JP2024030548A - Method for producing cobalt hydroxide - Google Patents

Abstract

To provide a method for producing cobalt hydroxide by which the cobalt hydroxide is made from a cobalt chloride liquid as a raw material at a low cost, has good filterability and low chlorine (chloride) grade.SOLUTION: A method for producing cobalt hydroxide comprises adding an alkali to a solution containing chloride and cobalt to produce a slurry and subjecting the slurry to solid-liquid separation. In the method, the solid-liquid separation is characterized in that the pH of the slurry is held in a range of more than 10 and 14 or less for at least 25 minutes, and then the slurry is subjected to solid-liquid separation.SELECTED DRAWING: None

Description

The present invention relates to a method for producing cobalt hydroxide with good filterability and low chlorine grade.

To obtain cobalt compounds such as cobalt oxide used in materials such as secondary batteries, raw materials containing cobalt are leached with acid to obtain a solution, and impurities are removed from this solution using methods such as solvent extraction. A method is known in which a purified liquid is obtained through a purification process, the purified liquid is then neutralized to obtain cobalt hydroxide as an intermediate raw material, and this intermediate raw material is fired, for example, to obtain cobalt oxide.

When processing in the above steps, when the acid used to dissolve the raw material is hydrochloric acid, there is a problem that chlorine (chloride) is mixed in the intermediate raw material obtained by neutralizing the purified liquid.
As one of the methods, when firing is performed, the chloride level is preferably as low as possible because chlorine also damages the material of the firing furnace.
In particular, when cobalt hydroxide is used for battery applications, it is required to reduce the chlorine content in the cobalt hydroxide as much as possible, specifically to 1% by weight or less, in order to maintain properties.

At the same time, since an alkali agent is added to the purified liquid to neutralize it, it is important that the cost of the alkali agent is low. Furthermore, the hydroxide produced by neutralization is generally fine and tends to have low filterability. By the way, if the filtration performance is good, the equipment can be simplified, equipment investment and operational effort can be saved, which is highly effective in reducing costs.
Furthermore, if the filterability is poor, chlorine (chloride) will adhere around the cobalt hydroxide, which will increase the chlorine quality of the cobalt hydroxide, which is undesirable as it may affect the battery characteristics as described above.
In other words, cobalt hydroxide with good filterability and low impurity concentration is required.

As a method for producing cobalt hydroxide from a cobalt chloride solution, for example, Patent Document 1 describes a method for neutralizing the cobalt chloride solution by adding an alkali such as sodium hydroxide to adjust the pH to 8.0 to 9.5. A method for obtaining cobalt hydroxide is disclosed.

However, when a cobalt chloride solution is neutralized by the above method, there are problems in that the resulting cobalt hydroxide contains high chlorine (chloride) quality and has poor filtration performance during solid-liquid separation.

As mentioned above, cobalt hydroxide with a high chlorine content is not suitable for use as a material for batteries, and poor filtration performance leads to a decrease in productivity and an increase in operating costs, both of which are undesirable.

Furthermore, Patent Document 2 states that when neutralizing a cobalt chloride solution by adding an alkali, the pH is first controlled in the range of 10.5 to 12.0 to generate particles that will become the core of cobalt hydroxide crystals. A method is disclosed in which particles are grown by lowering the pH to a range of 9.5 to 10.5 and adding a complexing agent. It has the characteristic that filterability can be expected to improve due to the growth of particles.

However, the above method uses ammonia as a complexing agent, and when disposing of the solution after cobalt recovery by subjecting it to wastewater treatment, denitrification treatment is required to remove nitrogen from the wastewater, which is time-consuming and time-consuming. There are costly issues.

Furthermore, since the chlorine concentration decreases with the second stage pH adjustment, there is also the problem that the chlorine grade in the cobalt hydroxide increases.
As described above, it has not been easy to improve the quality and productivity of cobalt hydroxide, which is an intermediate raw material for battery materials.

Japanese Unexamined Patent Publication No. 60-195024 Japanese Patent Application Publication No. 2015-165477

In order to solve this situation, the purpose of the present invention is to produce cobalt hydroxide using cobalt chloride liquid as a raw material, which is inexpensive, has good filterability, and can lower the chlorine (chloride) grade. The purpose is to provide a method.

The present inventors used a chlorine-containing cobalt salt solution as a raw material, added an alkaline agent later, and maintained the pH for 25 minutes or more from the time when the pH reached 10.5 or higher while stirring, thereby reducing the chlorine level. It was discovered that cobalt hydroxide with good filterability can be obtained at 1% or less, and the present invention was completed.

That is, the first aspect of the present invention is a method for producing cobalt hydroxide by adding an alkali to a solution containing chloride and cobalt, and separating the slurry into solid-liquid to obtain cobalt hydroxide. is a method for producing cobalt hydroxide, which comprises maintaining the pH of the slurry in a range of more than 10 and less than or equal to 14 for 25 minutes or more, and then subjecting the slurry to solid-liquid separation.

By using the method for producing cobalt hydroxide of the present invention, cobalt hydroxide with good filterability and low chlorine content can be obtained.

This is an electron micrograph showing the change in particle size due to retention time when the pH was set to 11.2, without retention. This is an electron micrograph showing the change in particle size depending on the holding time when the pH was set to 11.2, and the sample was held for 25 minutes. This is an electron micrograph showing the change in particle size depending on the holding time when the pH was set to 11.2 and the sample was held for 50 minutes. This is an electron micrograph showing the change in particle size depending on the holding time when the pH was set to 11.2 and the sample was held for 75 minutes. It is an electron micrograph showing the change in particle size when the pH was set to 8.0 when the holding time was set to 75 minutes. There is an electron micrograph showing the change in particle size when the pH was set to 10.0 when the holding time was 75 minutes. It is an electron micrograph showing the change in particle size at pH 11.2 when the holding time was 75 minutes. It is an electron micrograph showing the change in particle size at pH 12.0 when the holding time was 75 minutes.

Hereinafter, the method for producing cobalt hydroxide of the present invention will be explained in detail.
The method for producing cobalt hydroxide of the present invention is characterized by using a chlorine-containing cobalt salt solution as a raw material, adding an alkali agent later, and maintaining it for 25 minutes or more when the pH exceeds 10 while stirring, Cobalt hydroxide with a chlorine content of 1% or less and good filterability can be obtained.
Furthermore, since the present invention does not use a complexing agent, the effort and cost of wastewater treatment can be reduced, and it is also environmentally friendly.
In the present invention, crystals are grown by increasing the pH to produce cobalt hydroxide with low chlorine concentration and good filterability.

When sodium hydroxide is added to neutralize a cobalt chloride solution, a fine mixture of _Co2Cl (OH) ₃ and Co(OH) ₂ is formed at first, and then _Co2Cl (OH) is formed over time. It was found that ₃ was converted to Co(OH) ₂ .
In other words, even if neutralization is carried out to a predetermined pH, the morphology will change and the particle size will become coarser as shown in Figures 1a to 1d, and the resulting cobalt compound particles will get caught up in the particles themselves or in the gaps between the particles. chlorine content can be reduced.

Furthermore, as shown in FIGS. 2a to 2d, even if the holding time is the same, cobalt hydroxide with a larger particle size is obtained when the pH is higher, and the chlorine grade also tends to decrease.
Therefore, by raising the pH to a value higher than 10 and having a holding time of 25 minutes or more before starting filtration after pH adjustment, only one stage of pH adjustment is required, unlike conventional methods, and ammonia, etc. Cobalt hydroxide with low chlorine concentration and good filterability can be obtained without using a complexing agent.

Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples.
A cobalt chloride solution with a cobalt concentration of 76 g/L was used as a raw material. The pH of the solution was 2.5. Note that the raw material is not limited to a cobalt chloride solution, and an acidic cobalt-containing solution such as a cobalt sulfate solution can be similarly treated.
As the alkaline agent, a sodium hydroxide solution with a concentration of 8 mol/L manufactured by Fuji Film Wako Pure Chemical Industries, Ltd. was used. Other alkaline agents that can be used include magnesium hydroxide, calcium hydroxide, calcium oxide, sodium carbonate, or mixtures thereof.

A glass reaction vessel with a capacity of 500 ml was placed in a water bath, and the temperature of the cobalt chloride solution was maintained at a constant temperature of 60°C. The liquid temperature can also be varied from room temperature to about 95°C. Note that a PVC lid was provided on the top of the reaction container. The lid was provided with an alkali agent inlet, a nitrogen gas inlet, and a pH electrode inlet.

During the reaction, pH was continuously measured. A model HM41X manufactured by Toa DKK Co., Ltd. was used as a measuring device, and a model GST-5841C manufactured by Toa DKK Co., Ltd., which uses a silver-silver chloride electrode as a reference electrode, was used as a pH electrode. As a metering pump for adding the alkali agent, model SMP-21 manufactured by Tokyo Rikakikai Co., Ltd. was used.

As a specific procedure, first, 200 ml of cobalt chloride solution was charged into the reaction container, and a sodium hydroxide solution with a concentration of 8 mol/L was added using a liquid pump at a flow rate of 2 ml/min until the pH reached each set value. At the same time, nitrogen gas supplied from a cylinder was blown into the slurry in the reaction tank through a sinter glass at a flow rate of 1 L/min.

After reaching the set value, the set time was maintained from 0 minutes to 75 minutes while adjusting the flow rate so as to maintain the set pH, and after reaching the set time, filtration was performed to separate the filtrate and the filtrate.
Note that when the holding time was 0 minutes, filtration was started immediately after reaching the set pH.

After the test was completed, filtration was performed using a Nutsche filter. As the filter paper, a 125 mm diameter 5C filter paper (particle retention capacity 1 μm) manufactured by Advantech was used. The dry vacuum pump used was a model DTC-41 manufactured by ULVAC Kiko Co., Ltd. The filtration time was determined from the time when the slurry was added to Nutsche until cracks appeared in the filtrate cake by visual observation.

Note that the shorter the filtration time, the better; however, in general, if the amount of slurry is approximately the same, 300 seconds or less is preferable. After the filtration was completed, 300 ml of pure water was passed through the filter 4 times to wash the filtrate cake to obtain a washed filtrate.

Next, the washed filtrate was placed in a vacuum dryer and dried for 12 hours to obtain a dried filtrate, and the components of the dried filtrate were then analyzed. Note that a commercially available X-ray fluorescence analyzer (XRF) was used to analyze the chlorine (chloride) concentration.

(Example 1 to Example 9)
Under the conditions shown in Table 1 (“set pH”, “retention time [min]”, chlorine grade [%]), after the cobalt hydroxide production test according to Examples 1 to 9 according to the present invention, solidification by filtration was performed. Liquid separation was performed, and the "filtration time [sec]" was measured, and the results are listed in Table 1 together with the above conditions.

(Comparative Example 1 to Comparative Example 11)
After the cobalt hydroxide production test according to Comparative Examples 1 to 11 of the present invention under the conditions shown in Table 1 (“set pH”, “holding time [min]”, chlorine grade [%]), solidification by filtration was performed. Liquid separation was performed, the "filtration time [sec]" was measured, and the results are listed in Table 1 together with the above conditions.

[Consideration]
In Examples 1 to 9, the set pH was set to "10.5, 11.2, 12.0" within the scope of the present invention, and the holding time was set to "25 minutes or more", as shown in Table 1. In addition, results were obtained in which the chloride level was low and the filtration time was short (that is, the filtration rate was fast).
On the other hand, in Comparative Examples 4 to 11, in which the set pH was set to "8.0" and "10.0" outside the range of the present invention, the targets could not be achieved in both the time required for filtration and the chlorine quality.
In addition, in Comparative Examples 1 to 3 (no holding time) where the holding time was less than 25 minutes, the set pH was satisfied, but the time required for filtration was too long, and the chlorine quality could not achieve the target. .

As described above, it was found that cobalt hydroxide with good filterability and a chlorine content of less than 1% can be obtained by setting the pH to over 10.0 and the holding time to 25 minutes or more.

Claims (1)

A method of producing a slurry by adding an alkali to a solution containing chloride and cobalt, and separating the slurry into solid-liquid to obtain cobalt hydroxide,
A method for producing cobalt hydroxide, wherein the solid-liquid separation is performed by maintaining the pH of the slurry in a range of more than 10 and 14 or less for 25 minutes or more, and then subjecting the slurry to solid-liquid separation.