KR101397980B1 - Remove the copper ions and process for preparing copper powder from mixed solution containing copper ions - Google Patents

Abstract

The present invention relates to a method for removing copper ions and a method for producing copper powder, which comprises adjusting a mixed solution containing copper ions to pH 0.5 to 3.5 and selectively reducing copper ions using hydrogen gas. The copper powder produced according to the present invention has a purity of 99.9% or more.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for preparing a copper powder which removes copper ions from a mixed solution containing copper ions to form a powder,

The present invention relates to a method of producing copper powder by removing copper ions from a mixed solution containing copper ions to form powders, and more particularly, to a method of producing copper powders from a mixed solution containing copper ions, nickel ions and cobalt ions To remove copper ions and to simultaneously produce a copper powder.

Copper powders are widely used in the electric and electronic industries because of their excellent conductivity and heat conductivity. Due to its excellent mechanical properties, it is used as an alloy powder by mixing with iron, tin, zinc and nickel in powder metallurgy. It is also widely used in lubricants, coatings and catalysts, and the purity of copper powder required for its use is 99.9 %.

Accordingly, there has been a demand for a technique for selectively separating copper ions from a mixed solution containing copper and reducing the copper ions to copper using a reducing agent or a technique for producing copper powders for producing copper powders.

Korean Patent Laid-Open No. 10-2005-0003164 describes a method for dissolving a copper salt such as copper sulfate or copper chloride in an aqueous solution and then adding an organic reducing agent such as hydrazine to reduce the copper ion Korean Patent Laid-Open No. 10-2010-0091532 entitled " Process for producing copper powder " describes a process for preparing a copper hydroxide precipitate by adding sodium hydroxide to an aqueous solution of copper sulfate and then producing copper powder using aliphatic aldehyde as a reducing agent . However, there is a problem in that a reducing agent used is expensive and a manufacturing cost is high, and a technique for producing copper powder by reducing copper ions from a solution in which copper ions are dissolved is described.

Also, Korean Patent Laid-Open No. 10-2012-0055365 entitled " Method for Extracting and Separating Copper, Zinc, Cadmium Nickel and Nickel by Solvent Extraction from Leachate of Secondary Metal Resources " extracts copper, zinc, cadmium and nickel from the leached solution And a method of separating copper ions, and there is a disadvantage in that the step is very complicated through a step of extracting copper ions and back-extracting them again.

Korean Patent Publication No. 10-2005-0003164 (2005. 01. 10) Korean Patent Publication No. 10-2010-0091532 (2010. 08. 19) Korean Patent Laid-Open No. 10-2012-0055365 (2012.05.31)

An object of the present invention is to provide a method for producing copper powder which selectively removes copper ions from a mixture containing copper ions to form powders.

According to an aspect of the present invention, there is provided a method for producing copper oxide, comprising: adjusting a mixed solution containing copper ions to pH 0.5 to 3.5, selectively reducing copper ions in the presence of hydrogen gas to remove copper ions to form a powder; The present invention relates to a method for producing copper powder.

Also,

a) adjusting the pH of a mixed solution containing copper ions;

b) preparing a slurry by selectively reducing copper ions by using hydrogen gas after the a) step; And

and c) separating the slurry from the solution, wherein the copper ions are removed to form a powder.

Further, the present invention relates to a method for producing copper powder by removing copper ions from a mixed solution containing copper ions, copper ions, nickel ions and cobalt ions in the step a).

Further, the present invention may further comprise: washing and drying the separated slurry after step c); And removing the copper ions to form a powder.

The present invention also relates to a method for producing copper powder by removing copper ions, which is performed at a temperature ranging from 170 ° C to 210 ° C during the reduction reaction in the step b).

Also, the present invention relates to a method for producing copper powder by removing copper ions, which is characterized in that the hydrogen partial pressure is 20 kg / cm ² to 50 kg / cm ² during the reduction reaction in the step b).

Further, the present invention relates to a method for producing copper powder by removing copper ions to form a powder, wherein a trivalent iron ion is further added during the reduction reaction in the step b).

The present invention also relates to a method for producing copper powder by removing copper ions to form a powder, wherein the concentration of the trivalent iron ion is 50 to 100 ppm.

The present invention also relates to a method for preparing a compound of formula (I) wherein, in the step b), sodium hexametaphosphate, sodium polyphosphate, sodium phosphate, sodium pyrophosphate and lignosulfonate and lignosulfonates. The present invention also relates to a method for producing copper powder by removing copper ions.

The present invention also relates to a method for producing copper powder by removing copper ions to form a powder, wherein the additive is included in an amount of 1 to 2 parts by weight based on 100 parts by weight of a mixed solution containing copper ions.

According to another aspect of the present invention, there is provided a copper powder having a purity of 99% to 99.9% of a copper powder produced by any one of the above methods.

Further, the present invention can selectively remove copper ions from a mixed solution containing copper ions, and at the same time, it is possible to produce copper powders with high purity, and the manufacturing process is simple and economical.

Hereinafter, each configuration of the present invention will be described in detail.

The present invention relates to a method of producing copper powder by controlling a mixed solution containing copper ions at a pH of 0.5 to 3.5 and selectively reducing copper ions in the presence of hydrogen gas to remove copper ions to form powders, The

a) adjusting the pH of a mixed solution containing copper ions;

b) preparing a slurry by selectively reducing copper ions by using hydrogen gas after the a) step; And

c) separating the slurry from the solution; .

In the step a), the pH of the mixed solution containing copper ions is controlled. The mixed solution containing the copper ions may be a mixture of copper ions, nickel ions and cobalt ions. However, the present invention is not limited thereto, and a mixed solution containing copper ions can be used.

In the present invention, the pH of the mixed solution containing copper ions is preferably in the range of 0.5 to 3.5, preferably in the range capable of selectively reducing copper ions. When the pH range is less than 0.5 or more than 3.5, copper hydrate Or the reduction rate of the copper ion is remarkably lowered. When adjusting the pH of the mixed solution, it is preferable to use an acid or an alkali solution, preferably sulfuric acid or an aqueous solution of sodium hydroxide. However, it is not limited thereto.

In the step b), a mixed solution containing copper ions is adjusted to pH 0.5 to 3.5, and then copper ions are selectively reduced using hydrogen gas to produce a slurry containing copper metal. The hydrogen gas partial pressure is 20 kg / cm < ² > to 50 kg / cm < ² >.

In general, the reduction of metal ions by hydrogen gas is greatly influenced by the partial pressure of hydrogen gas and the pH of the solution. In the case of copper ions, it can be reduced to copper metal at all pH ranges when the hydrogen partial pressure is thermodynamically 1 atm (See FIG. 2). However, in order to reduce the copper ion to a high selective purity and a high reduction ratio, the hydrogen gas partial pressure is preferably 20 kg / cm ² to 50 kg / cm ² , .

Therefore, the reduction rate of copper ion may be 100% at the hydrogen gas partial pressure range and pH range during the reduction reaction of copper ion, and since the purity of the copper powder to be produced may be 99.9% or more, It is preferable to satisfy it.

In addition, when the copper ion is reduced to copper metal, the reaction is preferably performed at a temperature in the range of 170 ° C to 210 ° C. When the temperature is lower than 170 ° C, the reduction rate of copper ion is lowered. . Accordingly, performing the reduction reaction of copper ions within the above range can increase the reduction rate of copper ions including copper and the purity of the copper powder.

Further, in the present invention, trivalent iron ions or additives may be further added during the reduction reaction, and further adding the trivalent iron ions at a concentration of 50 ppm to 100 ppm is preferable for shortening the reduction reaction time, It becomes a factor.

The additive may be one or two selected from sodium hexametaphosphate, sodium polyphosphate, sodium phosphate, sodium pyrophosphate and lignosulfonates, and the like. But is not limited thereto. It is preferable to use sodium hexametaphosphate. When the additive is further added to perform the reduction reaction, it is possible to make the particle size of the produced copper powder more homogeneous and to prevent the phenomenon of aggregation between the particles.

It is preferable that the additive is added in an amount of 1 to 2 parts by weight based on 100 parts by weight of the mixed solution containing copper ions. In the case where the additive is included in the range, copper powder is prevented from being coated inside the reactor And the bundle phenomenon between the particles of the copper powder can be prevented.

Further, the present invention may further comprise: washing and drying the separated slurry after step c); The separation may be performed by using a filter net or by any one of centrifugal separation, grinding, screw press, filter press, belt press, etc. However, if the liquid and slurry can be separated from each other, Can be used without being.

When washing the separated slurry, a counter current or an ultrasonic washing machine may be used, and it is necessary to sufficiently clean the surface of the copper powder so as not to adsorb nickel or cobalt ions. However, it is not limited thereto.

In addition, the drying is for completely removing moisture on the surface of the separated copper powder, and in order to prevent surface oxidation of the copper powder which may occur during drying, it is preferable to perform the drying at a temperature of 30 to 90 ° C in a vacuum drier (vacuum degree: 10 torr.) Do. However, any drying method capable of removing moisture while preventing surface oxidation of the copper powder can be used without limitation.

According to still another aspect of the present invention, there is provided a copper powder produced by a method for producing a copper powder by removing the copper ion to form a powder, wherein the copper powder has a purity of 99.9% or more.

According to the present invention, copper ions can be selectively removed from a mixed solution in which copper ions, nickel ions and cobalt ions are mixed, and simultaneously copper powders can be produced by a method for producing copper powders by removing copper ions to form powders , The process is simple and the manufacturing cost can be lowered compared with the conventional method. In addition, it is possible to reduce the copper ion by hydrogen gas to increase the reduction ratio to 100%, thereby increasing the yield of the copper powder. Also, copper powder having a purity of 99.9% or more and excellent in purity can be produced.

FIG. 1 is a manufacturing process diagram of a copper powder manufacturing method for forming a powder by removing copper ions from a nickel, cobalt, and copper mixed solution used in the present invention.
2 is an Eh-pH graph (concentration: 1M, temperature: 25 ° C) of copper and nickel.
3 is an XRD pattern of a copper powder produced according to Example 5 of the present invention.
Fig. 4 (a) is an SEM image of the copper powder produced according to the fourth embodiment of the present invention, and Fig. 4 (b) is an SEM image of the copper powder prepared according to the comparative example 14 of the present invention. (C) is an SEM image of copper powder produced according to Example 10 of the present invention, and (d) is an SEM image of copper powder produced according to Example 11 of the present invention.

Hereinafter, the present invention will be described in more detail with reference to examples. The following examples are only illustrative of the present invention in detail, but the present invention is not limited thereto.

The following physical properties were measured by the following methods.

1. Atomic absorption analyzer measurement

The atomic absorption spectrometer was measured using Atomic Absorption Spectrometer, model Perkin Elmer, model AA-400. A sample to be measured was diluted with 10% hydrochloric acid to prepare a sample. At this time, the wavelength was analyzed at 324.8 nm of copper, 248.3 nm of iron, 240.7 nm of cobalt and 232.0 nm of nickel.

2. XRD measurement of copper powder

RIGAKU's R4-200 model was used. About 0.4 g of a powder sample was prepared and measured at a scanning angle of 10 to 80 ^° C. Matching XRD peaks were confirmed using SRD Data process software.

3. SEM measurement of copper powder

The particle size and shape of the copper powder were measured using an SEM (Japan, JEAL Co., model name: JEL6380LA).

[Preparation Example] Preparation of a mixed solution of copper ion, nickel ion and cobalt ion

(NiSO ₄ 6H ₂ O) 134.36 g Cobalt sulfate (CoSO ₄ 7H ₂ O) 14.31 g ₃ ) and 98.20 g of copper sulfate (CuSO ₄ 5H ₂ O) were dissolved in 500 ml of distilled water, and the total volume of distilled water was adjusted to 1 L And distilled water was added thereto. The concentrations of the metal ions in the mixed solution are shown in Table 1, which is similar to the composition of the mat-phase leach solution obtained in the deep-sea manganese nodule smelting.

(Table 1)

[ Example  One]

1 L of the mixed solution prepared in the above Preparation Example was added to a 2 L reaction vessel (manufactured by PARR, model 4843, USA), and the pH of the mixed solution was adjusted to 1.0 using sulfuric acid. Then, the temperature of the reactor was adjusted to 180 ° C., the mixture was stirred at 300 rpm, hydrogen gas was supplied at 25 Kg / cm ^2, and a reduction reaction was carried out for 120 minutes to produce a sludge containing copper metal.

After completion of the reduction reaction, the temperature of the reactor was cooled to 30 ° C, and the reaction filtrate and the resulting sludge were subjected to solid-liquid separation using a filter paper (product of Toyo Roshi Kai Noom, 5C type, diameter 110 mm). The obtained sludge was washed with distilled water in an ultrasonic washing machine and sufficiently washed until no nickel ion or cobalt ion was detected in the washing liquid (1L × 3 times). Since the obtained sludge contained moisture, The copper powder was dried in a vacuum dryer (vacuum degree: 10 torr) at a temperature of 90 ° C for 6 hours to prepare a copper powder whose moisture was completely removed.

The reduction rate of the copper ion and the purity of the copper powder produced during the reduction reaction were measured and are shown in Table 6 below.

[Examples 2 to 7]

The reduction reaction was carried out in the same manner as in Example 1 to prepare a copper powder. The experimental conditions are shown in Table 2 below. The reduction rate of the copper ion and the purity of the copper powder produced during the reduction reaction were measured and are shown in Table 6 below.

(Table 2)

[Example 8]

Ferric sulfate (Fe ₂ (SO ₄ ) ₃ ) was added to 1 L of the mixed solution prepared in the above Preparation Example so that the concentration of ferric ion was 50 ppm. Was added to a 2 L reaction vessel (manufacturer PARR, model 4843) and the mixed solution was made to pH 3.0 using sulfuric acid. Then, the temperature of the reactor was adjusted to 180 ° C, the mixture was stirred at 300 rpm, hydrogen gas was supplied at 30 Kg / cm ^2, and a reduction reaction was performed for 120 minutes to prepare a sludge containing copper metal.

After completion of the reduction reaction, the temperature of the reactor was cooled to 30 ° C, and the reaction filtrate and the resulting sludge were subjected to solid-liquid separation using a filter paper (product of Toyo Roshi Kai Noom, 5C type, diameter 110 mm). The obtained sludge was washed with distilled water in an ultrasonic washing machine and sufficiently washed until no nickel ion or cobalt ion was detected in the washing liquid. (1 L x 3) Since the obtained sludge contained moisture, The copper powder was dried in a dryer (vacuum degree: 10 torr) at a temperature of 90 ° C for 6 hours to prepare a copper powder whose moisture was completely removed.

The reduction rate of the copper ion and the purity of the copper powder produced during the reduction reaction were measured and are shown in Table 6 below.

[Examples 9 to 11]

Copper powder was prepared under the same experimental conditions as in Example 8 except that the concentration of trivalent iron or sodium hexametaphosphate was controlled in the mixed solution. The concentration of trivalent iron ion or the amount of sodium hexametaphosphate is shown in Table 3 below, and the reduction rate of copper ion and the purity of the copper powder produced during the reduction reaction were measured and shown in Table 6 below.

(Table 3)

[Comparative Example 1]

1 L of the mixed solution prepared in the above Preparation Example was added to a 2 L reaction vessel (manufactured by PARR, Model 4843, USA), and the pH of the mixed solution was adjusted to 5.0 using sulfuric acid. Then, the temperature of the reactor was adjusted to 180 ° C., the mixture was stirred at 300 rpm, hydrogen gas was supplied at 25 Kg / cm ^2, and a reduction reaction was carried out for 120 minutes to produce a sludge containing copper metal.

After completion of the reduction reaction, the temperature of the reactor was cooled to 30 ° C, and the reaction filtrate and the resulting sludge were subjected to solid-liquid separation using a filter paper (product of Toyo Roshi Kai Noom, 5C type, diameter 110 mm). The obtained sludge was washed with distilled water in an ultrasonic washing machine and sufficiently washed until no nickel ion or cobalt ion was detected in the washing liquid. (1 L x 3) Since the obtained sludge contained moisture, The copper powder was dried in a dryer (vacuum degree: 10 torr) at a temperature of 90 ° C for 6 hours to prepare a copper powder whose moisture was completely removed.

The reduction rate of the copper ion and the purity of the copper powder were measured during the reduction reaction and are shown in Table 7 below.

[Comparative Examples 2 to 9]

The copper powder was prepared in the same manner as in Comparative Example 1, and the conditions of the experiment are shown in Table 4 below. The reduction rate of the copper ion and the purity of the copper powder were measured during the reduction reaction and are shown in Table 7 below.

(Table 4)

[Comparative Example 10]

Ferric sulfate (Fe ₂ (SO ₄ ) ₃ ) was added as an additive to 1 L of the mixed solution prepared in the above Production Example, so that the concentration of ferric ion was 10 ppm. Was added to a 2L reaction vessel (manufacturer PARR, model 4843) and the pH of the mixed solution was adjusted to 3.0 using sulfuric acid. Then, the temperature of the reactor was adjusted to 180 ° C., and the reaction was continued for 120 minutes while maintaining the hydrogen gas at 30 Kg / cm ² while stirring at 300 rpm to produce a sludge containing copper metal.

After completion of the reduction reaction, the temperature of the reactor was cooled to 30 ° C, and the reaction filtrate and the resulting sludge were subjected to solid-liquid separation using a filter paper (product of Toyo Roshi Kai Noom, 5C type, diameter 110 mm). The obtained sludge was washed with distilled water in an ultrasonic washing machine and sufficiently washed until no nickel ion or cobalt ion was detected in the washing liquid. (1 L x 3) Since the obtained sludge contained moisture, The copper powder was dried in a dryer (vacuum degree: 10 torr) at a temperature of 90 ° C for 6 hours to prepare a copper powder whose moisture was completely removed.

The reduction rate of the copper ion and the purity of the copper powder were measured during the reduction reaction and are shown in Table 7 below.

[Comparative Examples 11 to 15]

Copper powder was prepared under the same conditions as in Comparative Example 5 except that the concentration of trivalent iron or sodium hexametaphosphate was controlled in the mixed solution. The concentration of trivalent iron ion or the amount of sodium hexametaphosphate is shown in the following Table 5, and the reduction rate of copper ion and the purity of the copper powder produced during the reduction reaction were measured and shown in Table 7 below.

(Table 5)

(Table 6)

(Table 7)

In Example 1 and Comparative Example 2, the reduction ratio of copper ions according to the pH range of the mixed solution was examined. In Example 1 with a pH of 1.0 and Example 2 with a pH of 3.0, It can be seen that the copper ions in the mixed solution are all reduced at the time of elution, and that the purity of the reduced copper powder is 99.9% or more, so that a copper powder with a very high purity can be obtained. However, in Comparative Example 1 in which the pH of Table 7 is 5.0, it can be seen that a part of copper ions precipitates as copper hydrate before the reduction reaction of copper ions, so that the reduction reaction of copper ions does not occur properly. In Comparative Example 3, it was also found that a part of copper ions precipitated as copper hydrate. Also, in Comparative Example 2 in which the pH was 0.3, it was confirmed that the reduction rate of copper remarkably decreased.

In Examples 2 to 3, the copper ions were reduced at 180 ° C and 200 ° C during the reduction reaction, respectively. After 90 minutes, the copper ions were all reduced. The purity of the copper powder produced was 99.9% As shown in Fig. However, in Comparative Example 4 having a temperature of 165 ° C in the reduction reaction and Comparative Example 5 having a temperature of 150 ° C in Table 7, although the reaction time was 120 minutes, a part of the copper ion was not reduced and the reduction ratio was less than 90% , And the purity of the reduced copper powder is also 90% or less. On the other hand, in Comparative Example 6 in which the reaction temperature was 220 ° C, there was no significant change in the copper reduction rate according to the change of time as compared with the case of 200 ° C, but the purity of the copper powder was lowered due to reduction precipitation of nickel and cobalt. In Example 2 and Examples 4 to 7, the partial pressure of hydrogen gas was reduced from 20 kg / cm ² to 50 kg / cm ² The reduction rate of copper with time increases slightly as the partial pressure of hydrogen gas increases. However, in all cases, the reduction rate reaches 100% after 90 minutes of reduction reaction. In this case, The purity was also over 99.9%. On the other hand, when the partial pressure of the hydrogen gas is 10 Kg / cm ² Comparative Example 7, in which the partial pressure of hydrogen gas was 15 Kg / cm ² , showed a reduction ratio of less than 90% despite the reduction reaction time of 120 minutes. In Comparative Example 9 in which the partial pressure of hydrogen gas was 60 Kg / cm ² , the reduction rate of copper with time varied from 50 kg / cm ² The nickel and cobalt were partially reduced as in Comparative Example 6, and the purity of the copper powder was lowered.

Therefore, when the copper ions are selectively removed from the mixed solution containing copper and the copper powder is produced, the pH of the solution, the partial pressure of the hydrogen gas as the reducing agent selectively remove the copper ions, It can be seen that this is an important reaction condition that can be produced.

In Table 6, Examples 8 to 9 illustrate the effect of trivalent iron ions on the reduction reaction. To add trivalent iron ions to the mixed solution, ferric sulfate (Fe ₂ (SO ₄ ) ₃ ) The effect of trivalent iron ions was investigated. Example 8 in which 50 ppm of trivalent iron was added and Example 9 in which 100 ppm was further added showed that copper ions were reduced to 100% after 60 minutes of the reduction reaction and the reduction reaction was terminated, The reduction reaction rate of copper is higher than that of copper reduction reaction. Also, the purity of the copper powder produced at this time is also 99.9% or more, indicating a very high purity. However, in Comparative Examples 10 to 12 in which trivalent iron ions were added at 10 ppm, 30 ppm, or 40 ppm, copper was reduced to 100% within 90 minutes, and the reduction rate of copper was lower than that in the case where trivalent iron ions were not added It can be seen that it has not improved much. On the other hand, when 120 ppm of trivalent iron ion was added, as shown in Comparative Example 13, the reduction rate of copper was similar to that of 100 ppm of trivalent iron, but the purity of copper was somewhat lowered to 99.90%.

Therefore, the addition of trivalent iron ions is also important, but the addition of trivalent iron ions also plays an important role in the reduction reaction rate and copper purity.

In order to prevent the homogeneity of the copper powder produced in the last step and to prevent the copper powder from being coated on the surface of the high-temperature high-pressure reactor, Sodium Hexa-Meta Phosphate [(Na ₂ PO ₃ ) ₆ ] And the effect was examined. Examples 10 to 11 in which 1.0 part by weight or 2.0 parts by weight of sodium hexametaphosphate was added to reduce the purity of the copper powder were shown in Table 10, There was no significant difference. However, as shown in the SEM image photographs of FIGS. 4 (c) and 4 (d), it can be seen that there is no aggregation between the particles. In this case also, the copper coating phenomenon did not occur on the surface of the reaction vessel. On the other hand, FIGS. 4 (a) and 4 (b) show that the aggregation phenomenon between particles can be visually confirmed by adding sodium hexametaphosphate and 0.5 part by weight of sodium hexametaphosphate (Comparative Example 14) Coating phenomenon also occurred.

Copper powders prepared with 3.5 parts by weight of sodium hexametaphosphate were also similar in appearance to SEM images (FIG. 4 (a)) similar to Example 1 in which no sodium hexametaphosphate was added Could know.

Also, when 3.0 parts by weight of sodium hexametaphosphate was added (Comparative Example 15), the reduction rate of copper was slow.

Claims (11)

A method for producing copper powder, which comprises adjusting a mixed solution containing copper ions to pH 0.5 to 3.5 and selectively reducing copper ions in the presence of hydrogen gas to remove copper ions to form powders. The method according to claim 1,
a) adjusting the pH of a mixed solution containing copper ions;
b) preparing a slurry by selectively reducing copper ions by using hydrogen gas after the a) step; And
c) separating the slurry from the solution; ≪ / RTI > to form a powder. 3. The method of claim 2,
Wherein the mixed solution containing copper ions in step a) is a mixture of copper ions, nickel ions and cobalt ions, and removing the copper ions to form powders. 3. The method of claim 2,
Washing and drying the separated slurry after step c); c-1) washing and drying the separated slurry; And removing the copper ions to form a powder. 3. The method of claim 2,
Wherein the reducing step is carried out in a temperature range of 170 ° C to 210 ° C during the reduction reaction in the step b). 3. The method of claim 2,
Wherein the hydrogen gas partial pressure is 20 kg / cm ² to 50 kg / cm ² during the reduction reaction in the step b). 3. The method of claim 2,
Wherein the copper ions are added to form a powder by adding a trivalent iron ion during the reduction reaction in the step b). 8. The method of claim 7,
Wherein the concentration of the trivalent iron ion is 50 to 100 ppm. 3. The method of claim 2,
Wherein one or more additives selected from sodium hexametaphosphate, sodium polyphosphate, sodium phosphate, sodium pyrophosphate and lignosulfonate are further added during the reduction reaction in the step b) Of copper powder. 10. The method of claim 9,
Wherein the additive is added in an amount of 1 to 2 parts by weight based on 100 parts by weight of the mixed solution containing copper ions. delete

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