Indian Journal of Chemical Technology

Vol. 18, January 2011, pp. 37-44

Electrowinning of copper powder from copper sulphate solution in presence

of glycerol and sulphuric acid

S G Viswanatha*

& Sajimol George

b

aDepartment of Chemistry, Laxminarayan Institute of Technology, R T M Nagpur University, Nagpur 440 033, India

Received 31 March 2010; accepted 11 October 2010

Copper powder was obtained by electrowinning copper from glycerol and sulphric acid medium. The morphology and

particle size of these powders were studied. Dendrites were observed in the powder obtained from solutions containing only

glycerol. Powder obtained from the sulphuric acid glycerol medium the particles were spherical or round in shape and more

than 90% of particles were below 100 µm. The nano-particles were also observed that were in the range of 200-700 nm. The

apparent density of copper powder decreased with increasing concentration of sulphuric acid and glycerol that might be

helpful in assessing the nature and particle size. The stability of the powder and current efficiency were also studied.

Keywords: Electrowinning, Cadmium, Stability, SEM, Particle size, Avrami-Erofeev kinetics

Copper powder is used for manufacturing of refractory materials, fabrication of many industrial and machine parts such as clutch phasing, brake linings etc. Zheng and Jiang

1 studied the process of

electrolytic manufacturing of copper powder by

electrolysis of copper salts using current density of 6 A/dm

2. Hou

2 studied structural and surface defects

of electrodeposited copper powder by electrowinning process. Pattabhiraman et al

3 presented briefly the

electrolytic method of copper powder deposition from copper sulphate and chloride baths. Kokila et al.

4

developed a method of electroplating by copper from solution containing copper-sulphamate and copper-EDTA complexes. Delplancke et al.

5 have studied

electrowinng process of copper at high current density. Paster and Miguel

6 studies showed that the

morphological patterns of copper powder, obtained

from moderately concentrated copper solutions, depend on current densities. Muresan et al.

7 studied

electrowinning of copper from different sulphate electrolytes. Borikar et al.

8 studied elecrowinning of

copper from sulphuric acid and acetone media. Viswanath and George

9 studied electrowinning of

cadmium from sulphuric acid and glycerol media. In the present investigation, an attempt has been

made to study the morphology and particle size of

electrowon copper powder from different percent of

glycerol and H2SO4 concentrations. A method has

been suggested for the determination of approximate

density (apparent density) of copper powder. These

densities may help to assess the nature and size of

particles of the powder. The chemical kinetics

and Avrami-Erofeyev kinetics of electro deposition

of copper powder was studied. Avrami-Erofeyev

kinetics n value can be related to the dimension of

the particle.

Experimental Procedure Instrument

The bath solution (CuSO4, H2SO4 and glycerol) was

taken in a single compartment of two-electrode cell.

The electrowinning experiments were performed

using copper plate (6 cm × 0.5 cm × 1 mm) as cathode

and gold plate ( same dimensions as copper plate) as

anode. Current was supplied by Regulated DC Power

Supplier Model L3202 (Aplab). Current and voltage

were indicated digitally by the instrument itself. All

the experiments are carried out at the room

temperature. The temperature of the bath remained

almost constant during the experiment. 0.5 amp of

current is applied to the bath. The current variation is

± 0.01 A. The particle size and morphological

analysis was performed on Fritsch particle sizer -

ANALYSETTE 22 and scanning electron microscope

(SEM) JEOL, JXA 240A operated at 15 kV

respectively at JNARDDC, Wadi, Nagpur, India. Method of estimation of copper

The glycerol is taken as volume percent and acid

concentration is taken as normality. The total volume

of the electrolytic bath solution is made up to ———————

*Corresponding author (E-mail: gortiviswanath@yahoo.com)

INDIAN J CHEM. TECHNOL, JANUARY 2011

38

200 mL. 2 mL of bath solution is taken at 10 min

intervals and analyzed for copper by titration of the

solution against 0.01N EDTA using FSB-F indicator,

and the kinetics of copper deposition was studied.

The deposition was continued for four hours to get

sufficient quantity of powder for different types of

analysis. The copper concentration initially taken is

0.2 N for all experiments. The percentage of glycerol

and sulphuric acid concentration are varied. The

deposit is removed from the cathode by simple

scratching with glass rod in the solution. The deposit

is collected by filtering the solution through filter

paper and washed thoroughly with distilled water

several times and then with acetone two or three

times to remove water from the deposit. This is

dried in a air oven at about 110°C. The powder is

removed from the filter paper and stored in air tight

glass bottle.

Standard electrode potential of copper

The emf of copper-saturated calomel cell was

measured at different concentration of sulphuric acid

and glycerol using digital potentiometer of model EQ-

DGM. ln(CCu++), where CCu++ is the concentration of

copper, is plotted against emf of the cell. The

intercept on emf-axis, when ln(CCu++) is zero, i.e.,

copper activity is one, gives emf of the cell. From emf

value standard electrode potential of copper is

determined. The standard electrode of copper is given

in Table 1.

Determination of apparent density of copper powder

An empty dry density bottle is taken and weighed

(W1). Then, it is filled with distilled water and

weighed again (W2). Volume of the density bottle is

given by (W2 – W1)/ D, where D is the density of

water at that temperature. The volume of density

bottle is V1. The same dry empty bottle is filled with

about 1 to 1.5 g of copper powder and weighed (W3.)

and then filled with water and weighed again (W4).

The mass of the water is (W4 –W3) and the volume of

water is (W4 – W3)/D. Now this volume is V2 in the

presence of copper powder. Therefore volume of the

copper powder is, (V1 –V2). Hence apparent density of

copper powder is (W3 –W1)/(V1- V2). In the Table 2

apparent density of copper powder, obtained at

different concentrations of sulpheric acid and percent

of glycerol is presented.

Cathodic current efficiency

Study of current efficiency (CE) was performed by

measuring the copper content in the bath solution. The

metallic copper actually deposited was estimated by

titrating the bath solution against standard EDTA

using FSB-F indicator. Based on the current used for

the particular period of electrolysis, the theoretical

expected weight of copper deposition was calculated

using Faraday’s Law

W = Z It … (1)

Where, W, Z, I and t are theoretically expected

weight of copper deposit, electrochemical equivalent

of copper, current in amperes and time in seconds

respectively.

The CE was calculated using the relation,

CE = (w/ W) × 100 … (2)

where, w is the weight of the copper deposited in

the actual practice. The data is presented in Table 3.

Determination of stability of copper powder

Copper powder was stored for forty-five days in an air tight sealed bottle. About one gram of copper powder, was weighted accurately, was taken in 100 mL 0.5 N H2SO4. The solution was stirred with a

magnetic stirrer for one hour. The solution was filtered and the dissolved copper in the filtrate was estimated by titrating the filtrate against standard

Table1―Standard electrode potential of copper at various

concentration of sulphuric acid and glycerol medium

H2SO4

concentration

Percent of glycerol (%) and

Standard electrode potential of copper (V)

(N) 0 5 10 15 20

0.0 0.316 0.293 0.305 0.307 0.306

0.5 0.306 0.310 0.311 0.312 0.326

1.0 0.283 0.299 0.304 0.294 0.256

1.5 0.276 0.313 0.297 0.287 0.268

2.0 0.272 0.296 0.287 0.300 0.270

Table 2―Apparent density of copper at various concentration of

sulphuric acid and glycerol medium

H2SO4

concentration

Percent of glycerol (%) and

Apparent density of copper (g/mL)

(N) 2.5 5 7.5 10 15

0.0 6.1 6.0 5.3 4.2 3.1

0.5 6.0 5.3 4.6 3.2 2.8

1.0 5.3 4.2 3.4 2.5 2.2

Table 3―Cathodic current efficiency of copper winning process

at different concentration of sulphuric acid and glycerol medium

H2SO4

concentration

Percent of glycerol (%) and

Apparent density of copper (g/mL)

(N) 2.5 5 7.5 10 15

0.0 48.5 59.1 67.5 73.9 74.5

0.5 64.7 66.5 70.2 76.0 77.7

1.0 57.0 63.4 65.4 84.2 85.0

VISWANATH & GEORGE: ELECTROWINNING OF COPPER POWDER FROM COPPER SULPHATE SOLUTION

39

EDTA (0.01N) using FSB-F indicator. Since copper powder is susceptible to oxidation and forms copper oxide (CuO). This oxide reacts with sulphuric acid and forms copper sulphate. But copper does not react with sulphric acid. The stability of copper was

estimated using the formula

Stability =

100exp

×

erimentthefortakenactuallycoppermetallicofWeight

dundissolvepowdermetallicofWeight

… (3)

The data are presented in the Table 4. Particle size analysis

The distribution of copper particle size is shown in

Fig. 1 and the data of distribution is given in Table 5.

With 15% glycerol in the bath solution, the

cumulative frequency of partial size decrease by about

5.42%. It is also observed that the concentration of

sulphuric acid in range of 0.0 to 1.0 N and glycerol in

5 to 10% range give very desirable or good particle

that show some nano character. This is evident from

the SEM studies also. Morphologic investigation

SEM micrographs of copper powder are shown in

Fig. 2. In Table 6, the relevant physical data of

respective powders are presented. These results show

that lower is the apparent density smaller is the

particle size of electrodeposited powder. Reaction mechanism of electrodepositon of copper

The important electrode reactions during the

electrowinning process are given below. Since

copper, sulphate and sulphuric acid are strong

electrolytes, so they dissociated completely. The

water molecule dissociates as:

CuSO4 = Cu 2++ SO42- … (4)

H2 SO4

= 2H+ + SO42 … (5)

4H2O � 4H+ + 4OH- … (6)

Reaction at cathode

Cu2+ + 2e = Cu … (7)

2H+ + 2e = H2 … (8)

The net cathodic reaction is

Cu2+ + 2H+ + 4e = Cu + H2 … (9) Reaction at anode

40H- = 2O + 2H2O + 4e … (10)

2O = O2 … (11)

The net cell reaction is:

Cu2++2H+ + 4HO-=Cd+H2+ O2 +2H2O … (12) Oxidation of glycerol

These reactions are discussed by Viswanath and

George9. While liberated oxygen at anode reacts with

glycerol and forms several products, the two primary

alcoholic groups in glycerol are capable of being

oxidized to aldehide and then to the carboxyl group.

CH2 OH- CHOH- CH2 OH →CHO. CHOH- CH2 OH →

(glycerol) (glyceraldehydes)

COOH. CHOH- CH2 OH →

(glyceric acid)

COOH. CHOH - COOH. → COOH. CO – COOH

(tartonic acid) (mesoxalic acid) … (13)

The secondary alcoholic group is oxidized to

carbonyl group. CH2 OH- CHOH- CH2 OH → CH2 OH- CO- CH2 OH →

(glycerol) (dihydroxy acetone)

COOH. - CO – COOH … (14) (mesoxalic acid)

Kinetics of electrodeposition of copper

These types of kinetic studies have been carried out

in the study of electrowinng of different metals, like

copper, cadmium, nickel and zinc from aqueous

acetone8,10-12

, glycerol9 and 1,4-dioxne

13 medium

containing either sulphuric acid or ammonia.

Table 4―Stability of copper powder obtained at various

concentration of sulphuric acid and glycerol medium

H2SO4

concentration

Percent of glycerol (%) and

stability of copper powder (g/mL)

(N) 2.5 5 7.5 10 15

0.0 49.2 61.9 64.4 72.1 74.0

0.5 44.1 54.3 72.1 71.1 78.0

1.0 56.8 64.4 69.5 74.6 76.7

Table 5―Particle size of Cu in different concentrations of

sulphuric acid and glycerol medium

Concentration % of particles in different range of µm

H2SO4 (N) +

glycerol (%)

1.95-

22.28

22.28-

42.33

42.33-

68.49

68.49-

94.40

94.40-

290.19

0+7.5 13.52 21.88 27.00 17.23 20.39

0+15 20.70 23.23 27.15 13.88 15.04

0.5+10 28.05 26.26 20.47 12.52 12.70

0.5+15 21.89 24.23 26.38 21.94 5.56

1.0+5 27.24 28.75 24.15 11.81 8.06

1.0+10 30.07 30.07 21.42 9.71 8.76

INDIAN J CHEM. TECHNOL, JANUARY 2011

40

Chemical kinetics

The kinetics of electrodeposition of copper in the

presence of different concentration of sulphuric acid

and glycerol was studied. α, the fraction deposited

is defined as:

α = Ct /Ci … (15)

where Ci and Ct are initial concentration and

concentration of Cu2+

at any time t, respectively. The

rate of change of concentration with respective time is

expressed as:

dα/dt = k(1- α)n … (16)

where n and k correspond to the order of reaction and

reaction rate constant respectively. (1-α) is the fraction

of copper metal deposited. For zero order reaction the

integrated form of the above equation is written as:

α = kt … (17)

Fig. 1―Distribution of particle size of cadmium powder obtained from different media (a) 7.5% glycerol, (b) 15% glycerol, (c) in 0.5 N

H2SO4 + 10% glycerol, (d) 0.5 N H2SO4 + 15% glycerol, (e) 1N H2SO4 + 5 % glycerol and (f) 1N H2SO4 + 10% glycerol

VISWANATH & GEORGE: ELECTROWINNING OF COPPER POWDER FROM COPPER SULPHATE SOLUTION

41

Fig. 2―SEM microphotographs of copper powder obtained from different media (a) 7.5% glycerol, (b) 15% glycerol, (c) in 0.5 N H2SO4

+ 10% glycerol, (d) .5 N H2SO4 + 15% glycerol, (e) N H2SO4 + 5 % glycerol and (f) 1N H2SO4 + 10% glycerol

INDIAN J CHEM. TECHNOL, JANUARY 2011

42

Plot of α verses time gives a linear plot passing

through the origin with the slope equals to k. Fig. 3(a-c)

represents the zero order plots for the

electrodeposition of copper in different concentrations

of sulphuric acid and glycerol. The reaction rate

constants (k) of the electrodeposition kinetics are

given in Table 7. First few minutes of the kinetics

does not obey the zero order. Plot of ln(1-α) against

time gives a straight line but it does not pass through

origin, i.e., zero time. Experimental α values are less

than that of computed values from the zero order

kinetic equation. This may be due to induction period

of the reaction.

Avrami-Erofeev kinetics

The chemical kinetics of electrodeposition of

copper is tried to correlate with Avrami-Erofeev

kinetics. Avrami-Erofeev kinetics gives some clue

about the morphology and size of the particle. The

equation is given as:

(1-α) =exp (-ktn) … (18)

and the logarithmic form of equation is written as:

ln{-ln(1-α)} = n ln(t) + ln(k) … (19)

where n and k are order of reaction and rate

constant of the reaction respectively. Plot of ln{-ln(1-

α)} against ln(t) gives a straight line with slope equal

to n and intercept equal to ln(k). The plots are shown

in Fig. 4(a-c) for the electrodeposition of copper in

different concentration of sulphuric acid and volume

percent of glycerol. The values of n and ln(k) are

given in Table 8.

Results and Discussion The apparent density of the powder decreases with

increasing percent of glycerol as well as sulpuric acid concentration. The increase of percent of glycerol and sulphuric acid concentration decrease formation dendrites in the powder. Therefore, the decrease in the apparent density may be considered a measure of decrease of dendrites in the powder. The Avrami-Erofeev n value is almost one and does not vary with percent of glycerol and sulphuric acid concentration. This is an indication that particles are of two dimensional in nature. The percent of glycerol between 10 to 15% and sulphuric acid concentration between 0.5 to 1.0N produce the powder, which contains more of square, hexagonal, cubical, and spherical shape particles and less of weakly bonded dendrites particles. When the rate of deposition of copper is slow this type of particles are produced as evident from chemical kinetics as well as the Avrami-Erofeev kinetics. Decrease in rate constant in both

Table 6―Morphology of copper powder and related data

Concentration

H2SO4 (N)+

glycerol ( %)

Apparen density

powder

Current efficiency Stability of powder % of particles

below 94.4 µm

Morphology of electrodeposited

powders(Size of nano-particle, nm)

0 + 7.5 5.3 67.5 64.9 79.6 Dendrites noticed and round or

spherical agglomerates (200-600)

0 + 15 3.1 74.5 74.0 86.0 Dendrites noticed and round or

spherical agglomerates (200-700)

0.5 + 10 3.2 76.0 77.1 87.3 Weakly bonded dendrites were

noticed. square, hexagonal and

spherical are found (200-600)

0.5 + 15 2.8 77.7 78.0 94.4 Weakly bonded dendrites were

noticed square, hexagonal and

spherical are found (200-700)

1.0 + 5 4.2 63 6 74.5 91.9 Almost cubical and hexagonal

(200-600)

1.0 + 10 2.2 84.2 74.6 91.2 spherical, hexagonal and cubical

(200-500)

Table 7―Reaction rate constants of the electrodeposition kinetics

H2SO4

concentration

Reaction rate constant (min-1)

(N) 2.5% 5% 7.5% 10% 15%

0.0 0.0095 0.0085 0.0078 0.0068 0.0066

0.5 0.0109 0.0095 0.009 0.0077 0.007

1.0 0.0118 0.01 0.0096 0.0081 0.0075

Table 8―Avrami-Erofeev kinetic constants

% Sulphuric acid concentration

glycerol 0.0 N 0.5 N 1.0 N

n ln(k) n ln(k) n ln(k)

2.5 1.121 -5.166 1.766 -4.824 1.209 -4.833

5.0 1.130 -4.985 1.153 -4.926 1.883 -5.022

7.5 1.066 -4.844 1.165 -5.005 1.151 -4.919

10 1.034 -4.900 1.116 -5.074 1.087 -4.891

15 1.047 -5.026 1.119 -5.217 1.069 -4.898

VISWANATH & GEORGE: ELECTROWINNING OF COPPER POWDER FROM COPPER SULPHATE SOLUTION

43

cases can be attributed to the decrease in the ion environment or ion strength due to the presence of glycerol molecules in the solution.

When the electrowinning process is completed the acid concentration reaches almost double the initial concentration of the acid. This increase of the acid strength is due formation of sulphuric acid from sulphate ions, different carboxylic acids by the electrolytic oxidation of glycerol molecules and elimination of water molecules from the solution by electrolysis.

During electrolysis all positive ions align and

migrate towards cathode while negative ions migrate

towards anode. The metal ion is discharged at the

cathode. The solid metal atoms so deposited on the

cathode should have a strong metallic bond. Since a

large amount of hydrogen liberated at cathode makes

the deposit porous and also the solution containing

Fig. 3―Plots of α against time in (a) different percent of glycerol,

(b) 1.0NH2SO4 and different percent of glycerol and (c)

1.5NH2SO4 and different percent of glycerol Fig. 4―Plots of ln(-ln(1- α)) against time in (a) different percent

of glycerol; (b) 1.0NH2SO4 and different percent of glycerol and

(c) 1.5NH2SO4 and different percent of glycerol.

(a)

(b)

(c)

(a)

(b)

(c)

INDIAN J CHEM. TECHNOL, JANUARY 2011

44

organic solvent which is covalent in nature disturbs

this ion environment particularly at cathode and

causes lose bonding between metal-metal atoms that

results in the formation of metallic powder.

The percent of glycerol between 10 to 15% and

sulphuric acid concentration 1.0N produce about 86%

particles having 74.75 µm and above 72% particles

having 54.1 microns. If the powder contains more of

square, hexagonal, and cubical shape particles, the

size of particles lies between 28 to 75 µm. Generally

spherical particles have smaller size because of strong

inter-atomic forces hold the particle together firmly.

Agglomerated particles and dendrites will have large

area so the particle size will be above 75 µm.

It is found that increasing in the percent of glycerol

and sulphuric acid concentration increases the

oxidative stability of powder. If the powder has larger

surface area, lesser is the oxidative stability of powder.

This may be due to the fact that more number of copper

atoms at the surface has free valances. In the present

case, the oxidative stability of powder is due to smaller

size of the particles having small surface area.

Conclusions It may be concluded that 10-15% of glycerol and

0.5-1.0 N sulphuric acid gives powder having good properties. Under these conditions nearly 95% copper powder has the particles whose size is below 95 µm, the powder is free from dendrites and stability of the powder is about 85%. The sulpuric acid is needed to

prevent the hydrolysis of copper ions. The applied current strength should not exceed 0.5 A. The large current densities warm the solution and the bath temperature increases as well as rate of deposing of the powder. So, lower rate of deposition is another important factor to get powder having good properties.

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