JP2000144473A - Electrolytic refining method for copper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obviate the generation of wrinkles and blobs in electric copper, to eliminate the need for providing a power interruption time at the time of resetting to a positive pole and to improve productivity by specifying the energization time of the inversion current and the energization time of the positive current in electrolytic refining. SOLUTION: In electrolytic refining of copper using a periodic inversion current, the energization time of the inversion current is set at >=60 seconds/ times and the energization time of the positive current is regulated to 1,200 to 3,000 seconds/times. An electrolytic concentration gradient of an electrolyte nonuniformly formed near the electrode surface at the time of energization of the positive current is negated by keeping the inversion current supplied for >=60 seconds, by which the electrolyte concentration is made uniform and the preferential elution of the copper from the projecting parts of the cathode surface is progressed and the flat surface shape is reset. The inversion current density is preferably set at 0.5 to 1.0 times the positive current density. As a result, even if the electrolysis is operated at the high current density, the electric copper may be produced without degrading the appearance quality. The amount of the additive for smoothing cathode deposition may be decreased.

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 copper, and more particularly to a method for periodically reversing a current.
urrent) to electrolytically purify copper. In the following, “periodic inversion” is abbreviated as “PR” as appropriate.

[0002]

2. Description of the Related Art In the process of electrorefining nonferrous metals such as copper,
High current density operation is aimed at improving productivity. In a normal DC electrolysis method, when the current density is increased to about 300 A / m ² or more, passivation occurs on the anode side and elution is suppressed, and deposition on the cathode becomes uneven, resulting in electrolytic copper (electrodeposited product) Since defects such as wrinkles and bumps are generated on the surface and impurities are trapped and copper quality is reduced,
The current density that can be used industrially is limited to about 300 A / m ² . On the other hand, according to the PR electrolysis method, it is said that passivation on the anode side can be prevented, and it is possible to perform electrolysis at a much higher current density. Attempts have been made to perform current density operations. In general, the current reversal time of PR electrolysis is 1
The time is from a fraction of a second to a few seconds. For example, in Tohoku University Senken Kenkyuho, Vol. 25, No. 2, page 155, an example in which the time is 4 seconds is shown.

However, if PR electrolysis is performed indiscriminately, the appearance quality of electrolytic copper tends to deteriorate as compared with the case of direct current electrolysis, and PR energizing conditions for preventing this have been proposed in recent years. For example, JP-A-10-88381 discloses that
The current is reversed once per minute to one hour, and the current density in the reverse direction (reverse current density) is higher than the current density in the positive direction (positive current density) (preferable range: 450 to 500 A /
m ² ) A copper electrolytic purification method characterized by maintaining and providing a constant energization stop time (preferable range: 30 seconds or more and less than 100 seconds) during switching from the reverse direction to the forward direction has been proposed. An embodiment with an increase to 360 A / m ² is disclosed.

[0004]

However, according to the method disclosed in JP-A-10-88381, the positive current density is increased to 360 A /
If it is higher than m ² , it becomes impossible to suppress the occurrence of wrinkles and bumps on the surface of the electrolytic copper. In addition, in this method, it is necessary to provide a long power outage period at the time of return to the positive electrode, so that the operation rate decreases. Further, it is necessary to make the reversal current density that promotes elution from the cathode periodically higher than the positive current density, which is disadvantageous in terms of effective use of current and equipment costs.

In view of these problems, the present invention does not generate wrinkles or bumps in electrolytic copper even when the positive current density of PR electrolysis exceeds 360 A / m ² , and eliminates the need for providing a power outage period when returning to the positive electrode. It is another object of the present invention to provide a method for electrolytically refining copper which can be operated with a reversal current density equal to or lower than a positive current density to improve productivity.

[0006]

SUMMARY OF THE INVENTION In the present invention, when copper is electrolytically refined with a periodic reversal current, the reversal current is passed for more than 60 seconds / time and the positive current is supplied for 1200 to 3000 seconds / time.
The method is a method for electrolytically refining copper. In the present invention, it is preferable that the current is supplied at a reversal current density of 0.5 to 1.0 times the positive current density.

In the present invention, a current applied by applying a positive voltage to the anode and a negative voltage to the cathode is referred to as a positive current, and the reverse current is referred to as an inverted current.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, in the PR electrolysis of copper, the energizing time of the reversing current is regulated to 60 seconds or more and the energizing time of the positive current is regulated to 1200 to 3000 seconds / times. Although the generation of wrinkles and bumps is not sufficiently suppressed even if the reversal current is supplied for a time of less than 60 seconds per time, the generation of wrinkles and bumps and the generation of grains at the edges are significantly suppressed when the current is supplied for 60 seconds or more. Moreover, there is no need to provide a power outage time when switching the polarity. For this reason, the time for applying the reversal current is limited to 60 seconds or more / time.

The reason why the surface property of electrolytic copper is improved by setting the conduction time of the reversal current to 60 seconds or more is that the electrolyte concentration gradient of the electrolyte formed unevenly near the electrode surface when a positive current is supplied. It is considered that (excessive Cu ions in the vicinity of the anode and Cu ion deficiency in the vicinity of the cathode) are canceled out by continuing the reversal current for 60 seconds or more, and the electrolyte concentration becomes uniform. Also, this time of more than 60 seconds,
Observation of the natural convection (downflow on the anode side, upward flow on the cathode side) of the electrolytic solution between the anode and the cathode in the electrolytic cell corresponds to the time when the natural convection almost stops. Therefore, when the operating conditions of the electrolysis are changed, the time for applying the reverse current may be determined in view of the situation of the natural convection.

Further, in the present invention, since the time for conducting the reversal current per operation is long, the copper is preferentially eluted from the projections such as wrinkles and bumps on the cathode surface, thereby returning to the original flat surface shape. It is considered that the formation of wrinkles and bumps on the surface of the electrolytic copper is suppressed. Nevertheless, the inversion time of the reversal current is 120
It is preferable to set the time to less than about seconds / time.

On the other hand, the reason for restricting the positive current conduction time as described above is that if the time is less than 1200 seconds per time, the amount of electrodeposition on the cathode is insufficient and the productivity is reduced, while the time exceeds 3000 seconds. In addition, the tendency of electrodeposition non-uniformity on the cathode increases and it is difficult to return to the original flat surface state even by the application of reversal current, making it difficult to eliminate wrinkles and bumps, especially with many grains at the edges This is because the shape of electrolytic copper deteriorates.

It is sufficient that the reversal current density is not more than 1.0 times the positive current density. Even if it exceeds 1.0 times, the effect of suppressing the generation of wrinkles and bumps is saturated, and only power is wasted. However, in the range where the reversal current density is less than 0.5 times the positive current density, the above-described effect gradually weakens as the reversal current density decreases. Therefore, in the present invention, the reversal current density is preferably 0.5 to 1.0 times the positive current density.

[0013]

[Example] 47 electrolytically cast anodes and 46 copper cathodes were placed in an electrolytic cell, and the PR energizing conditions were variously changed, and a total of 210 hours of PR electrolytic refining were performed for each energizing condition. About the obtained electrolytic copper, the area ratio of the smooth part where no wrinkles and nodules were generated and the state of grain generation at the edges (three-level evaluation of heavy, medium and light) were examined by visual observation.

Table 1 shows the size of the electrode and the electrolytic cell, and the electrolysis conditions common to each PR energizing condition. As shown in the table, in this PR electrolytic refining, a high current density operation with a positive current density (DK ₊ ) of 450 A / m ² was performed. In addition, the positive current conduction time (T ₊ ),
The combination of the reversal current conduction time (T ₋ ) and the reversal current density (DK ₋ ) were changed for each condition as shown in Table 2. There is no power outage period.

The results are shown in Table 2. Table 2 shows the same P
It shows the lowest value among a plurality of sheets of the R condition. As shown in the Table, T ₊ and T _- and will have a smooth surface at least 88% of the total copper surface in the embodiment which is maintained in the present invention range about particle generation also were mild. On the other hand, T ₊ and T _- the comparative example in which the present invention range is the only not smooth to at most 84% of the total copper surface had about particle generation also better than moderate in.

In the comparison in the embodiments, the inversion current
Density to positive current density ratio (DK_-/ DK₊) Is greater than 0.5
Are better than those less than 0.5 and DK_-/
DK ₊Is greater than 1.0 and there is no significant difference compared to 1.0 or less
Was.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

Thus, according to the present invention, there is an excellent effect that electrolytic copper can be produced without deteriorating the appearance quality even when operated at a high current density in the electrolytic refining of copper. In addition, since the surface condition is much better than before, the amount of additives for smoothing cathode deposition can be reduced, and the voltage can be reduced, so that the power consumption can be reduced.

In addition, productivity can be improved because the current supply time of the positive current is long, the reversal current density is 0.5 to 1.0 times the positive current density, and the current stop time is unnecessary.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Tsuneo Maruyama 6-1-1 Hibi, Tamano-shi, Okayama F-term in Mitsui Kinzoku Mining Co., Ltd. Hibiki Refinery 4K058 AA04 AA11 BA21 BB03 CA23 EC04

Claims (2)

[Claims] 1. An electrolytic refining method for copper using a periodic reversal current, wherein the reversal current is supplied for at least 60 seconds / time and the positive current is supplied for 1200 to 3000 seconds / times. Electrolytic refining method. 2. The reversal current density is set to 0.5 to 1.0 of the positive current density.
2. The electrolytic refining method according to claim 1, wherein the current is supplied twice.