be separated in the nickel separation process, and the purity of cobalt in the cobalt sulfate solution can be effectively increased. I realized something.

Claims (10)

A method for producing a high-purity cobalt sulfate solution with higher cobalt purity than the cobalt sulfate solution from a cobalt sulfate solution containing nickel ions, the method comprising:
The cobalt/nickel concentration ratio of the cobalt sulfate solution is 100 or more,
The cobalt sulfate solution is brought into contact with a solvent containing bis(2,4,4-trimethylpentyl)phosphinic acid to adjust the pH, and the cobalt ions are transferred to the solvent while leaving the nickel ions in the cobalt sulfate solution in the solution. and a nickel separation step of back-extracting the cobalt ions extracted into the solvent with sulfuric acid,
Before the nickel separation step, a cobalt extraction step is performed in which cobalt ions are extracted from an acidic solution containing cobalt ions and nickel ions into a solvent, and the cobalt ions in the solvent are back-extracted with sulfuric acid to obtain the cobalt sulfate solution. A method for producing a high purity cobalt sulfate solution , further comprising : The method for producing a high-purity cobalt sulfate solution according to claim 1, wherein the high-purity cobalt sulfate solution has a cobalt/nickel concentration ratio of 10,000 or more. Production of a high purity cobalt sulfate solution according to claim 1 or 2, wherein the cobalt concentration of the cobalt sulfate solution is 5 g/L to 90 g/L and the nickel concentration is 0.05 g/L to 0.90 g/L. Method. The method for producing a high-purity cobalt sulfate solution according to any one of claims 1 to 3, wherein in the nickel separation step, the equilibrium pH during extraction is set to 4.0 to 7.0. Further comprising a nickel extraction step of extracting nickel ions into an organic phase from the cobalt extraction residue obtained after extraction of cobalt ions in the cobalt extraction step, and then performing back extraction on the organic phase containing nickel ions. A method for producing a high purity cobalt sulfate solution according to any one of claims 1 to 4. The method for producing a high-purity cobalt sulfate solution according to any one of claims 1 to 5, wherein the cobalt extraction step includes scrubbing a solvent from which cobalt ions have been extracted. Claims 1 to 6, comprising a pretreatment to obtain a battery powder by processing lithium ion battery scrap containing at least cobalt and nickel, and a wet processing to obtain the cobalt sulfate solution by wet processing the battery powder. A method for producing a high purity cobalt sulfate solution according to any one of the items. The method for producing a high-purity cobalt sulfate solution according to claim 7, wherein the pretreatment includes a roasting step, a crushing step, and a sieving step for the lithium ion battery scrap. Sulfuric acid comprising a crystallization step of crystallizing cobalt ions in a high purity cobalt sulfate solution produced by the method for producing a high purity cobalt sulfate solution according to any one of claims 1 to 8 to obtain cobalt sulfate. Cobalt production method. The method for producing cobalt sulfate according to claim 9, wherein cobalt sulfate having a nickel content of 10 mass ppm or less is obtained in the crystallization step.

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