ijct 18(1) 37-44.pdf
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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: [email protected])
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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