JPH11315391A - Method for refining cobalt - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for obtaining cobalt of extremely high purity (higher than 5N level) suitable for use for a target or the like. SOLUTION: This electrolytic refining method is the one in which crude cobalt metal is used as an anode, an aq. soln. of cobalt sulfate is used as an electrolytic soln., the electrolytic conditions are controlled to pH: 1 to 3, cobalt concn.: 40 to 160 g/l and cathode current density: 0.01 to 0.1 A/cm<2> , and the refined cobalt metal is electrodeposited on a cathode board. The concns. of nickel and iron in the electrodeposited cobalt are reduced to 1 ppm, particularly to <=0.5 ppm. Preferably, the average concn. of nickel in the aq. soln. of cobalt is controlled to <=1.3 mg/l, and the average concn. of iron is controlled to <=0.1 mg/l.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for electrolytically refining an aqueous solution of cobalt, and more particularly to a method for producing high purity cobalt of 5N or more which is important as a cobalt sputtering target material for manufacturing semiconductor devices. The present invention relates to an electrolytic refining method and a high-purity cobalt sputtering target for manufacturing semiconductor devices. The high-purity cobalt purified according to the present invention has a metal impurity harmful to semiconductor devices, particularly iron and nickel, reduced to 1 ppm or less, particularly 0.5 ppm or less. It is suitable as.

[0002]

2. Description of the Related Art A sputtering target is a generally disk-shaped plate that serves as a sputtering source for forming electrodes, gates, wirings, elements, protective films and the like of various semiconductor devices on a substrate by sputtering. When the accelerated particles collide with the target surface, the atoms constituting the target are released into space by the exchange of momentum and are deposited on the opposing substrate. As the sputtering target, an Al alloy target, a refractory metal and alloy target, a silicide target, and the like are typically used. Among these, one of the highly useful targets is a cobalt and cobalt alloy target.

It is important that a semiconductor device member formed after sputtering contains a minimum of harmful metallic impurities in the semiconductor device in order to guarantee reliable semiconductor operation performance. Such a cobalt-based target is generally produced by powder metallurgy of a cobalt powder, that is, by sintering after cold pressing or hot pressing. Therefore, in order to ensure the purity of the cobalt target, a high level of the target raw material itself is required. Purification is essential.

[0004] Commonly available cobalt, the so-called crude cobalt mass, contains as impurities tens of ppm of iron and hundreds of ppm of nickel. As a method for producing high-purity cobalt, low-purity cobalt is electrochemically dissolved, impurities in an aqueous cobalt solution are removed using an ion-exchange method, the solution is concentrated, and high-purity electrolytic cobalt is collected by electrolytic extraction. Is a method of producing Bourahl
a, Acad. Sci, Ser, C.I. 278 (10) 6
79-680 (1974). But,
This method has a problem that it is of a batch type, is therefore suitable for small-quantity production, has many steps, and is expensive.

[0005] Electrowinning is a method in which a solution containing a target metal is used as an electrolytic solution, and an electrolytic solution is electrolyzed using an insoluble anode to deposit the target metal on a cathode. Therefore, for example, in the method of electrolytically collecting cobalt from an aqueous solution of cobalt sulfate, an overvoltage for generating oxygen gas at the anode is required, and an electrolytic purification method in which the target metal is electrolyzed as a soluble anode to deposit the target metal on the cathode, and In addition to the above-mentioned problems, there were various problems other than the above-mentioned problems, such as the increase of the cell voltage by about 2 V and the necessity of adjusting the cobalt concentration and the pH.

On the other hand, although the electrolytic refining method can be considered, it is said that it is difficult to achieve high purity by the electrolytic refining method because the standard electrode potentials of nickel, iron and cobalt as impurities are very close. It has been said that there has been little consideration until now.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a 5N (99.999%, hereinafter simply referred to as 5N) which contains only a minimum of impurities such as nickel and iron suitable for applications such as a target.
To develop a method for purifying cobalt at a high level or higher.

[0008]

Means for Solving the Problems The present inventors have conducted intensive studies so as to stably produce a large amount of high-purity cobalt. The inventors have found that the metal can be purified due to a difference in overvoltage, and that the purification rate also largely depends on the impurity concentration in the aqueous solution. In other words, the standard electrode potentials of nickel and iron and cobalt, which are impurities, are very close to each other, and it is difficult to perform electrolytic refining. It has been found that by limiting, electrodeposition of cobalt is possible while avoiding precipitation of iron and nickel.

Based on this finding, the present invention provides (1) a method of depositing purified cobalt metal on a cathode plate using a crude cobalt metal as an anode and an aqueous solution of cobalt sulfate as an electrolyte, and adjusting the pH of the electrolyte to 1 to 3. Electrolysis of cobalt to produce 5N or more cobalt, characterized in that the electrolyte has a cobalt concentration of 40 to 160 g / l and a cathode current density of 0.001 to 0.1 A / cm ^2. It provides a purification method. It was also found that the purification rate greatly depends on the impurity concentration in the aqueous cobalt sulfate solution. Therefore, the present invention further provides (2) an average nickel impurity concentration of 1.3 mg in the aqueous cobalt sulfate solution.
/ L or less, and the average concentration of impurity iron is 0.1 mg.
/ L or less, wherein the method for electrolytically refining cobalt according to (1) and the method for reducing (3) impurity nickel and iron are solvent extraction or ion exchange. The present invention also provides a method for electrolytically refining cobalt according to the above (2). The present invention further provides (4) a high-purity cobalt sputtering target for manufacturing a semiconductor device, wherein (4) a purity of 5 N or more and iron and nickel as impurities are 1 ppm or less, and (5) a purity of 5 N.
As described above, the present invention provides a high-purity cobalt sputtering target for manufacturing a semiconductor device, wherein iron and nickel as impurities are 0.5 ppm or less. In the present invention, the average density means an average value of the sum of the initial density and the end density.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The electrolytic solution used in the present invention is an aqueous solution of cobalt sulfate which has been acidified with sulfuric acid. The optimum cobalt concentration in the electrolyte is generally between 40 and 160 g / l,
More preferably, it is 70 to 130 g / l. 40g /
If it is less than 1, the amount of generated hydrogen is increased, so that the current efficiency is extremely deteriorated, and the impurity concentration in the deposited cobalt is undesirably increased. If it exceeds 160 g / l, it is not preferable because cobalt sulfate precipitates and adversely affects the electrodeposition state.

The optimum pH range of the electrolyte is generally 1 to 3.
And more preferably 1.5 to 2.5. pH1
If it is less than 1, the amount of generated hydrogen is increased, and the current efficiency is extremely lowered. If the pH exceeds 3, the content of impurities, especially nickel, in the deposited cobalt increases rapidly, which is not preferable.

The optimum cathode current density range is 0.001.
０．１0.1 A / cm ² . If it is less than 0.001 A / cm ² , the productivity will be reduced and it will not be efficient. On the other hand, 0.
If it exceeds 1 A / cm ² , the impurity concentration in the deposited cobalt increases, and the current efficiency also decreases, which is not preferable.

[0013] The electrolysis temperature is preferably in the range of 10 to 65 ° C, more preferably 35 to 55 ° C. If the temperature is lower than 10 ° C., the current efficiency decreases, which is not preferable. When the temperature exceeds 65 ° C., evaporation of the electrolytic solution increases, and the cobalt concentration in the electrolytic solution fluctuates and cobalt sulfate is undesirably deposited.

It has been found that the impurity concentration in the electrolytic solution used under the above-mentioned electrolysis conditions has an unexpectedly strong influence on the impurity content in the deposited cobalt. 1 and 2 are graphs respectively showing the relationship between the nickel and iron concentrations in the initial electrolyte and the nickel and iron concentrations in the deposited cobalt.

When a relational expression between the nickel concentration in the liquid and the nickel content in the deposited cobalt was determined, Y = 0.78X
It was found that From this, to achieve 5N or more, the nickel content in the deposited cobalt should be 1 ppm.
The initial nickel concentration in the solution was 1.3 mg
/ L or less, that is, 1.3 mg / l even at the average concentration.
It turns out that you have to:

It has been found that iron is expressed by Y = 10X similarly. This shows that in order to reduce the iron concentration to 1 ppm or less, the initial concentration in the solution must be 0.1 mg / l or less, that is, the average concentration must be 0.1 mg / l or less.

Such reduction of impurities such as nickel and iron can be achieved by using a solvent extraction method, an ion exchange method or the like.

As the cobalt source, a commercially available electrodeposited cobalt lump or scrap can be used. They usually contain 10-30 pm of iron and 100-500 ppm of nickel. For the electrolysis, it is preferable to employ a diaphragm electrolysis in which an anode box (anolyte) and a cathode box (catholyte) are separated by a diaphragm in order to prevent contamination with impurities. It is convenient to place the cobalt source in a suitable meshed container and charge the anode box. As the material of the cathode base plate, a cobalt, titanium plate, or the like is used. The container for electrolytic refining is made of vinyl chloride, polypropylene, polyethylene or the like.

The deposited cobalt produced under the above electrolytic conditions contains impurities, particularly nickel and iron, of 1 pp.
m, especially 0.5 ppm or less, which is particularly preferable as a sputtering target material for a semiconductor device.

[0020]

EXAMPLES Examples and comparative examples of the present invention will be described below.

(Example 1) 2 kg of a crude cobalt lump having a purity as shown in Table 1 was charged into an anode box of an electrolytic cell containing about 100 liters of a sulfuric acid aqueous solution. As the cathode plate (base plate), a 2 mm-thick cobalt plate was used. The initial nickel and iron concentrations in the electrolyte were 0.01 mg
/ L (less than or equal to the lower limit of analysis). The electrolysis conditions were as follows: (1) pH: 2, (2) cobalt concentration in electrolyte: 100 g / l, (3) cathode current density: 0.02 A / cm ² , (4) temperature: 50 ° C., (5) electrolysis Time: 40 hr (6) Electrodeposition: 870 g At this time, the average nickel concentration in the liquid was 0.8 mg / l and the average iron concentration was 0.1 mg / l (average concentration = average value of the sum of the initial concentration and the end concentration).

Table 1 shows the impurity content and the yield in the thus obtained electrodeposited cobalt. Nickel content is 0.5
ppm and the iron content was reduced to 0.4 ppm. The yield is also at the level of 98%.

Example 2 Using the same apparatus as in Example 1, cobalt electrolytic purification was performed. The electrolysis conditions include (1) pH: 2.5, (2) cobalt concentration in the electrolyte: 50 g / l, (3) cathode current density: 0.005 A / cm ² (4) temperature: 20 ° C., (5) ) Electrolysis time: 40 hr (6) Electrodeposition amount: 875 g The average nickel concentration in the liquid is 0.8mg
/ L and the average iron concentration was 0.1 mg / l.

Table 1 shows the impurity content and the yield in the cobalt deposit thus obtained. Nickel content is 0.5
ppm and the iron content was reduced to 0.5 ppm. The yield is also maintained at a level of 90%.

(Comparative Example 1) Using the same apparatus as in Example 1, cobalt electrolytic purification was performed. The electrolysis conditions are as follows: (1) pH: 4.0, (2) Cobalt concentration in electrolyte: 100 g / l (3) Cathode current density: 0.02 A / cm ² (4) Temperature: 50 ° C., (5) Electrolysis time: 40 hr (6) Electrodeposition amount: 870 g pH is higher than specified in the present invention. The average nickel concentration in the solution was 0.8 mg / l and the average iron concentration was 0.1 mg / l.

Table 1 shows the impurity content and the yield in the cobalt deposit thus obtained. It can be seen that the Ni concentration is as high as 70 ppm.

(Comparative Example 2) Using the same apparatus as in Example 1, cobalt electrolytic purification was performed. The electrolysis conditions are as follows: (1) pH: 4.0, (2) Cobalt concentration in electrolyte: 100 g / l (3) Cathode current density: 0.2 A / cm ² (4) Temperature: 50 ° C., (5) Electrolysis time: 40 hr (6) Electrodeposition amount: 520 g The pH and cathode current density are higher than the conditions specified by the present invention. The average nickel concentration in the solution was 0.1.
It was 8 mg / l and the average iron concentration was 0.1 mg / l.

Table 1 shows the content and yield of impurities in the cobalt deposit thus obtained. Nickel content is 100
ppm and the iron content was 10 ppm. The yield is as low as 70%.

(Comparative Example 3) Using the same apparatus as in Example 1, cobalt electrolytic purification was performed. The electrolysis conditions are as follows: (1) pH: 2.0, (2) Cobalt concentration in electrolyte: 10 g / l (3) Cathode current density: 0.02 A / cm ² (4) Temperature: 50 ° C., (5) Electrolysis time: 40 hr (6) Electrodeposition amount: 610 g The cobalt concentration in the electrolyte is lower than the range specified in the present invention. The average nickel concentration in the solution is 0.8 mg /
and the average iron concentration was 0.1 mg / l on average.

Table 1 shows the impurity content and the yield in the thus obtained electrodeposited cobalt. Nickel content is 200
ppm and the iron content was 10 ppm. The yield is also low.

[0031]

[Table 1]

[0032]

According to the present invention, high purity cobalt of 5N or more, particularly reduced nickel and iron, can be easily obtained by electrolytic refining, and the obtained high purity cobalt is suitable as a target material for semiconductor device production. is there.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the initial nickel impurity concentration in an electrolytic solution and the nickel content in electrodeposited cobalt.

FIG. 2 is a graph showing a relationship between an initial impurity concentration in an electrolytic solution and an iron content in electrodeposited cobalt.

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[Procedure amendment]

[Submission date] March 19, 1999

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction contents]

[Document Name] Statement

[Title of the Invention] Cobalt purification method

[Claims]

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for electrolytically refining an aqueous solution of cobalt, and more particularly to a method for producing high purity cobalt of 5N or more which is important as a cobalt sputtering target material for manufacturing semiconductor devices. about the electrolytic refining how. The high-purity cobalt purified according to the present invention contains metal impurities harmful to semiconductor devices, particularly iron and nickel, of 1 ppm or less, particularly 0.5 ppm.
It is reduced as follows, and is suitable as a cobalt sputtering target material or the like for manufacturing semiconductor devices.

[0002]

2. Description of the Related Art A sputtering target is a generally disk-shaped plate that serves as a sputtering source for forming electrodes, gates, wirings, elements, protective films and the like of various semiconductor devices on a substrate by sputtering. When the accelerated particles collide with the target surface, the atoms constituting the target are released into space by the exchange of momentum and are deposited on the opposing substrate. As the sputtering target, an Al alloy target, a refractory metal and alloy target, a silicide target, and the like are typically used. Among these, one of the highly useful targets is a cobalt and cobalt alloy target.

It is important that a semiconductor device member formed after sputtering contains a minimum of harmful metallic impurities in the semiconductor device in order to guarantee reliable semiconductor operation performance. Such a cobalt-based target is generally produced by powder metallurgy of a cobalt powder, that is, by sintering after cold pressing or hot pressing. Therefore, in order to ensure the purity of the cobalt target, a high level of the target raw material itself is required. Purification is essential.

[0004] Commonly available cobalt, the so-called crude cobalt mass, contains as impurities tens of ppm of iron and hundreds of ppm of nickel. As a method for producing high-purity cobalt, low-purity cobalt is electrochemically dissolved, impurities in an aqueous cobalt solution are removed using an ion-exchange method, the solution is concentrated, and high-purity electrolytic cobalt is collected by electrolytic extraction. Is a method of producing Bourahl
a, Acad. Sci, Ser, C.I. 278 (10) 6
79-680 (1974). But,
This method has a problem that it is of a batch type, is therefore suitable for small-quantity production, has many steps, and is expensive.

[0005] Electrowinning is a method in which a solution containing a target metal is used as an electrolytic solution, and an electrolytic solution is electrolyzed using an insoluble anode to deposit the target metal on a cathode. Therefore, for example, in the method of electrolytically collecting cobalt from an aqueous solution of cobalt sulfate, an overvoltage for generating oxygen gas at the anode is required, and an electrolytic purification method in which the target metal is electrolyzed as a soluble anode to deposit the target metal on the cathode, and In addition to the above-mentioned problems, there were various problems other than the above-mentioned problems, such as the increase of the cell voltage by about 2 V and the necessity of adjusting the cobalt concentration and the pH.

On the other hand, although the electrolytic refining method can be considered, it is said that it is difficult to achieve high purity by the electrolytic refining method because the standard electrode potentials of nickel, iron and cobalt as impurities are very close. It has been said that there has been little consideration until now.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a 5N (99.999%, hereinafter simply referred to as 5N) which contains only a minimum of impurities such as nickel and iron suitable for applications such as a target.
To develop a method for purifying cobalt at a high level or higher.

[0008]

Means for Solving the Problems The present inventors have conducted intensive studies so as to stably produce a large amount of high-purity cobalt. The inventors have found that the metal can be purified due to a difference in overvoltage, and that the purification rate also largely depends on the impurity concentration in the aqueous solution. In other words, the standard electrode potentials of nickel and iron and cobalt, which are impurities, are very close to each other, and it is difficult to perform electrolytic refining. It has been found that by limiting, electrodeposition of cobalt is possible while avoiding precipitation of iron and nickel.

Based on this finding, the present invention provides:
Cobalt metal anode and cobalt sulfate aqueous solution
Of purified cobalt metal on the cathode plate by using
The pH of the electrolyte solution to 1 to 3
Filter concentration is 40-160 g / l and the cathode current density
The degree is 0.001-0.1 A / cm^Two That the conditions of
Kobal for producing 5N or more of cobalt
To provide a method for electrolytic purification of The purification rate is
Dependence on impurity concentration in aqueous cobaltate solution
Also turned out. Therefore, the present invention further provides (2)
The average concentration of the nickel impurities in the aqueous solution is 1.3 mg.
/ L or less, and the average concentration of impurity iron is 0.1 mg.
/ L or less.
Baltic electrolytic purification method and (3) impurity nickel and
Solvent extraction method or ion exchange method to reduce pure iron
The cobalt according to the above (2),
An electrolytic purification method is also provided. In the present invention, the average darkness
Degree means the average value of the sum of the initial density and the end density.
To taste.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The electrolytic solution used in the present invention is an aqueous solution of cobalt sulfate which has been acidified with sulfuric acid. The optimum cobalt concentration in the electrolyte is generally between 40 and 160 g / l,
More preferably, it is 70 to 130 g / l. 40g /
If it is less than 1, the amount of generated hydrogen is increased, so that the current efficiency is extremely deteriorated, and the impurity concentration in the deposited cobalt is undesirably increased. If it exceeds 160 g / l, it is not preferable because cobalt sulfate precipitates and adversely affects the electrodeposition state.

The optimum pH range of the electrolyte is generally 1 to 3.
And more preferably 1.5 to 2.5. pH1
If it is less than 1, the amount of generated hydrogen is increased, and the current efficiency is extremely lowered. If the pH exceeds 3, the content of impurities, especially nickel, in the deposited cobalt increases rapidly, which is not preferable.

The optimum cathode current density range is 0.001.
０．１0.1 A / cm ² . If it is less than 0.001 A / cm ² , the productivity will be reduced and it will not be efficient. On the other hand, 0.
If it exceeds 1 A / cm ² , the impurity concentration in the deposited cobalt increases, and the current efficiency also decreases, which is not preferable.

[0013] The electrolysis temperature is preferably in the range of 10 to 65 ° C, more preferably 35 to 55 ° C. If the temperature is lower than 10 ° C., the current efficiency decreases, which is not preferable. When the temperature exceeds 65 ° C., evaporation of the electrolytic solution increases, and the cobalt concentration in the electrolytic solution fluctuates and cobalt sulfate is undesirably deposited.

It has been found that the impurity concentration in the electrolytic solution used under the above-mentioned electrolysis conditions has an unexpectedly strong influence on the impurity content in the deposited cobalt. 1 and 2 are graphs respectively showing the relationship between the nickel and iron concentrations in the initial electrolyte and the nickel and iron concentrations in the deposited cobalt.

When a relational expression between the nickel concentration in the liquid and the nickel content in the deposited cobalt was determined, Y = 0.78X
It was found that From this, to achieve 5N or more, the nickel content in the deposited cobalt should be 1 ppm.
The initial nickel concentration in the solution was 1.3 mg
/ L or less, that is, 1.3 mg / l even at the average concentration.
It turns out that you have to:

It has been found that iron is expressed by Y = 10X similarly. This shows that in order to reduce the iron concentration to 1 ppm or less, the initial concentration in the solution must be 0.1 mg / l or less, that is, the average concentration must be 0.1 mg / l or less.

Such reduction of impurities such as nickel and iron can be achieved by using a solvent extraction method, an ion exchange method or the like.

As the cobalt source, a commercially available electrodeposited cobalt lump or scrap can be used. They usually contain 10-30 pm of iron and 100-500 ppm of nickel. For the electrolysis, it is preferable to employ a diaphragm electrolysis in which an anode box (anolyte) and a cathode box (catholyte) are separated by a diaphragm in order to prevent contamination with impurities. It is convenient to place the cobalt source in a suitable meshed container and charge the anode box. As the material of the cathode base plate, a cobalt, titanium plate, or the like is used. The container for electrolytic refining is made of vinyl chloride, polypropylene, polyethylene or the like.

The deposited cobalt produced under the above electrolytic conditions contains impurities, particularly nickel and iron, of 1 pp.
m, especially 0.5 ppm or less, which is particularly preferable as a sputtering target material for a semiconductor device.

[0020]

EXAMPLES Examples and comparative examples of the present invention will be described below.

(Example 1) 2 kg of a crude cobalt lump having a purity as shown in Table 1 was charged into an anode box of an electrolytic cell containing about 100 liters of a sulfuric acid aqueous solution. As the cathode plate (base plate), a 2 mm-thick cobalt plate was used. The initial nickel and iron concentrations in the electrolyte were 0.01 mg
/ L (less than or equal to the lower limit of analysis). The electrolysis conditions were as follows: (1) pH: 2, (2) cobalt concentration in electrolyte: 100 g / l, (3) cathode current density: 0.02 A / cm ² , (4) temperature: 50 ° C., (5) electrolysis Time: 40 hr (6) Electrodeposition: 870 g At this time, the average nickel concentration in the liquid was 0.8 mg / l and the average iron concentration was 0.1 mg / l (average concentration = average value of the sum of the initial concentration and the end concentration).

Table 1 shows the impurity content and the yield in the thus obtained electrodeposited cobalt. Nickel content is 0.5
ppm and the iron content was reduced to 0.4 ppm. The yield is also at the level of 98%.

Example 2 Using the same apparatus as in Example 1, cobalt electrolytic purification was performed. The electrolysis conditions include (1) pH: 2.5, (2) cobalt concentration in the electrolyte: 50 g / l, (3) cathode current density: 0.005 A / cm ² (4) temperature: 20 ° C., (5) ) Electrolysis time: 40 hr (6) Electrodeposition amount: 875 g The average nickel concentration in the liquid is 0.8mg
/ L and the average iron concentration was 0.1 mg / l.

Table 1 shows the impurity content and the yield in the cobalt deposit thus obtained. Nickel content is 0.5
ppm and the iron content was reduced to 0.5 ppm. The yield is also maintained at a level of 90%.

(Comparative Example 1) Using the same apparatus as in Example 1, cobalt electrolytic purification was performed. The electrolysis conditions are as follows: (1) pH: 4.0, (2) Cobalt concentration in electrolyte: 100 g / l (3) Cathode current density: 0.02 A / cm ² (4) Temperature: 50 ° C., (5) Electrolysis time: 40 hr (6) Electrodeposition amount: 870 g pH is higher than specified in the present invention. The average nickel concentration in the solution was 0.8 mg / l and the average iron concentration was 0.1 mg / l.

Table 1 shows the impurity content and the yield in the cobalt deposit thus obtained. It can be seen that the Ni concentration is as high as 70 ppm.

(Comparative Example 2) Using the same apparatus as in Example 1, cobalt electrolytic purification was performed. The electrolysis conditions are as follows: (1) pH: 4.0, (2) Cobalt concentration in electrolyte: 100 g / l (3) Cathode current density: 0.2 A / cm ² (4) Temperature: 50 ° C., (5) Electrolysis time: 40 hr (6) Electrodeposition amount: 520 g The pH and cathode current density are higher than the conditions specified by the present invention. The average nickel concentration in the solution was 0.1.
It was 8 mg / l and the average iron concentration was 0.1 mg / l.

Table 1 shows the content and yield of impurities in the cobalt deposit thus obtained. Nickel content is 100
ppm and the iron content was 10 ppm. The yield is as low as 70%.

(Comparative Example 3) Using the same apparatus as in Example 1, cobalt electrolytic purification was performed. The electrolysis conditions are as follows: (1) pH: 2.0, (2) Cobalt concentration in electrolyte: 10 g / l (3) Cathode current density: 0.02 A / cm ² (4) Temperature: 50 ° C., (5) Electrolysis time: 40 hr (6) Electrodeposition amount: 610 g The cobalt concentration in the electrolyte is lower than the range specified in the present invention. The average nickel concentration in the solution is 0.8 mg /
and the average iron concentration was 0.1 mg / l on average.

Table 1 shows the impurity content and the yield in the thus obtained electrodeposited cobalt. Nickel content is 200
ppm and the iron content was 10 ppm. The yield is also low.

[0031]

[Table 1]

[0032]

According to the present invention, high purity cobalt of 5N or more, particularly reduced nickel and iron, can be easily obtained by electrolytic refining, and the obtained high purity cobalt is suitable as a target material for semiconductor device production. is there.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the initial nickel impurity concentration in an electrolytic solution and the nickel content in electrodeposited cobalt.

FIG. 2 is a graph showing a relationship between an initial impurity concentration in an electrolytic solution and an iron content in electrodeposited cobalt.

Claims (3)

[Claims] 1. A method for depositing purified cobalt metal on a cathode plate using a crude cobalt metal as an anode and an aqueous solution of cobalt sulfate as an electrolyte, the pH of the electrolyte is 1 to
3. Electrolysis of cobalt to produce 5N or more cobalt, characterized in that the electrolyte has a cobalt concentration of 40 to 160 g / l and a cathode current density of 0.001 to 0.1 A / cm ^2. Purification method. 2. The method according to claim 1, wherein the average concentration of the impurity nickel in the aqueous cobalt sulfate solution is 1.3 mg / l or less, and the average concentration of the impurity iron is 0.1 mg / l or less. Electrolytic purification of cobalt. 3. The method for electrolytically refining cobalt according to claim 2, wherein the method for reducing the nickel and iron impurities is a solvent extraction method or an ion exchange method.