Preparation of shape-controlled copper oxide powders from copper-containing solution

Preparation of shape-controlled copper oxide powders from

copper-containing solution

Younghee Ko Kim*, Doh-Hyung Riu, Soo-Ryong Kim, Byung-Ik Kim

Environmental Resource Laboratory, Korea Institute of Ceramic Engineering and Technology, 233-5 Gasan-Dong, Guemcheon-Gu,

Seoul 153-801, South Korea

Received 11 May 2001; received in revised form 6 August 2001; accepted 4 September 2001

Abstract

Shape-controlled copper oxides have been recovered from copper-containing waste etchant by neutralization with alkali

hydroxide. Large amounts of copper-containing waste etchant composed of copper chloride, hydrochloric acid and water are

generated from the printed circuit board (PCB) industry. In an environmental and economic point of view, the retrieval of the

valuable natural resource from waste is important. In the recycling process of copper oxide from the waste etchant, reaction

temperature controls the shapes and sizes of the products. Copper oxide recovered below the reaction temperature of 40 jC wasof the needle shape, while copper oxide comes in a platy shape above 40 jC. As a result of the experiments, more than 99% ofthe copper in the waste etchant was recovered as copper oxide, and its by-products are only sodium chloride and water. Physical

properties of the samples have been characterized using scanning electron microscopy (SEM), X-ray powder diffraction (XRD),

thermal gravimetric analysis (TGA) and atomic absorption spectroscopy. The particle size scatters in the range of 0.510 Am.Shape-controlled copper oxides are expected to be promising precursors for synthesizing copper powder by reduction. D 2002

Elsevier Science B.V. All rights reserved.

Keywords: Copper oxide; Copper-containing waste etchant; PCB industry; Sodium hydroxide; Neutralization

1. Introduction

Printed circuit boards (PCB) are widely used in

many electronic computer devices [1]. A chemical

milling process is commonly utilized in manufactur-

ing printed circuit boards. In a typical chemical

milling process, an etchant solution etches the cop-

per-plated printed circuit board. One of the most

common etchants in the electronic and computer

industries is the acidic etchant which consists of

hydrochloric acid (HCl) and copper chloride (CuCl2).

The disposal of the etchant without proper treatment

has posed an environmental problem because the

acidic etchant contains a significant amount of cop-

per (1015 wt.%). In addition, the disposal of the

acidic etchant without treatment results in a great

economic loss. Recently, in an attempt to solve this

problem, there have been several approaches to re-

cover copper from the etchant [24]. For example,

the copper oxychloride being used as an agricultural

ingredient is recovered by mixing the acidic etchant

with the alkali etchant that is also a waste from the

PCB industry.

0167-577X/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved.

PII: S0167 -577X(01 )00568 -7

* Corresponding author. Tel.: +82-2-3282-2472; fax: +82-2-

3282-2430.

E-mail address: [email protected] (Y.K. Kim).

www.elsevier.com/locate/matlet

May 2002

Materials Letters 54 (2002) 229237

We attempted to develop a new process of recy-

cling copper from an acidic etching solution such as

copper oxide. Copper oxide powder has been widely

utilized in many different fields such as a sintering

aid for ferrite compounds in the electronic industry,

an active constituent of fungicidal composition, a

catalyst and a pigment, etc. [5]. Various methods

are reported for the preparation of copper oxide [5].

Generally, copper oxide is produced by following

two processes. First, in pyrometallurgical process,

elemental copper is oxidized to copper oxide at 800

jC under oxygen atmosphere or air. Another com-mon process for synthesizing copper oxide is the

neutralization process. Soluble salt of copper like

copper chloride, nitrate and carbonate is neutralized

with alkali hydroxide to produce copper oxide. The

waste etchant from the PCB industry contains quite a

large amount of copper chloride and is a good source

of soluble copper salt.

In this study, we report the preparation of highly

pure copper oxide from the acidic waste of the PCB

industry by neutralization with alkali hydroxide. This

process is a very environmentally benign process

where it generates only sodium chloride and water

as by-products. The recycled copper oxide has been

characterized using SEM, XRD, TGA and atomic

absorption spectroscopy.

2. Experiments

When the PCB is fabricated, waste etchant con-

taining a large quantity of copper is produced during

the chemical milling process. The waste etchant can

be classified into two types: acidic waste etchant

(copper chloride waste etchant) and basic waste

etchant (alpine copper waste etchant). The physical

properties of the etching solution from the PCB

industry are given in Table 1. As shown in Table

1, the copper-containing etching solution that was

discharged in the PCB industry contains copper of

about 1015 wt.% concentration.

For this study, the commercial etching solution,

waste etchant provided from the PCB factory, has

been used as a starting material for synthesizing

copper oxide. The process of copper oxide prepara-

tion from the acidic etching solution is available in

Fig. 1 as a block diagram. Sodium hydroxide sol-

ution of 3350 wt.% is slowly added to the acidic

etching solution by maintaining the reaction tempera-

ture between 30 and 60 jC and then heated at 5080jC for aging. After several hours, the slurry is fil-tered and washed with water several times and sin-

tered at 100400 jC for 13 h.It is recommended that 8201100 g of 33 wt.%

sodium hydroxide solution is added to 1 l of the

acidic ething solution. If the sodium hydroxide added

is less than 820 g, the reaction is not complete, so its

product contains an excess of chlorine impurity.

Meanwhile, if the sodium hydroxide added is more

than 1100 g, an excess of sodium hydroxide is

unnecessarily consumed.

Table 1

Physical properties of acidic and alkali etching solution from the

PCB industry

Components Acidic etching

solution

Alkali etching

solution

Chemical CuCl2+HCl+

H2O

Cu(NH3)4Cl2+

NH4OH

Specific gravity

(25 jC)1.211.22 1.211.23

Cu content

(wt.%)

1015 1015

Color Green Blue

pH 14

Fig. 1. Block diagram of copper oxide synthesis.

Y.K. Kim et al. / Materials Letters 54 (2002) 229237230

The dried copper oxide is calcined at the prefer-

able temperature of 100400 jC. If the temperatureis lower than 100 jC, the calcination is not complete-ly achieved. The dried copper oxide may be calcined

at a temperature of more than 400 jC, however, forthe sake of economical energy consumption, the

temperature of 400 jC at the maximum is mostdesirable.

A Rigaku D/max-RINT 2500 diffractometer with

Cu Ka radiation was used for the XRD analysis of thesamples. Chemical analyses were performed by a

Jarrell-Ash Poliscan 61E inductively coupled plasma

(ICP) spectrometer and by a Perkin-Elmer 5000 atomic

absorption spectrophotometer. HITACHI S-4100 scan-

ning electron microscope was used for the morphology

observation of the copper oxide precipitation. Particle

size distribution was measured using a particle size

analyzer (Beckman Coulter, Model LS 230). Thermo-

gravimetric analyses were done using a Cahn TG

system 121 thermogravimetric analyzer. All samples

were heated to 700 jC at a rate of 10 jC/min undernitrogen atmosphere.

3. Results and discussion

3.1. Neutralization of the acidic etchant with alkali

hydroxide

In the neutralization process, either sodium hy-

droxide or potassium hydroxide can be used as the

alkali aqueous solution. However, considering the

easiness of obtaining a material and a unit cost of

production of the copper oxide, it is preferred to use

sodium hydroxide.

By addition of the sodium hydroxide into the

acidic etchant below 40 jC, precipitation occurs.Copper oxychloride (CuCl23Cu(OH)2) was formedin the range of pH 58, and copper hydroxide

(Cu(OH)2) above pH 9. Fig. 2 shows the neutraliza-

tion curve below 40 jC of the acidic etchant while itneutralizes the sodium hydroxide solution. However,

with the addition of the sodium hydroxide into the

acidic etching solution above 40 jC, copper oxidewas formed in all pH ranges. Fig. 3 presents the X-ray

powder diffraction (XRD) patterns of copper oxides

Fig. 2. Neutralization curve of the acidic etchant.

Y.K. Kim et al. / Materials Letters 54 (2002) 229237 231

recovered from the copper-containing waste etchant.

The sample was prepared at 30 jC to produce a cop-per hydroxide precursor and aged at 80 jC to getcopper oxide and dried at 100 jC. X-ray powder dif-fraction pattern is well matched with JCPDS No. 48-

1548 without any impurities. However, the X-ray

powder diffraction pattern is quite broad. It is as-

cribed that the sample is not fully crystallized, a sin-

tering process is required to get a highly crystallized

sample.

3.2. Effect of reaction temperature

Acidic etchants in the electronic and computer in-

dustries are composed of hydrochloric acid (HCl, 7

10%), copper chloride (CuCl2, 1925.5%) and water

(H2O, 64.574%). The addition of NaOH to the

waste etchant generates large amounts of heat by

acidbase titration since the waste etchant contains

a large amount of HCl. It leads to the instant increase

of reaction temperature of up to 80 jC. Copper oxide

Fig. 3. X-ray powder diffraction patterns of copper oxides recovered from the copper-containing waste etchant.


was formed at the beginning of the reaction. Prepared

copper oxide by this process shows a platy shape by

SEM analysis (Fig. 4a). On the other hand, the

addition of NaOH to the waste etchant while main-

taining the reaction temperature under 40 jC leads tothe copper hydroxide slurry having a bright blue

Fig. 4. Scanning electron microscopy analysis of copper oxides. (a) Reaction temperature: 60 jC. (b) Reaction temperature: 30 jC.

Fig. 5. Particle size distribution of copper oxides. (a) Aging temperature: 50 jC. (b) Aging temperature: 80 jC.


color. Aging of the copper hydroxide precursor at

5080 jC for 13 h produces to black precipitationof copper oxide. By SEM analysis, it can be seen that

the copper oxide prepared through the copper hydrox-

ide precursor has a needle shape (Fig. 4b). The

process of needle shape formation of copper oxide

during the aging period was observed by scanning

electron microscopy (SEM). The SEM analysis shows

that the copper hydroxide precursor was of the junky

shape below 40 jC of reaction temperature. However,needle-shaped copper oxides were grown from the

junky shape of the copper hydroxide 1 h after raising

the aging temperature to 80 jC, and for 3 h more, thesample was completely turned into the needle-shaped

copper oxide. It is believed that copper oxide of the

needle shape was formed during the dehydration

stage of copper hydroxide. The high purity of fine

powder and the controllability of particle shape and

size are of importance for its practical use. It is

noted that the synthesis process plays an important

role in determining the shape and size of the

particles.

3.3. Effect of aging temperature

Aging of copper hydroxide precursor was per-

formed at 5080 jC for 13 h to increase the cry-stallinity of the final product of copper oxide. Particle

Fig. 6. Scanning electron microscopy analysis of copper oxides calcined at different temperatures (a) 100 jC, (b) 300 jC, (c) 400 jC and (d)500 jC. The samples were prepared at 30 jC and aged at 80 jC.


size distribution at different aging temperatures was

measured using the particle size analyzer. The average

particle size of copper oxides aged at 50 and 80 jC for

2 h was about 10 Am (Fig. 5). The aging temperaturesdo not significantly affect the average particle size of

the copper oxide.

Fig. 7. Thermal gravimetric analysis data of copper oxides.

Fig. 8. X-ray powder diffraction patterns of copper oxides prepared at different conditions.


Table 2

Chemical analysis data of the recovered copper oxides

Sample Reaction Aging Calcination Chemical analysis data

number temperature

(jC)temperature

(jC)temperature

(jC)Cu2+

(wt.%)

Cu+

(wt.%)

Cl

(wt.%)

Na

(ppm)

Zn

(ppm)

Pb

(ppm)

Cd

(ppm)

Fe

(ppm)

Purity

as CuO

M 22 30 80 300 78.3 2.28 Tr Tr 98.0

400 78.6 2.3 Tr Tr 98.4

500 78.1 2.16 Tr Tr 28.24 40.94

3.4. Effect of calcination temperature

SEM analyses of calcinated copper oxide at differ-

ent temperatures show different morphologies with

different calcination temperatures (Fig. 6). Sample

dried at 100 jC appears to have a long needle shapehaving inhomogeneous particle size distribution.

However, the samples calcined at 400 or 500 jChave spherical shapes and homogeneous size distri-

butions. It is ascribed that recrystallization occurs at

the surface of the sample during the calcination

process.

3.5. Effect of reaction pH

The pH value (10.512) was controlled by the

amount of NaOH added while maintaining the reac-

tion temperature under 30 jC. Each sample dried at100 jC was analyzed using thermal gravimetricanalysis (TGA) (Fig. 7). Sample prepared at pH

10.5 shows weight loss at 300 jC. This weight losscan be explained by the sublimation of chloride

impurity in the sample. However, the sample prepared

at pH 12 does not show significant weight loss at the

same temperature. TGA data confirm that the entire

chloride ions of the starting material are replaced by

hydroxyl ions only above pH 12. The above results

were also confirmed by X-ray powder diffraction

data. X-ray powder diffraction data of the sample

prepared at pH 12 show only copper oxide peaks.

However, X-ray powder diffraction data of the sample

prepared at pH 10.5 show copper oxychloride peaks

accounted for an impurity besides copper oxide peaks

(Fig. 8).

3.6. Chemical analysis and yield

The chemical analysis data of copper oxide pre-

pared from waste etchant are shown in Table 2. The

purity and yield of copper oxide prepared from waste

etchant of the PCB industry are higher than 99%. It

contains impurities of Zn, Pb and Fe in ppm level.

Yield of recovered copper oxide was calculated

based on the copper concentration of the starting

material which is the commercial acidic etching

solution.

4. Conclusion

Highly pure copper oxides have been recovered

from copper-containing waste etchant of the PCB

industry. In recycling copper oxide from the waste

etchant by neutralization process using alkali hydrox-

ide solution, the reaction temperature controls the

shapes and sizes of the copper oxides. The results

are summarized in Table 3. The copper oxide recov-

ered below the reaction temperature of 40 jC was ofthe needle shape, while copper oxide comes in a platy

shape above 40 jC. As a result of the study, more than99% of the copper in the waste etchant was recovered

as copper oxide and its by-products are only sodium

chloride and water. Shape-controlled copper oxides

are expected to be promising precursors for synthesiz-

ing copper powder by reduction [6,7].

References

[1] G.R. Allardyce, A.J. Davies, D.J. Wayness, A. Singh, US Patent

5,106,454 (1992).

[2] M.A. Rabah, Hydrometallurgy 56 (2000) 75.

[3] B. Greenberg, US Patent 5,188,703 (1993).

[4] K.S. Doh, N.Y. Kim, D.K. Kim, J. Korea Solid Wastes Eng.

Soc. 14 (7) (1997) 667.

[5] H.W. Richardson, Hand Book of Copper Compounds and Ap-

plications, Marcel Dekker, New York, USA, 1997.

[6] L. Liu, T.J. Zhang, K. Cui, Y.D. Dong, J. Mater. Res. 14 (10)

(1999) 4062.

[7] J. Durisin, M. Orolinova, K. Durisinova, V. Katana, J. Mater.

Sci. Lett. 13 (1994) 688.

Table 3

The result of shape-controlled copper oxide preparation

Sample

number

Reaction

temperature (jC)Aging

temperature

(jC)

Shape of final

products

M 22 30 80 Needle shape

M 20 40 80 Needle shape

M 23 50 80 Platy shape

M 19 60 60 Platy shape


Preparation of shape-controlled copper oxide powders from copper-containing solutionIntroductionExperimentsResults and discussionNeutralization of the acidic etchant with alkali hydroxideEffect of reaction temperatureEffect of aging temperatureEffect of calcination temperatureEffect of reaction pHChemical analysis and yield

ConclusionReferences

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Preparation of shape-controlled copper oxide powders from copper-containing solution