(2013) Behnamfard Probduction of Copper Cathode From Oxidized Copper Ores by Acidic Leaching And
Content
Hydrometallurgy 133 (2013) 111–117
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Hydrometallurgy
journal homepage: www.elsevier.com/locate/hydromet
Production of copper cathode from oxidized copper ores by acidic leaching and
two-step precipitation followed by electrowinning
Hossein Kamran Haghighi b,⁎, Davood Moradkhani a, Behzad Sedaghat c,
Majid Rajaie Najafabadi b, Ali Behnamfard b
a
b
c
Faculty of Engineering, Zanjan University, Zanjan, Iran
Department of Mining and Metallurgical Engineering, Amirkabir University of Technology, Tehran, Iran
Research and Engineering Company for Non-ferrous Metals (RECO), P.O. Box 45195-1445, Zanjan, Iran
a r t i c l e
i n f o
Article history:
Received 31 March 2012
Received in revised form 17 December 2012
Accepted 18 December 2012
Available online 23 December 2012
Keywords:
Acidic leaching
Sodium hydroxide
Precipitation
Copper cathode
Electrowinning
a b s t r a c t
A step by step hydrometallurgical process for the production of copper cathode was developed after a
two-step precipitation from leaching solution of copper oxidized ore, followed by copper concentrate
leaching and electrowinning. The copper oxidized ore was primarily comminuted to a size below 100 μ,
followed by acidic leaching at 25 °C for 40 min in H2SO4 solution, in which recovery of copper and iron
were 95.95% and 12.63%, respectively. To remove iron impurity, at the first step of precipitation, NaOH was
added to increase pH from about 1.5 to the optimum pH of 3.8 at 60 °C for 60 min; thus iron precipitation
with recovery of over 80% was achieved. Copper precipitate as concentrate was obtained in the same method
from iron-removed solution. The optimum condition of copper precipitation was found to be pH of 5.5, 25 °C
and 45 min with 98.69% recovery. One of the advantages of this process was production of Na2SO4 with 99.1%
purity after vaporization of the remaining solution from two-step precipitation. The obtained copper concentrate
was leached at approximately the same condition of the first leaching step, and then the provided pregnant
solution proceeded to an electrowinning cell with lead alloy anode contained antimony and steel sheet cathode
under the following condition: temperature of 50 °C, reaction voltage of 2 V and current density of 300 Am−2.
Finally, a scale-up experiment was carried out and the copper cathode with 99.99% purity produced.
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
The copper commonly produced from sulfide and oxide copper
ores is extracted through pyrometallurgical and hydrometallurgical
processes, respectively. In processing of oxide ores, the first step is
to leach ore by using a leaching agent commonly sulfuric acid. Several
studies have investigated the leaching of copper oxide ores with different types of acids (Habbache et al., 2009; Moradkhani et al., 2011). In
such processes, the major problem is the presence of iron in ore,
which comes to leach solution associated with copper ions. In order to
remove iron from leach solutions, several methods were applied
(Gudeczauskas and Natalie, 1985; Ismael and Carvalho, 2003; Nurmi
et al., 2010; Principe and Demopoulos, 2004; Wang et al., 2011). With
respect to the type of acid used in the leaching step, the pregnant solution proceeds to one of the following processes such as cementation, ion
exchange-electrowinning and or solvent extraction-electrowinning circuits (Bartos, 2002; Harris et al., 2007; Stefanowicz et al., 1997).
In this study, we developed a new systematic hydrometallurgical
process for the production of copper cathode from leaching solution
⁎ Corresponding author. Tel.: +98 9127431734.
E-mail address: [email protected] (H. Kamran Haghighi).
0304-386X/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.hydromet.2012.12.004
of copper concentrate obtained after leaching of copper oxidized ore,
two-step precipitation and copper concentrate leaching, followed by
electrowinning step. The remarkable feature of this process is the
production of some co-products such as Na2SO4. In this research, the
optimum condition of iron and copper precipitation from the leach
solution and electrodeposition of copper from the copper concentrate
leach solution were investigated. Finally, scale-up of the process was
conducted to reach the developed flowsheet.
2. Experimental methods
2.1. Materials and reagents
The investigation was carried out on a lean oxidized copper sample from Chodarchai Mine in Zanjan, Iran. The feed of leaching
obtained from mine ores was crushed and ground to a particle size
below 100μ. The feed was not exposed to any process. The composition of the oxide ore is presented in Table 1. The results of X-ray diffraction (XRD) analysis revealed that quartz is major phase and
malachite is minor phase. The results also indicated calcite, muscovite
and illite are present as trace phases. H2SO4 and NaOH were provided
by Merck Company.
112
H. Kamran Haghighi et al. / Hydrometallurgy 133 (2013) 111–117
Table 1
Chemical composition of copper oxide ore in the experiments.
Element
Cu
Fe
Zn
Pb
Ni
Cd
Mn
Co
As
Mg
Ca
S
Al
wt (%)
3.01
2.73
0.21
0.20
0.01
0.00
0.08
0.03
0.01
0.13
0.58
0.31
3.5
2.2. Leaching experiments
In this research the copper oxide and copper concentrate obtained
from copper precipitation step were leached. The leaching experiments were carried out in a flask with mechanical stirrer under the
following condition: H2SO4, 2 molar; leaching time, 40 min; at the
room temperature. The L:S ratio (v/w) for the leaching of copper
oxide and copper concentrate was conducted at 3.8:1 and 5:1, respectively. The concentration of copper was calculated with respect to
correction of volume (Choo et al., 2006).
2.3. Iron and copper precipitation experiments
A series of experiments designed by Response Surface Methodology
(RSM) was carried out to find the optimized time, pH and temperature
for the iron precipitation. Initially, 150 mL of the leach solution was
mixed and heated at different temperatures for various times and
simultaneously adjusted to a certain pH value using NaOH. At the end
of the experiments, the pulp was filtered, and the filtrates and the precipitates were separately analyzed for iron and copper.
After finding the optimized condition for the iron precipitation, a
series of experiments was run to find the effect of time, pH and temperature on the copper precipitation with NaOH. For this purpose,
after precipitation of iron at the optimized condition, 150 mL of the
iron-removed solution was used to investigate the effect of the
aforementioned parameters.
2.4. Electrowinning experiment
The copper solution achieved from the leaching of copper concentrate was used in electrowinnging experiments. The leach solution
with respect to the presence of returned spent in scale-up system was
diluted. Therefore, we employed an electrolyte containing Cu
54.13 g/L, Fe 1.1 g/L without other elements. A lead alloy anode
containing antimony and one stainless steel cathode in a reactor
containing 500 mL of the copper solution created the electrowinning
system. The areas of cathodes and anodes were 70 cm 2.
The electrolyte was slightly agitated with a magnetic stirrer (heater
stirrer model Yellow line, MST basic C). To supply current, a digital
laboratory DC power supply (MEGATEK, model MP-3005D) was
used. During electrolysis, the potential was adjusted by varying the
current manually. Finally, solid depositions on the cathodes were
Table 2
Concentration of elements in the leaching solution and the leaching rates.
Components
Concentration (mg/L)
Leaching (%)
Cu
Fe
Pb
Zn
Cd
Ni
Mn
As
Ba
Ca
Mg
Al
Co
Ce
Cl
7.600 (g/L)
1.000 (g/L)
10.150
166.910
0.960
1.410
0.090
3.000
0.300
0.490
0.000
9.160
0.500
0.290
1.740
95.947
12.625
0.128
2.107
0.012
0.018
0.001
0.038
0.004
0.006
0.000
0.116
0.006
0.004
0.022
stripped, washed with demineralized H2O, dried in the air, weighted
and analyzed. All electrowinning experiments were conducted at the
temperature of 40–60 °C, reaction voltage of 2 V and current density
of 200 Am − 2.
2.5. Chemical analysis
The concentrations of iron and copper in the solutions were analyzed by Perkin-Elmer AA300 model atomic absorption spectrophotometer. The cathode, precipitates and chemical composition of the copper
oxide ore were analyzed by XRF. Leaching toxicity extraction test of the
leaching residue was performed in accordance with Solid Waste Extraction Procedure for Leaching Toxicity – Horizontal Vibration Method
(China GB5086.2-1997 and US EPA Method 1311 TCLP test).
3. Results and Discussion
3.1. Leaching
The primary leaching test results are shown in Table 2. The leaching
rate of copper and iron are 95.95% and 12.63%, respectively. At this condition, copper and iron concentrations are 7.6 g/L and 1 g/L, respectively.
The extractions of the other elements Pb, Cd, Ni, Mn, As, Ba, Ca, Mg, Al, Co,
Ce and Cl are all less than 15 mg/L and for Zn is 166.91 mg/L. The effect of
operational parameters on the leaching has been investigated by
Moradkhani et al. (2011) and the results were published elsewhere.
The further leaching was carried out on the copper concentrate
obtained from copper precipitation step. At this stage, the leaching
rate of copper was 99%. The concentrations of copper and iron in
the leaching solution were 97.45 g/L and 1.98 g/L, respectively. This
solution is ready to be sent to the electrowinning cell. The impurities
of the electrolyte entered to the electrowinning cell are illustrated in
Table 3. As seen in this table, the impurities of the electrolyte are
lower compared to the copper electrowinning limitations.
3.2. Iron Precipitations
The effect of pH, temperature and reaction time on the iron precipitation recovery (RFe) was studied. The optimum condition of parameters and their interactions were investigated by RSM. The effect of pH
and temperature on iron precipitation recovery can be seen in Fig. 1a.
As seen in the figure, the recovery of iron precipitation increases with
increasing pH and no considerable change is observed by raising the
temperature. Moreover, Fig. 1b shows that the effect of pH on RFe is
Table 3
Composition of the electrolyte entered to EW cell.
Ref.
Electrowinning
limitations (mg/L)
Leaching test
(mg/L)
Elements
Habashi (1997)
–
2000
430
16000
340
3580
1
100
20–50
96180
1940
92
2.10
0.02
1.20
0.20
0.86
1.12
Cu
Fe
Zn
Ni
Sb
As
Sn
Bi
Cl
Davenport et al. (2000)
H. Kamran Haghighi et al. / Hydrometallurgy 133 (2013) 111–117
113
Fig. 1. (a) Effect of pH (A) and temperature, °C; (B) on iron precipitation recovery (RFe); (b) Effect of pH (A) and time, min (C) on iron precipitation recovery (RFe); i.e. Figures are
obtained from RSM, Design Expert 7 software.
Therefore:
similar to Fig. 1a; furthermore, with prolonging time the recovery of the
iron precipitation does not change considerably.
A 60 min reaction time, 60 °C temperature and pH of 3.80
obtained by RSM were used in the subsequent experiments as the
optimum condition. At this condition, the precipitation recovery of
iron is 82%. Obviously, over 80% of iron in the leaching solution
can be precipitated while the pH value rises to 3.8 by sodium
hydroxide.
Control of potential and pH is the most applied method of removing
impurities (Jackson, 1986). In precipitation processes, the critical factor
is to control pH, which should be increased from low pH values by
alkaline solution. Precipitation of iron from a leach solution by NaOH occurs according to Eq. (1).
3þ
Fe
þ
þ 3NaðOHÞ ¼ 3Na þ FeðOHÞ3
Ks ¼ α Fe3þ α
3
OH
If α Fe3þ ¼ 1 10
¼ 3:8 10
−5
−38
α
ð2Þ
ð3Þ
M
OH
¼
3:8 10−3S
1 10−5
ð4Þ
Where Ks is solubility product and αspecies is relative activity of species. Eqs. (2) to (4) indicate that pH 3.2 or pOH 10.8 is the starting point
of precipitation (Jackson, 1986). Therefore, when the pH rises to 3.2, ferric hydroxides start to precipitate. It should be noticed that the aforementioned pH value varies with iron ions activity and temperature.
The precipitation diagrams for metal hydroxides indicate the aforementioned thermodynamic data for any given activity. In addition, at the
iron precipitation pH, the precipitation of copper ions in the form of hydroxide occurs but due to low pH, its amount is negligible.
Fig. 2 illustrates the Fe-Cu-S-H2O system at 60 °C. Around the optimum pH of the iron precipitation (i.e., 3.8), Fe(OH)3 is dominant
species and precipitates in the form of Fe(OH)3. The type of iron precipitates is important with respect to the environmental protection
considerations. At this state according to the results, over 80% of
iron in the leaching solution precipitated.
ð1Þ
At 25BC
3
Eh (Volts)
2.0
1.5
Cu(+2a) Cu-Fe
1.0
Fe(OH)3
Fe2(SO4)3
Cu
Cu-Fe
0.5
Fe
Fe
0.0
Fe(+2a)
-0.5
SO4 (-2a)
CuSO4
Fe
Fe
Fe
Cu-Fe
H2O limits
Fe
Cu
Fe
Fe(OH2)
-1.0
Cu-Fe
S(-2a)
-1.5
-2.0
Fe2(SO4)3
Cu(+a)
0
2
4
6
8
10
12
14
pH
Fig. 2. Eh-pH diagrams of the system Cu–Fe–S–H2O. 60 °C, 1 bar, {Fe} = 0.02 M, {Cu} = 0.1 M, {S} = 1 M (HSC 5.1).
114
H. Kamran Haghighi et al. / Hydrometallurgy 133 (2013) 111–117
3.3. Copper Precipitation
The copper precipitation experiments to achieve the optimum results were classically carried out under the following conditions: pH
values of 5 to 7.5; temperatures of 25 to 80 °C for 5 to 60 min. At
the end of the experiments, according to the results, the optimum
condition of copper precipitation was found to be pH of 5.5, temperature of 25 °C for 45 min with recovery of 98.69%.
The copper can be precipitated from the iron-removed solution
using sodium hydroxide when the pH increases to approximately
5.5. As seen in Fig. 3, recovery of copper precipitate after the pH of
5 starts to rise up to the pH of 5.5 and subsequently descends to
the lower recoveries. In this figure, the maximum recovery of copper
precipitation is 98.69%. For copper ions, the calculations are done
similar to Eqs. (1) to (4). According to these equations, the precipitation
of copper hydroxide is approximately started at pH 5. Moreover, the
precipitation diagrams for metal hydroxides justify that the precipitation of copper hydroxide is approximately commenced at the pH 5. It
is noteworthy in these diagrams, at the higher pH values, the amount
of precipitation increases with respect to the lower values of solubility.
The effect of temperature on the copper precipitation is shown in
Fig. 4. As seen in the figure, the maximum copper precipitation is
achieved at 25 °C when the other factors are at their optimum condition.
The maximum recovery of copper precipitation at this temperature is
98.69%. This figure further illustrates that the high temperatures have inverse effect on the copper precipitation due to the following discussion.
Eq. (5) presents the reaction of copper precipitation:
CuSO4 þ 2NaOH→CuðOHÞ2 þ Na2 SO4
ð5Þ
In Eq. (5), ΔH of the reaction at 40 °C is − 50.550 (HSC 5.1), which
means the reaction is exothermic, thus with increasing temperature,
copper precipitation percentage falls down. The reaction time has
also an effect on the copper precipitation and grade (i.e., copper concentration in precipitate); yet in longer periods, it has no effect on the
copper precipitation (Fig. 5). The rates of copper precipitation and
grade respectively increase smoothly and intensively while the reaction time prolonged; however in longer periods, their rates are fixed.
According to this figure, the best condition is reaction time of 45 min
with copper precipitate grade of 49.2% and copper precipitation of
98.69%.
Fig. 4. Effect of the temperature on the copper precipitation (pH 5.5; time 45 min).
According to Eq. (6), when sodium hydroxide was added, around the
pH of 4 in which optimum condition achieved, y groups of OH- in
NaOH were directly situated by Fe3+ to form m groups of Fe(OH)3,
which has less solubility compared to other complexes in the solution.
The resistance time to form iron precipitation is 60 min, in which over
80 percent of iron is removed as solid phase. The following reaction is
proposed.
xFe2 ðSO4 Þ3 ðaqÞ þ yNaOHðaqÞ→mFeðOHÞ3 ðsÞ þ nNa2 ðSO4 ÞðaqÞ þ …
ð6Þ
In addition, according to Eq. (7), when adding NaOH proceeds, at
around pH of 5.5, k groups of OH - in NaOH were directly situated by
Cu 2+ to form p groups of Cu(OH)2, which has less solubility compared to other species in the solution. The following reaction is
suggested.
hCuðSO4 ÞðaqÞ þ kNaOHðaqÞ→pCuðOHÞ2 ðsÞ þ bNa2 ðSO4 ÞðaqÞ þ …
ð7Þ
As shown in Eqs. (6) and (7), after each precipitations, the amount
of Na2(SO4) majorly remained in the solution with the lowest impurities. This species can be considered as a co-product. Therefore, to attain this goal, vaporization of the solution at 90 °C was carried out. At
this state, the purity of Na2(SO4) is 99.1% that meets the industrial
standard.
3.5. Electrowinning
According to the aforementioned discussions, chemical reaction
taking place in the precipitation processes are proposed. The dominant forms of iron and copper in the liquor solution are CuSO4 and
Fe2(SO4)3. It is noteworthy that the other forms of species are also
present in the solution; however, the major reactions at the aforementioned pH values are accomplished by CuSO4 and Fe2(SO4)3.
The effective experimental parameters such as temperature, reaction voltage and current density in the electrowinning cell as the final
step were investigated. The electrowinning experiments were carried
out at temperature of 50 °C, reaction voltage of 2 V and current density of 300 Am −2 with the lead alloy anode contained antimony and
the steel sheet cathode as previously mentioned by Alfantazi and
Valic (2003). Under this condition, a copper cathode with 99.99% purity was obtained. Other components of the copper cathode have
been illustrated in Table 4, which shows that the quality of cathode
is acceptable.
Fig. 3. Effect of the pH on the copper precipitation (temperature 25 °C; time 45 min).
Fig. 5. Effect of time on the copper precipitation and grade (temperature 25 °C; pH 5.5).
3.4. Mechanism of Precipitation
H. Kamran Haghighi et al. / Hydrometallurgy 133 (2013) 111–117
extracting the desirable metal from it (Havlík, 2008). On the other
hand, the presence of H + ions in the solution produces an additional
cathodic reaction:
Table 4
Analytical composition of copper cathode.
Ba
As
Mn
Ni
Cd
Pb
Zn
Fe
Cu
Elements
0.01 0.3 0.001 0.7 0.1 1.2 0.9 3.1 99.99 Copper cathode (Present/
ppm)
þ
–
2H þ 2e ¼ H2 E0 ¼ 0V
If the anode does not dissolve, the electrons for precipitating of
copper must be achieved from an anodic reaction. They may be
substituted by ionization of water as Eq. (8):
þ
115
−
H2 →2H þ 1=2 O2 þ 2e E0 ¼ 1:23V
ð8Þ
Moreover, the release of oxygen is the result of this reaction.
Bonding between H + and SO42− anions is the cause of diffusion
through the electrolyte towards the anode and they regenerate the
acid called recycled acid for use in leaching or liquid extraction after
ð9Þ
Production of Eq. (9) releases gaseous hydrogen on the cathode.
Since the reaction of hydrogen release acts against precipitation of the
metal considering the available electrons, the amount of precipitated
metal by the transfer of the given amount of electrical energy decreases
with increasing the amount of released hydrogen. To precipitate copper
electrolytically, in the copper half-cell, the standard electrode potential
must be more positive for the release of hydrogen and at this condition,
copper precipitates preferentially from CuSO4 solution (Havlík, 2008).
To reduce the resistance of the electrolyte, it was heated to 50 °C. The
current density of the tests was practically in the range 100–500
Am –2. The anodes usually from lead alloys contain antimony and
Copper oxidized ore
Crushing and grinding
Water
Sulfuric acid
Acidic leaching for 60 min at 25oC
S
Leaching residue
L
Washing
Iron precipitation by increasing pH with
NaOH
Land fill
S
Iron filter cake
L
Sodium sulfate as a co-product
Evaporation
L
Bleed stream
Copper precipitation by increasing pH with
NaOH
S
Copper concentrate
Leaching by sulfuric acid
Returned spent (containing 40 g/l Cu)
Dissolved copper concentrate with approximate
grade of 3%
S
L
Copper electrowinning
Copper cathode (99.99%)
Fig. 6. Schematic flowsheet for the preparation of Cu concentrates from oxidized copper ores by acidic leaching, two-step precipitation and production of copper cathode with
99.99% purity.
116
H. Kamran Haghighi et al. / Hydrometallurgy 133 (2013) 111–117
Table 5
Scale-up experiment.
Materials
Composition of copper oxidized ore (%)
Primary leaching
Mass of material for scaling-up
Leaching condition
Volume of leaching solution
Concentration of elements in the leaching solution
Iron precipitation
Copper precipitation
Leaching on concentrate
Copper electrowinning
Copper leaching
rate (%)
Iron leaching rate (%)
condition
Volume of the filter after precipitation
Mass of the iron filter cake
Recovery of the iron precipitation
Copper loss percent
condition
Volume of the filter after precipitation
Grade of copper concentrate (%)
Grade of iron in copper concentrate (%)
concentrate of Na2SO4 as a co-product
Mass of the copper filter cake
Recovery of the copper precipitation
Copper loss percent (return to primary leach)
Mass of material for scaling-up
Leaching condition
Volume of leaching solution
Concentration of elements in the leaching solution
Copper leaching
rate (%)
Copper loss percent
Electrowinning condition
Volume of electrolyte
Electrodes
Concentration of elements in the cell electrolyte
Copper cathode grade
thin sheets of precipitated copper form the cathode sheets. In addition, to precipitate copper electrolytically, using steel sheets coated
with copper is common (Havlík, 2008). In this study, the aforementioned anode and cathode was used to electrowin.
3.6. Flowsheet for the production of copper cathode from copper oxidized
ore with co-product of Na2SO4
The integrated systematic process based on the aforementioned
results is presented in Fig. 6. The ore should be comminuted to smaller
than 100 μ before leaching. Mixing is necessary to speed up the leaching
process. After 45 min of leaching, the solid–liquid separation operation
is required. At this condition, the leach solution is at the pH of 1, pursued
by adding sodium hydroxide to precipitate iron in the leach solution. To
remove iron precipitates, separation between solid and liquid should be
performed. The precipitation of copper hydroxide can be carried out
from the iron-removed solution similar to the iron precipitation. After
the solid–liquid separation, the copper hydroxide concentrate can be
obtained. Moreover, to precipitate Na2SO4, the filtrated solution should
be vaporized at 90 °C. The purity of Na2SO4 is 99%, which meets the industrial standards.
The obtained copper concentrate with less iron impurity is ready
to proceed to the next step for leaching, followed by electrowinning
step. After filtering of the leaching solution, the obtained solution
goes to the electrowinning cell. A part of dissolved concentrates
remained on filters containing approximately 3% copper which
was returned to the primary leaching step. In the electrowinning
cell, two streams are entered to the cell. One stream is the leaching
solution and another is the returned spent solution containing
96.64 g/L and 40 g/L copper, respectively. The bleed stream is approximately 5–10% of electrowinning outlet flow, which returns to
Cu 3.01, Fe 2.73, Zn 0.21, Pb 0.20, Ni 0.01, Cd 0.00 Mn 0.08 Co 0.03,
As 0.01, Mg 0.13, Ca 0.58, S 0.31 Al 3.5.
3000 g of ores, 11.4 L water, H2SO4 6 molar.
25 °C, 60 min, pH of 1.
9.9 L
Cu 7.49 g/L, Fe 1.03 g/L, Zn 17 mg/L and other elements with the
concentrate less than 15 mg/L
94.56
13
pH of 3.80, 60 °C, 60 min
10.3
417
80%
7%
pH of 5.5, 25 °C, 45 min
9.5
49.2
1%
99%
160
98.5%
1.5%
2000 gram of concentrate with grade of 49.2%, 10 L water,
H2SO4 6 molar.
25 °C, 60 min, pH of 1
0.8 L
Cu 96.63 g/L, Fe 1.94 g/L without other elements
98.2
0%
temperature of 50 °C, reaction voltage of
2 V and current density of 200 Am−2
2L
anode of lead alloy contained antimony and steel sheet cathode
Cu 56.18 g/L, Fe 1.94 g/L
99.99%
the primary leaching step. Volume of the pregnant solution from
the copper concentrate leaching and the returned spent solution
are 0.8 and 2 L, respectively, which will result in an electrolyte
with the composition of Cu, 56.18 g/L and Fe, 1.94 g/L. At the end,
the copper cathode with 99.99% purity was obtained. With respect
to the loss of copper in each step, the total recovery of copper production process was equaled to 87.14%, which meets the economical
standard.
3.7. Scale-up experiments
To scale-up the process, 3000 g of lean oxidized ore from
Chodarchai mine in the Province of Zanjan, Iran was used. Process
properties, leaching, precipitation and electrowinning efficiencies
were obtained, as illustrated in Table 5. It illustrates that the leaching
rate of copper can reach 94.56%. After two-step precipitation, 80% of
iron is removed and around 98.5% of copper can be extracted from
the ore as the concentrate. Since the composition of the leaching solution, which mostly contains Cu, Cr, Bi, Ba, Cd, Ni, Hg, As, Pb and
Zn, is lower than the environmental limits, it is safe for the environment. In addition, the composition of the iron precipitate was environmentally safe in the iron precipitation step.
The primary leaching residue was washed with 6 molar H2SO4 solution and water. The results obtained by the toxicity characteristic
leaching procedure (TCLP) in Table 6 revealed that the obtained composition are lower than hazardous limits of the Maximum Concentration
of Contaminants for Toxicity Characteristic (United States Environmental Protection Agency and China GB/5085.3-2007). In addition, XRD
analyses indicate that the main phase composition of the primary
leaching residue is SiO2 and minor phases are orthoclase, kaolinite
H. Kamran Haghighi et al. / Hydrometallurgy 133 (2013) 111–117
117
References
Table 6
Leaching toxicity extraction test of the leaching residue.
Cu
Cr
Bi
Ba
Cd
Ni
Hg
As
Pb
Zn
Elements
58.23
0.05
0.01
3.25
0.35
0.10
0
0.27
1.07
25.20
100
5
0.02
100
1.0
5
0.2
5
5
100
Leaching test
(mg/L)
GB5085.3-2007
(mg/L)
and muscovite-illite. Therefore, the leaching residue can be identified as
the non-hazardous solid waste.
4. Conclusion
Leaching of Cu is carried out effectively in order to transfer Cu
from oxidized ore into H2SO4. To obtain copper concentrate from
leach solution, two precipitation steps with sodium hydroxide were
required. The copper recovery from the iron-removed solution reached
above 98% and the quality of copper concentrate met the industry standards. The copper and iron-removed solution contained Na2SO4 as a
co-product. Leaching of the copper concentrate provided the electrolyte
solution for electrowinning. In the electrowinning cell and at the optimum condition, the copper cathode with 99.99% purity was obtained.
Finally, a fully systematic hydrometallurgical process for the production
of copper cathodes from the electrolyte solution was developed.
Alfantazi, A.M., Valic, D., 2003. A study of copper electrowinning parameters using a
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Copper. Elsevier.
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leach liquors by ion exchange. Hydrometallurgy 14 (3), 369–385.
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New York, pp. 156–158.
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Contents lists available at SciVerse ScienceDirect
Hydrometallurgy
journal homepage: www.elsevier.com/locate/hydromet
Production of copper cathode from oxidized copper ores by acidic leaching and
two-step precipitation followed by electrowinning
Hossein Kamran Haghighi b,⁎, Davood Moradkhani a, Behzad Sedaghat c,
Majid Rajaie Najafabadi b, Ali Behnamfard b
a
b
c
Faculty of Engineering, Zanjan University, Zanjan, Iran
Department of Mining and Metallurgical Engineering, Amirkabir University of Technology, Tehran, Iran
Research and Engineering Company for Non-ferrous Metals (RECO), P.O. Box 45195-1445, Zanjan, Iran
a r t i c l e
i n f o
Article history:
Received 31 March 2012
Received in revised form 17 December 2012
Accepted 18 December 2012
Available online 23 December 2012
Keywords:
Acidic leaching
Sodium hydroxide
Precipitation
Copper cathode
Electrowinning
a b s t r a c t
A step by step hydrometallurgical process for the production of copper cathode was developed after a
two-step precipitation from leaching solution of copper oxidized ore, followed by copper concentrate
leaching and electrowinning. The copper oxidized ore was primarily comminuted to a size below 100 μ,
followed by acidic leaching at 25 °C for 40 min in H2SO4 solution, in which recovery of copper and iron
were 95.95% and 12.63%, respectively. To remove iron impurity, at the first step of precipitation, NaOH was
added to increase pH from about 1.5 to the optimum pH of 3.8 at 60 °C for 60 min; thus iron precipitation
with recovery of over 80% was achieved. Copper precipitate as concentrate was obtained in the same method
from iron-removed solution. The optimum condition of copper precipitation was found to be pH of 5.5, 25 °C
and 45 min with 98.69% recovery. One of the advantages of this process was production of Na2SO4 with 99.1%
purity after vaporization of the remaining solution from two-step precipitation. The obtained copper concentrate
was leached at approximately the same condition of the first leaching step, and then the provided pregnant
solution proceeded to an electrowinning cell with lead alloy anode contained antimony and steel sheet cathode
under the following condition: temperature of 50 °C, reaction voltage of 2 V and current density of 300 Am−2.
Finally, a scale-up experiment was carried out and the copper cathode with 99.99% purity produced.
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
The copper commonly produced from sulfide and oxide copper
ores is extracted through pyrometallurgical and hydrometallurgical
processes, respectively. In processing of oxide ores, the first step is
to leach ore by using a leaching agent commonly sulfuric acid. Several
studies have investigated the leaching of copper oxide ores with different types of acids (Habbache et al., 2009; Moradkhani et al., 2011). In
such processes, the major problem is the presence of iron in ore,
which comes to leach solution associated with copper ions. In order to
remove iron from leach solutions, several methods were applied
(Gudeczauskas and Natalie, 1985; Ismael and Carvalho, 2003; Nurmi
et al., 2010; Principe and Demopoulos, 2004; Wang et al., 2011). With
respect to the type of acid used in the leaching step, the pregnant solution proceeds to one of the following processes such as cementation, ion
exchange-electrowinning and or solvent extraction-electrowinning circuits (Bartos, 2002; Harris et al., 2007; Stefanowicz et al., 1997).
In this study, we developed a new systematic hydrometallurgical
process for the production of copper cathode from leaching solution
⁎ Corresponding author. Tel.: +98 9127431734.
E-mail address: [email protected] (H. Kamran Haghighi).
0304-386X/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.hydromet.2012.12.004
of copper concentrate obtained after leaching of copper oxidized ore,
two-step precipitation and copper concentrate leaching, followed by
electrowinning step. The remarkable feature of this process is the
production of some co-products such as Na2SO4. In this research, the
optimum condition of iron and copper precipitation from the leach
solution and electrodeposition of copper from the copper concentrate
leach solution were investigated. Finally, scale-up of the process was
conducted to reach the developed flowsheet.
2. Experimental methods
2.1. Materials and reagents
The investigation was carried out on a lean oxidized copper sample from Chodarchai Mine in Zanjan, Iran. The feed of leaching
obtained from mine ores was crushed and ground to a particle size
below 100μ. The feed was not exposed to any process. The composition of the oxide ore is presented in Table 1. The results of X-ray diffraction (XRD) analysis revealed that quartz is major phase and
malachite is minor phase. The results also indicated calcite, muscovite
and illite are present as trace phases. H2SO4 and NaOH were provided
by Merck Company.
112
H. Kamran Haghighi et al. / Hydrometallurgy 133 (2013) 111–117
Table 1
Chemical composition of copper oxide ore in the experiments.
Element
Cu
Fe
Zn
Pb
Ni
Cd
Mn
Co
As
Mg
Ca
S
Al
wt (%)
3.01
2.73
0.21
0.20
0.01
0.00
0.08
0.03
0.01
0.13
0.58
0.31
3.5
2.2. Leaching experiments
In this research the copper oxide and copper concentrate obtained
from copper precipitation step were leached. The leaching experiments were carried out in a flask with mechanical stirrer under the
following condition: H2SO4, 2 molar; leaching time, 40 min; at the
room temperature. The L:S ratio (v/w) for the leaching of copper
oxide and copper concentrate was conducted at 3.8:1 and 5:1, respectively. The concentration of copper was calculated with respect to
correction of volume (Choo et al., 2006).
2.3. Iron and copper precipitation experiments
A series of experiments designed by Response Surface Methodology
(RSM) was carried out to find the optimized time, pH and temperature
for the iron precipitation. Initially, 150 mL of the leach solution was
mixed and heated at different temperatures for various times and
simultaneously adjusted to a certain pH value using NaOH. At the end
of the experiments, the pulp was filtered, and the filtrates and the precipitates were separately analyzed for iron and copper.
After finding the optimized condition for the iron precipitation, a
series of experiments was run to find the effect of time, pH and temperature on the copper precipitation with NaOH. For this purpose,
after precipitation of iron at the optimized condition, 150 mL of the
iron-removed solution was used to investigate the effect of the
aforementioned parameters.
2.4. Electrowinning experiment
The copper solution achieved from the leaching of copper concentrate was used in electrowinnging experiments. The leach solution
with respect to the presence of returned spent in scale-up system was
diluted. Therefore, we employed an electrolyte containing Cu
54.13 g/L, Fe 1.1 g/L without other elements. A lead alloy anode
containing antimony and one stainless steel cathode in a reactor
containing 500 mL of the copper solution created the electrowinning
system. The areas of cathodes and anodes were 70 cm 2.
The electrolyte was slightly agitated with a magnetic stirrer (heater
stirrer model Yellow line, MST basic C). To supply current, a digital
laboratory DC power supply (MEGATEK, model MP-3005D) was
used. During electrolysis, the potential was adjusted by varying the
current manually. Finally, solid depositions on the cathodes were
Table 2
Concentration of elements in the leaching solution and the leaching rates.
Components
Concentration (mg/L)
Leaching (%)
Cu
Fe
Pb
Zn
Cd
Ni
Mn
As
Ba
Ca
Mg
Al
Co
Ce
Cl
7.600 (g/L)
1.000 (g/L)
10.150
166.910
0.960
1.410
0.090
3.000
0.300
0.490
0.000
9.160
0.500
0.290
1.740
95.947
12.625
0.128
2.107
0.012
0.018
0.001
0.038
0.004
0.006
0.000
0.116
0.006
0.004
0.022
stripped, washed with demineralized H2O, dried in the air, weighted
and analyzed. All electrowinning experiments were conducted at the
temperature of 40–60 °C, reaction voltage of 2 V and current density
of 200 Am − 2.
2.5. Chemical analysis
The concentrations of iron and copper in the solutions were analyzed by Perkin-Elmer AA300 model atomic absorption spectrophotometer. The cathode, precipitates and chemical composition of the copper
oxide ore were analyzed by XRF. Leaching toxicity extraction test of the
leaching residue was performed in accordance with Solid Waste Extraction Procedure for Leaching Toxicity – Horizontal Vibration Method
(China GB5086.2-1997 and US EPA Method 1311 TCLP test).
3. Results and Discussion
3.1. Leaching
The primary leaching test results are shown in Table 2. The leaching
rate of copper and iron are 95.95% and 12.63%, respectively. At this condition, copper and iron concentrations are 7.6 g/L and 1 g/L, respectively.
The extractions of the other elements Pb, Cd, Ni, Mn, As, Ba, Ca, Mg, Al, Co,
Ce and Cl are all less than 15 mg/L and for Zn is 166.91 mg/L. The effect of
operational parameters on the leaching has been investigated by
Moradkhani et al. (2011) and the results were published elsewhere.
The further leaching was carried out on the copper concentrate
obtained from copper precipitation step. At this stage, the leaching
rate of copper was 99%. The concentrations of copper and iron in
the leaching solution were 97.45 g/L and 1.98 g/L, respectively. This
solution is ready to be sent to the electrowinning cell. The impurities
of the electrolyte entered to the electrowinning cell are illustrated in
Table 3. As seen in this table, the impurities of the electrolyte are
lower compared to the copper electrowinning limitations.
3.2. Iron Precipitations
The effect of pH, temperature and reaction time on the iron precipitation recovery (RFe) was studied. The optimum condition of parameters and their interactions were investigated by RSM. The effect of pH
and temperature on iron precipitation recovery can be seen in Fig. 1a.
As seen in the figure, the recovery of iron precipitation increases with
increasing pH and no considerable change is observed by raising the
temperature. Moreover, Fig. 1b shows that the effect of pH on RFe is
Table 3
Composition of the electrolyte entered to EW cell.
Ref.
Electrowinning
limitations (mg/L)
Leaching test
(mg/L)
Elements
Habashi (1997)
–
2000
430
16000
340
3580
1
100
20–50
96180
1940
92
2.10
0.02
1.20
0.20
0.86
1.12
Cu
Fe
Zn
Ni
Sb
As
Sn
Bi
Cl
Davenport et al. (2000)
H. Kamran Haghighi et al. / Hydrometallurgy 133 (2013) 111–117
113
Fig. 1. (a) Effect of pH (A) and temperature, °C; (B) on iron precipitation recovery (RFe); (b) Effect of pH (A) and time, min (C) on iron precipitation recovery (RFe); i.e. Figures are
obtained from RSM, Design Expert 7 software.
Therefore:
similar to Fig. 1a; furthermore, with prolonging time the recovery of the
iron precipitation does not change considerably.
A 60 min reaction time, 60 °C temperature and pH of 3.80
obtained by RSM were used in the subsequent experiments as the
optimum condition. At this condition, the precipitation recovery of
iron is 82%. Obviously, over 80% of iron in the leaching solution
can be precipitated while the pH value rises to 3.8 by sodium
hydroxide.
Control of potential and pH is the most applied method of removing
impurities (Jackson, 1986). In precipitation processes, the critical factor
is to control pH, which should be increased from low pH values by
alkaline solution. Precipitation of iron from a leach solution by NaOH occurs according to Eq. (1).
3þ
Fe
þ
þ 3NaðOHÞ ¼ 3Na þ FeðOHÞ3
Ks ¼ α Fe3þ α
3
OH
If α Fe3þ ¼ 1 10
¼ 3:8 10
−5
−38
α
ð2Þ
ð3Þ
M
OH
¼
3:8 10−3S
1 10−5
ð4Þ
Where Ks is solubility product and αspecies is relative activity of species. Eqs. (2) to (4) indicate that pH 3.2 or pOH 10.8 is the starting point
of precipitation (Jackson, 1986). Therefore, when the pH rises to 3.2, ferric hydroxides start to precipitate. It should be noticed that the aforementioned pH value varies with iron ions activity and temperature.
The precipitation diagrams for metal hydroxides indicate the aforementioned thermodynamic data for any given activity. In addition, at the
iron precipitation pH, the precipitation of copper ions in the form of hydroxide occurs but due to low pH, its amount is negligible.
Fig. 2 illustrates the Fe-Cu-S-H2O system at 60 °C. Around the optimum pH of the iron precipitation (i.e., 3.8), Fe(OH)3 is dominant
species and precipitates in the form of Fe(OH)3. The type of iron precipitates is important with respect to the environmental protection
considerations. At this state according to the results, over 80% of
iron in the leaching solution precipitated.
ð1Þ
At 25BC
3
Eh (Volts)
2.0
1.5
Cu(+2a) Cu-Fe
1.0
Fe(OH)3
Fe2(SO4)3
Cu
Cu-Fe
0.5
Fe
Fe
0.0
Fe(+2a)
-0.5
SO4 (-2a)
CuSO4
Fe
Fe
Fe
Cu-Fe
H2O limits
Fe
Cu
Fe
Fe(OH2)
-1.0
Cu-Fe
S(-2a)
-1.5
-2.0
Fe2(SO4)3
Cu(+a)
0
2
4
6
8
10
12
14
pH
Fig. 2. Eh-pH diagrams of the system Cu–Fe–S–H2O. 60 °C, 1 bar, {Fe} = 0.02 M, {Cu} = 0.1 M, {S} = 1 M (HSC 5.1).
114
H. Kamran Haghighi et al. / Hydrometallurgy 133 (2013) 111–117
3.3. Copper Precipitation
The copper precipitation experiments to achieve the optimum results were classically carried out under the following conditions: pH
values of 5 to 7.5; temperatures of 25 to 80 °C for 5 to 60 min. At
the end of the experiments, according to the results, the optimum
condition of copper precipitation was found to be pH of 5.5, temperature of 25 °C for 45 min with recovery of 98.69%.
The copper can be precipitated from the iron-removed solution
using sodium hydroxide when the pH increases to approximately
5.5. As seen in Fig. 3, recovery of copper precipitate after the pH of
5 starts to rise up to the pH of 5.5 and subsequently descends to
the lower recoveries. In this figure, the maximum recovery of copper
precipitation is 98.69%. For copper ions, the calculations are done
similar to Eqs. (1) to (4). According to these equations, the precipitation
of copper hydroxide is approximately started at pH 5. Moreover, the
precipitation diagrams for metal hydroxides justify that the precipitation of copper hydroxide is approximately commenced at the pH 5. It
is noteworthy in these diagrams, at the higher pH values, the amount
of precipitation increases with respect to the lower values of solubility.
The effect of temperature on the copper precipitation is shown in
Fig. 4. As seen in the figure, the maximum copper precipitation is
achieved at 25 °C when the other factors are at their optimum condition.
The maximum recovery of copper precipitation at this temperature is
98.69%. This figure further illustrates that the high temperatures have inverse effect on the copper precipitation due to the following discussion.
Eq. (5) presents the reaction of copper precipitation:
CuSO4 þ 2NaOH→CuðOHÞ2 þ Na2 SO4
ð5Þ
In Eq. (5), ΔH of the reaction at 40 °C is − 50.550 (HSC 5.1), which
means the reaction is exothermic, thus with increasing temperature,
copper precipitation percentage falls down. The reaction time has
also an effect on the copper precipitation and grade (i.e., copper concentration in precipitate); yet in longer periods, it has no effect on the
copper precipitation (Fig. 5). The rates of copper precipitation and
grade respectively increase smoothly and intensively while the reaction time prolonged; however in longer periods, their rates are fixed.
According to this figure, the best condition is reaction time of 45 min
with copper precipitate grade of 49.2% and copper precipitation of
98.69%.
Fig. 4. Effect of the temperature on the copper precipitation (pH 5.5; time 45 min).
According to Eq. (6), when sodium hydroxide was added, around the
pH of 4 in which optimum condition achieved, y groups of OH- in
NaOH were directly situated by Fe3+ to form m groups of Fe(OH)3,
which has less solubility compared to other complexes in the solution.
The resistance time to form iron precipitation is 60 min, in which over
80 percent of iron is removed as solid phase. The following reaction is
proposed.
xFe2 ðSO4 Þ3 ðaqÞ þ yNaOHðaqÞ→mFeðOHÞ3 ðsÞ þ nNa2 ðSO4 ÞðaqÞ þ …
ð6Þ
In addition, according to Eq. (7), when adding NaOH proceeds, at
around pH of 5.5, k groups of OH - in NaOH were directly situated by
Cu 2+ to form p groups of Cu(OH)2, which has less solubility compared to other species in the solution. The following reaction is
suggested.
hCuðSO4 ÞðaqÞ þ kNaOHðaqÞ→pCuðOHÞ2 ðsÞ þ bNa2 ðSO4 ÞðaqÞ þ …
ð7Þ
As shown in Eqs. (6) and (7), after each precipitations, the amount
of Na2(SO4) majorly remained in the solution with the lowest impurities. This species can be considered as a co-product. Therefore, to attain this goal, vaporization of the solution at 90 °C was carried out. At
this state, the purity of Na2(SO4) is 99.1% that meets the industrial
standard.
3.5. Electrowinning
According to the aforementioned discussions, chemical reaction
taking place in the precipitation processes are proposed. The dominant forms of iron and copper in the liquor solution are CuSO4 and
Fe2(SO4)3. It is noteworthy that the other forms of species are also
present in the solution; however, the major reactions at the aforementioned pH values are accomplished by CuSO4 and Fe2(SO4)3.
The effective experimental parameters such as temperature, reaction voltage and current density in the electrowinning cell as the final
step were investigated. The electrowinning experiments were carried
out at temperature of 50 °C, reaction voltage of 2 V and current density of 300 Am −2 with the lead alloy anode contained antimony and
the steel sheet cathode as previously mentioned by Alfantazi and
Valic (2003). Under this condition, a copper cathode with 99.99% purity was obtained. Other components of the copper cathode have
been illustrated in Table 4, which shows that the quality of cathode
is acceptable.
Fig. 3. Effect of the pH on the copper precipitation (temperature 25 °C; time 45 min).
Fig. 5. Effect of time on the copper precipitation and grade (temperature 25 °C; pH 5.5).
3.4. Mechanism of Precipitation
H. Kamran Haghighi et al. / Hydrometallurgy 133 (2013) 111–117
extracting the desirable metal from it (Havlík, 2008). On the other
hand, the presence of H + ions in the solution produces an additional
cathodic reaction:
Table 4
Analytical composition of copper cathode.
Ba
As
Mn
Ni
Cd
Pb
Zn
Fe
Cu
Elements
0.01 0.3 0.001 0.7 0.1 1.2 0.9 3.1 99.99 Copper cathode (Present/
ppm)
þ
–
2H þ 2e ¼ H2 E0 ¼ 0V
If the anode does not dissolve, the electrons for precipitating of
copper must be achieved from an anodic reaction. They may be
substituted by ionization of water as Eq. (8):
þ
115
−
H2 →2H þ 1=2 O2 þ 2e E0 ¼ 1:23V
ð8Þ
Moreover, the release of oxygen is the result of this reaction.
Bonding between H + and SO42− anions is the cause of diffusion
through the electrolyte towards the anode and they regenerate the
acid called recycled acid for use in leaching or liquid extraction after
ð9Þ
Production of Eq. (9) releases gaseous hydrogen on the cathode.
Since the reaction of hydrogen release acts against precipitation of the
metal considering the available electrons, the amount of precipitated
metal by the transfer of the given amount of electrical energy decreases
with increasing the amount of released hydrogen. To precipitate copper
electrolytically, in the copper half-cell, the standard electrode potential
must be more positive for the release of hydrogen and at this condition,
copper precipitates preferentially from CuSO4 solution (Havlík, 2008).
To reduce the resistance of the electrolyte, it was heated to 50 °C. The
current density of the tests was practically in the range 100–500
Am –2. The anodes usually from lead alloys contain antimony and
Copper oxidized ore
Crushing and grinding
Water
Sulfuric acid
Acidic leaching for 60 min at 25oC
S
Leaching residue
L
Washing
Iron precipitation by increasing pH with
NaOH
Land fill
S
Iron filter cake
L
Sodium sulfate as a co-product
Evaporation
L
Bleed stream
Copper precipitation by increasing pH with
NaOH
S
Copper concentrate
Leaching by sulfuric acid
Returned spent (containing 40 g/l Cu)
Dissolved copper concentrate with approximate
grade of 3%
S
L
Copper electrowinning
Copper cathode (99.99%)
Fig. 6. Schematic flowsheet for the preparation of Cu concentrates from oxidized copper ores by acidic leaching, two-step precipitation and production of copper cathode with
99.99% purity.
116
H. Kamran Haghighi et al. / Hydrometallurgy 133 (2013) 111–117
Table 5
Scale-up experiment.
Materials
Composition of copper oxidized ore (%)
Primary leaching
Mass of material for scaling-up
Leaching condition
Volume of leaching solution
Concentration of elements in the leaching solution
Iron precipitation
Copper precipitation
Leaching on concentrate
Copper electrowinning
Copper leaching
rate (%)
Iron leaching rate (%)
condition
Volume of the filter after precipitation
Mass of the iron filter cake
Recovery of the iron precipitation
Copper loss percent
condition
Volume of the filter after precipitation
Grade of copper concentrate (%)
Grade of iron in copper concentrate (%)
concentrate of Na2SO4 as a co-product
Mass of the copper filter cake
Recovery of the copper precipitation
Copper loss percent (return to primary leach)
Mass of material for scaling-up
Leaching condition
Volume of leaching solution
Concentration of elements in the leaching solution
Copper leaching
rate (%)
Copper loss percent
Electrowinning condition
Volume of electrolyte
Electrodes
Concentration of elements in the cell electrolyte
Copper cathode grade
thin sheets of precipitated copper form the cathode sheets. In addition, to precipitate copper electrolytically, using steel sheets coated
with copper is common (Havlík, 2008). In this study, the aforementioned anode and cathode was used to electrowin.
3.6. Flowsheet for the production of copper cathode from copper oxidized
ore with co-product of Na2SO4
The integrated systematic process based on the aforementioned
results is presented in Fig. 6. The ore should be comminuted to smaller
than 100 μ before leaching. Mixing is necessary to speed up the leaching
process. After 45 min of leaching, the solid–liquid separation operation
is required. At this condition, the leach solution is at the pH of 1, pursued
by adding sodium hydroxide to precipitate iron in the leach solution. To
remove iron precipitates, separation between solid and liquid should be
performed. The precipitation of copper hydroxide can be carried out
from the iron-removed solution similar to the iron precipitation. After
the solid–liquid separation, the copper hydroxide concentrate can be
obtained. Moreover, to precipitate Na2SO4, the filtrated solution should
be vaporized at 90 °C. The purity of Na2SO4 is 99%, which meets the industrial standards.
The obtained copper concentrate with less iron impurity is ready
to proceed to the next step for leaching, followed by electrowinning
step. After filtering of the leaching solution, the obtained solution
goes to the electrowinning cell. A part of dissolved concentrates
remained on filters containing approximately 3% copper which
was returned to the primary leaching step. In the electrowinning
cell, two streams are entered to the cell. One stream is the leaching
solution and another is the returned spent solution containing
96.64 g/L and 40 g/L copper, respectively. The bleed stream is approximately 5–10% of electrowinning outlet flow, which returns to
Cu 3.01, Fe 2.73, Zn 0.21, Pb 0.20, Ni 0.01, Cd 0.00 Mn 0.08 Co 0.03,
As 0.01, Mg 0.13, Ca 0.58, S 0.31 Al 3.5.
3000 g of ores, 11.4 L water, H2SO4 6 molar.
25 °C, 60 min, pH of 1.
9.9 L
Cu 7.49 g/L, Fe 1.03 g/L, Zn 17 mg/L and other elements with the
concentrate less than 15 mg/L
94.56
13
pH of 3.80, 60 °C, 60 min
10.3
417
80%
7%
pH of 5.5, 25 °C, 45 min
9.5
49.2
1%
99%
160
98.5%
1.5%
2000 gram of concentrate with grade of 49.2%, 10 L water,
H2SO4 6 molar.
25 °C, 60 min, pH of 1
0.8 L
Cu 96.63 g/L, Fe 1.94 g/L without other elements
98.2
0%
temperature of 50 °C, reaction voltage of
2 V and current density of 200 Am−2
2L
anode of lead alloy contained antimony and steel sheet cathode
Cu 56.18 g/L, Fe 1.94 g/L
99.99%
the primary leaching step. Volume of the pregnant solution from
the copper concentrate leaching and the returned spent solution
are 0.8 and 2 L, respectively, which will result in an electrolyte
with the composition of Cu, 56.18 g/L and Fe, 1.94 g/L. At the end,
the copper cathode with 99.99% purity was obtained. With respect
to the loss of copper in each step, the total recovery of copper production process was equaled to 87.14%, which meets the economical
standard.
3.7. Scale-up experiments
To scale-up the process, 3000 g of lean oxidized ore from
Chodarchai mine in the Province of Zanjan, Iran was used. Process
properties, leaching, precipitation and electrowinning efficiencies
were obtained, as illustrated in Table 5. It illustrates that the leaching
rate of copper can reach 94.56%. After two-step precipitation, 80% of
iron is removed and around 98.5% of copper can be extracted from
the ore as the concentrate. Since the composition of the leaching solution, which mostly contains Cu, Cr, Bi, Ba, Cd, Ni, Hg, As, Pb and
Zn, is lower than the environmental limits, it is safe for the environment. In addition, the composition of the iron precipitate was environmentally safe in the iron precipitation step.
The primary leaching residue was washed with 6 molar H2SO4 solution and water. The results obtained by the toxicity characteristic
leaching procedure (TCLP) in Table 6 revealed that the obtained composition are lower than hazardous limits of the Maximum Concentration
of Contaminants for Toxicity Characteristic (United States Environmental Protection Agency and China GB/5085.3-2007). In addition, XRD
analyses indicate that the main phase composition of the primary
leaching residue is SiO2 and minor phases are orthoclase, kaolinite
H. Kamran Haghighi et al. / Hydrometallurgy 133 (2013) 111–117
117
References
Table 6
Leaching toxicity extraction test of the leaching residue.
Cu
Cr
Bi
Ba
Cd
Ni
Hg
As
Pb
Zn
Elements
58.23
0.05
0.01
3.25
0.35
0.10
0
0.27
1.07
25.20
100
5
0.02
100
1.0
5
0.2
5
5
100
Leaching test
(mg/L)
GB5085.3-2007
(mg/L)
and muscovite-illite. Therefore, the leaching residue can be identified as
the non-hazardous solid waste.
4. Conclusion
Leaching of Cu is carried out effectively in order to transfer Cu
from oxidized ore into H2SO4. To obtain copper concentrate from
leach solution, two precipitation steps with sodium hydroxide were
required. The copper recovery from the iron-removed solution reached
above 98% and the quality of copper concentrate met the industry standards. The copper and iron-removed solution contained Na2SO4 as a
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