dissolution kinetics of metallic copper with cuso4–nacl–hcl

8/9/2019 Dissolution Kinetics of Metallic Copper With CuSO4–NaCl–HCl

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Dissolution kinetics of metallic copper with CuSO4 –NaCl–HCl

Osvaldo Herrerosa,T, Roberto Quiroza , Ambrosio Restovic b, Joan Viñalsc

a Departamento Ingenierı́a Minas, Universidad de Antofagasta, Casilla 170, Antofagasta, Chile b Departamento de Quı́mica, Universidad de Antofagasta, Chile

c Departamento de Ingenierı́a Quı́mica y Metalurgia, Universidad de Barcelona, Spain

Received 4 May 2004; received in revised form 10 November 2004; accepted 21 November 2004

Abstract

A study was made on the dissolution kinetics of metallic copper flat packs using solutions of Cu(II) in a chloride medium

which was obtained via reaction between copper sulfate and sodium chloride. The effect of stirring, chloride and Cu(II)

concentrations, distribution of Cu(II) chlorocomplexes and temperature were investigated.

The leaching data showed the reaction to be under chemical kinetics control, with an activation energy of 28 kJ/mol (7 kcal/

mol). Leaching occurred at an apparent order of 1 with respect to the total chloride concentration and an apparent first order with respect to the total copper concentration. The Cu(II) ion was the main active species based on calculation of copper species

distribution and the solution kinetics may be interpreted as rate= k [Cu

2+

]. For ratios of C Cl/ C Cu2+

of less than about 8, a layer of CuCl(s) formed which impeded the solubilization process.

D 2005 Elsevier B.V. All rights reserved.

Keywords: Copper; Leaching; Chlorides; Chlorocomplexes

1. Introduction

Processes for the leaching of metallic copper in

chloride media have been based primarily on the

action of cupric copper in the presence of sodium

chloride. Important references on this topic include

the studies of Lin et al. (1992) and Tolley et al. (1977),

which report on the thermodynamics of the equili-

brium involved as well as on kinetic data in the Cu/

Cl system. Lin et al. report a copper leaching rate

consistent with the following expression:

rate ¼ k Cu2þ 1=2

Cl½ 2 ð1Þ

The order of this in reference to [Cu2+] is 0.5, which is

in agreement with that reported by Tolley et al.

(1977), who leached copper beads with CuCl2 in a

stirred reactor.

The study carried out by Herreros et al. (1999)

on the dissolution of copper flat packs by aqueous

Cl2/Cl media (0.5102 –1.9102 M Cl2, 0.5–1.4

M Cltot ), reported that the most significant effects

0304-386X/$ - see front matter D 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.hydromet.2004.11.010

T Corresponding author.

E-mail address: [email protected] (O. Herreros).

Hydrometallurgy 77 (2005) 183–190

www.elsevier.com/locate/hydromet


2/8

were those related to the concentrations of chlorine

and chloride, and that the aqueous chlorine was the

reagent that made possible the dissolution of the

copper, with chloride contributing a negative effect.

The chloride inhibited the dissolution, probably due

to the formation of a superficial layer of CuCl.

When working with excess chlorine, however, the

dissolution of this solid CuCl was increased. In this

case the kinetic control was affected by the transfer

of mass in the film, with activation energy of 18 kJ/

mol (4.3 kcal/mol). The apparent order of reaction

with respect to chlorine was 1.0 and 0.17 for thechloride.

On the other hand, the literature describes a process

for copper recovery from bronze scrap in which

leaching is obtained using 0.28 M CuCl2 and 4.8 M

NaCl at a temperature of 75 8C (Langer et al., 1977).

The CLEAR process, dating from the 1970s (Copper

Leach, Electrolysis and Regeneration) also uses cupric

chloride together with a solution of 4.4 M NaCl and 2.4

M KCl, although in this case, the objective was the

leaching of chalcopyrite (Atwood and Livingston,

1980).In contrast with results from the preceding brief

literature review, the objective of the present research

was to study the dissolution of metallic copper with

cupric chlorocomplexes generated in situ by reacting

copper sulfate with sodium chloride in a hydro-

chloric acid medium, and then determining if the

CuCl+ complex is the main active species in the

leaching of the metallic copper by having a

sufficiently oxidative potential for obtaining the

solubilization. This kinetic study may be applicable

in the leaching of copper precipitates, which in Chile

have varying degrees of surface oxidation, as well as

in treatment of discarded cathodes from the electro-

winning process.

Our study determined the effects of the stirring,

temperature, as well as the concentrations of total

Cu(II), total chloride, and copper chlorocomplexes for

postulating the possible controlling stage or stages of

the dissolution, and modeling a kinetic expression for

the leaching rate.

1.1. Criteria for the application of kinetic models

It is broadly recognized in the literature that in the

case of dissolution of pure species without formation

of insoluble products in surface layers, the only

controlling steps can be the mass transfer through

the fluid film and the specific chemical reaction

(Levenspiel, 1979; Sohn and Wadsworth, 1986). In

the case of leaching of Cu with Cu(II) in a Cl

medium, competition may exist between a bsolid Q

intermediate formed on the surface of the metallic

copper, probably CuCl, which would tend to dissolve,whereupon the leaching reagent would advance to the

reaction surface.

A diagram of the possible steps is presented as Fig.

1. The reactions of this process would be

Cu þ Cu2þ þ 2Cl ¼ 2CuClðsÞ ð2Þ

Cu þ CuClþ þ Cl ¼ 2CuClðsÞ ð3Þ

2CuClðsÞ þ 2Cl ¼ 2CuCl2 ð4Þ

Cu + CuCl+ + Cl- CuCl+

Cu2+

Cu + Cu2+ + 2Cl- 2 CuCl

CuCl + Cl- CuCl2-

Cu0 CuCl Cu2+ orCuCl+

2 CuCl

Fig. 1. Scheme of the possible steps in the leaching of metallic copper with Cu(II) in chloride media.

O. Herreros et al. / Hydrometallurgy 77 (2005) 183–190184


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The overall reaction from combining Eqs. 3 and 4 is:

Cu þ CuClþ þ 3Cl ¼ 2CuCl2 ð5Þ

Following data from tables of standar d potentials

(Software HSC Chemistry; Duby, 1977), the equili-

brium of Cu(II)–Cu(I) in chloride solutions is shown as

Cu2þ þ Cl þ e ¼ CuCl E 0 ¼ 0:538V ð6Þ

and the Cu(I)–Cu(0) reduction as:

CuCl þ e ¼ Cu þ Cl E 0 ¼ 0:137V ð7Þ

Using these data, the solution of copper by cupric

chloride may be written as:

Cu þ Cu2þ þ 2Cl ¼ 2CuCl ð8Þ

Reaction (8) has E cel=0.401 V and free energy of

formation=38.7 kJ/mol (9.25 kcal/mol).The cuprous chloride is only slightly soluble under

these standard conditions, but its solubility increases

with increase in the chloride concentration due to the

successive formation of CuCl2 and CuCl3

2 ion

complexes. Also, the solubility increases with temper-

ature (Jackson, 1986).

1.2. Kinetic model utilized

The geometry of the particles used to carry out the

present leaching experiments was of small flat-packs,

and the conversion model used is described below

(Levenspiel, 1979; Sohn and Wadsworth, 1986):

a ¼ 2bk r

qBe0C AO½

nt ð9Þ

or also

a ¼ k expt ð10Þ

and

k exp ¼ 2bk r

qBe0C AO½

n ð11Þ

where a=fraction reacted, k exp=experimental rate

constant (min1), t =time (min), b=stoichiometric

factor (mol solid dissolved/mol leaching reagent),

qB=molar density of solid (mol solid dm3), [C AO]=

molar concentration of leaching species in the bulk

solution, n=reaction order, k r =rate constant (cm

min1, for n=1) and e0=flat pack thickness (cm).

1.3. Distribution of chloride species

When chloride ion and cupric ion share an aqueous

system, the composition of the result ing solution is

governed by the following equilibria (Duby, 1977):

Cu2þ þ Cl ¼ CuClþ K 1 ¼ 100:46 ð12Þ

CuClþ þ Cl ¼ CuCl2 Aqð Þ K 2 ¼ 100:27 ð13Þ

CuCl2 Aqð Þ þ Cl ¼ CuCl3 K 3 ¼ 10

2:48 ð14Þ

CuCl3 þ Cl ¼ CuCl24 K 4 ¼ 10

2:30 ð15Þ

For determination of the different species of the

copper chlorocomplexes in the initial solution, the

following material balance is used:

C Cl ¼ Cl½ þ CuClþ½ þ 2 CuCl2 Aqð Þ

þ 3 CuCl3

þ 4 CuCl24

ð16Þ

and

C Cl ¼ C NaCl þ C HCl ð17Þ

C Cu ¼ Cu2þ

þ CuClþ½ þ CuCl2 Aqð Þ

þ CuCl3

þ CuCl24

ð18Þ

where C Cl , C NaCl, C HCl and C Cu are total concen-

trations (mol/L), and [i] are concentrations of the

different species. If C Cl and C Cu are known, the

concentrations of the remaining species are defined if

it is assumed that the activity coefficients are near unity.

According to values for the formation of chlor-

ocomplexes, the predominant species in this Cu2+/Cl

system are Cu2+, CuCl+ and CuCl2(Aq).

2. Materials and experimental procedure

2.1. Materials

Metallic copper of about 99.99% purity was used in

all experimentation. Copper flat packs of about 11mm and 0.105 mm in thickness cut from electrolytic

copper sheets were used in the kinetic experiments. The

O. Herreros et al. / Hydrometallurgy 77 (2005) 183–190 185


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reagents, copper sulfate pentahydrate, sodium chloride

and hydrochloric acid, were of analytical grade.

2.2. Reactor

A conventional leaching apparatus was used,

consisting of a 1200-cm3 triple-neck spherical glass

reactor submerged in a thermostatic bath, and fitted

with motor-driven stirring using a Teflon-coated

agitator (propeller of 5 cm diameter). The solution

potential was continuously measured with a platinum

electrode and a AgCl/Ag (KClsat ) reference electrode,

connected to a high impedance potentiometer. Tem-

perature was also continuously monitored and the

progress of reaction, copper concentrations and the pH were measured by removing samples for measure-

ment at specified times. The reactor was operated

under closed conditions.

2.3. Leaching reagent

The experiments were designed so that the

concentration of both the total chloride as well as

total cupric ion could be determined initially.

The solutions used in each experiment were

obtained by the following methods: a given volume

of distilled water was placed in the reactor, followed

by given masses of copper sulfate pentahydrate and

sodium chloride, and the pH was adjusted with

concentrated HCl to the desired value. The system

was then made up to 1000 cm3, and the initial

concentration of copper and pH were determined.

The kinetic experiments were initiated once the

solution was prepared. Here 2 g of copper flat packs

was added at t =0, and the progress of the leaching was

determined by taking 5-ml samples of the liquid for

copper analysis using atomic absorption spectrometry

(AA). Selected samples of attacked copper in the dif-ferent conditions were examined by SEM/EDS in order

to detect possible layers of solid reaction products.

3. Results and discussion

3.1. Effect of stirring

The effect of stirring on the dissolution kinetics of

the copper flat packs was carried out fixing the initial

concentration of C Cu at 1.38101 (M), C Cl at

1.43 (M) and temperature of 24 8C. Under these

experimental conditions and according to the dis-

tribution of species (Eqs. (13)–(19)), it was foundthat [Cl]=1.3 M, [Cu2+ ]=0.019 M, [CuCl+]=0.070

M, [CuCl2]=0.049 M, [CuCl3]=2.1 104 M and

[CuCl4]=1.4 106 M.

The experiment al results are presented graphi-

cally in Fig. 2. In Fig. 2 it is seen that the fraction

reacted, a, increases as the stirring increases,

becoming essentially constant at stirrings above

350 rpm, which ensure full particle suspension.

This suggests that chemical or electrochemical

reaction control dominates at high agitations levels.

No formation of CuCl(s) was observed in this set of experiments.

3.2. Effect of total copper concentration

Leaching experiments were carried out by varying

the initial copper concentration in the system to

determine the effect produced by this reactant on the

dissolution kinetics of the copper flat packs in order to

subsequently determine the apparent order of reaction

(350 rpm, 24 8C, C Cl=1.43 M). The calculated

distribution of species for these experimental con-

ditions is shown in Table 1.

Fig. 3 presents the experimental leaching results

in graphical form. Fig. 3 shows that the exper-

imental data fit the flat packs model well for up to

15–20 min of leaching. By linear regression of a

0

0.1

0.2

0.3 0.4

0.5

0.6

0.7

0 20 40 60 80

Time (min)

F r a c t i o n r e a c t e d

180 rpm 300 rpm

350 rpm 400 rpm

Fig. 2. Dissolution of copper flat packs over time as a function of

the stirring speed (24 8C, C Cu=1.38101 M, C Cl=1.43 M).



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vs. t , the experimental rate constant, k exp, is

obtained. Fig. 4 illustrates the rate constant in

relation to the total copper concentration, Cu2+,

CuCl+ and CuCl2. It can be seen that the reaction

rate increases in proportion to the total copper concentration. However, when the concentration of

chloride is maintained constant, an increase in the

total copper concentration brings an almost propor-

tional increase in concentrations of the various Cu

species present. At this stage, the active species

responsible for the dissolution of the copper cannot

be clearly resolved from this effect.

3.3. Effect of total chloride concentration

Leaching experiments were carried out varying the

initial chloride concentration of the system to deter-mine the effect produced by this reactant on the

dissolution kinetics of copper flat packs and to

determine the apparent order of reaction (350 rpm,

24 8C, C Cu=3.39102 M).The calculated distribu-

tion of species f or these experimental conditions is

shown in Table 2.

The experimental r esults of the leaching are shown

in graphic form in Fig. 5. Fig. 5 shows that the

experimental leaching data fit the flat-packs model

well up to a time of 15–20 min. Over longer time

periods, lowering of the total Cu2+ concentration, as

consequence of the reaction progress, produces

curvature of the plots. No formation of a CuCl layer

was observed in this set of experiments. The experi-

ment rate constant (k exp ) was obtained by considering

only the straight portion of the curve of linear

regression of a vs. t .

Fig. 6 shows the dependence of k exp on the

concentrations of Cl and C Cl. The apparent order

of the reaction for both C Cl and free chloride was

1.1, based on the linear regression data of Fig. 6.This dependency may be due to the fact that the

chloride ion shows a real (chemical or electro-

chemical) order of about 1, although this order may only be apparent, i.e., increase in the chloride

concentration may decrease the concentrations of

active oxidants.

Table 1

Calculated distribution of species as a function of the total copper

concentration

Cl total(M)

Cu total(M)

Cl

(M)Cu2+

(M)CuCl+

(M)CuCl2(M)

1.43 0.0352 1.386 0.0044 0.0176 0.013

1.43 0.0442 1.375 0.0056 0.0222 0.016

1.43 0.0641 1.351 0.0083 0.0323 0.024

1.43 0.0820 1.329 0.0108 0.0415 0.030

0

0.2

0.4

0.6

0.8

1

0 4020 60 80

Time (min)

F r a c t i o n r e a

c t e d

0.035 M 0.044 M 0.064 M 0.082 M

Fig. 3. Fraction reacted vs. time, as a function of total copper

concentration (350 RPM, 24 8C, C Cl=1.43M).

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

0 0.040.02 0.06 0.08 0.1

Copper species concentration (mole/L)

K e x p ( 1 / m i n )

Cu tot Cu2+ CuCl+

CuCl2

Fig. 4. Dependence of the k exp on the concentrations of Cu2+,

CuCl+, CuCl2 and C Cu.(350 rpm, 24 8C, C Cl=1.43 M).

Table 2

Calculated distribution of species as a function of total chloride

Cl total

(M)

Cu total

(M)

Cl

(M)

Cu2+

(M)

CuCl+

(M)

CuCl2(M)

0.56 0.034 0.53 0.0115 0.0175 0.0049

0.74 0.034 0.71 0.0089 0.0182 0.0068

0.91 0.034 0.87 0.0073 0.0182 0.0084

1.43 0.034 1.39 0.0043 0.0171 0.0126



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Fig. 7 shows the approximately proportional depend-

ence of the rate constant on the calculated Cu2+

concentration; the fact that the curve passes practi-

cally through the origin strongly suggests that Cu2+

may be the active species in the copper leaching.

On the other hand, similar plots of rate constant

with respect to the calculated CuCl+ and CuCl2concentrations do not show significant correlation.

Thus, the effect of chloride concentration on the

leaching kinetics should be only apparent, sincevariation of [Cl] markedly varies the distribution of

calculated Cu(II) species. Among these, the only one

that shows a significant effect is Cu2+, which propor-

tionally increases the reaction rate. Increases in the

concentrations of the other species do not lead to

significant changes in the reaction rate which lead tothe conclusion that the Cu2+ is the main active species

under these conditions. The rate for the investigated

interval is:

rate ¼ k C Cu

1 þ 100:46 Cl½ þ 100:46100:27 Cl½ 2 ð19Þ

3.4. Effect of temperature

Experimental results of the effect of temperature

on the dissolution kinetics of copper flat packs are presented in Fig. 8. The experimental constants

based on the data of Fig. 8 were obtained by linear

regression. An Arrhenius plot is presented in Fig. 9.

An activation energy of 28 kJ/mol (aprox. 7 kcal/

0

0.05

0.1

0.15

0.2

0.250.3

0.35

0.4

0.45

0.5

0 4020 60 80

Time (min)

F r a c t i o n r e a

c t e d

0.56 M 0.74 M 0.91 M 1.43 M

Fig. 5. Fraction reacted vs. time, as a function of C Cl (350 rpm, 24

8C, C Cu 3.4102 M).

1.8

1.9

2

2.1

2.2

2.3

2.4

-0.2 -0.1 0 0.1 0.2 0.

- log [i] (mole/L)

- l o g K ( m i n - 1 )

Cl total Cl-

Fig. 6. Dependence of k exp on the C Cl and Cl concentrations (350

rpm, 24 8C, C Cu=3.4102 M).

0

0.002

0.004

0.0060.008

0.01

0.012

0.014

0.016

0 0.0040.002 0.006 0.008 0.01 0.012

Cu2+ concentration (M)

K e x p ( 1 / m i n )

Fig. 7. Dependence of k exp as a function of the calculated Cu2+

concentration (350 rpm, 24 8C, C Cu=3.39102 M).

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 2010 30 40

Time (min)

F r a c t i o n

r e a c t e d

9°C 15°C 24°C 37°C 47°C

Fig. 8. Fraction reacted vs. time as a function of temperature: (350

rpm, C Cu 1.37101 M, C Cl 1.43 M).



7/8

mol) was obtained, which is indicative of chemical

or electrochemical reaction control.

4. Surface study

Copper surfaces attacked with different concen-

trations of Cu(II) and chloride were studied by

scanning electron microscopy (SEM) coupled by

energy dispersive microanalysis (EDS). Samples

were carbon coated. Observation was performed by

secondary electron signal and EDS spectra were

recorded at 20 kV. For ratios C Cl/ C CuN8, no

formation of CuCl(s) on the copper was found. Fig.

10 is an example of corrosion texture observed for this concentration ratio.

However, for ratios C Cl/ C Cub8, formation of

CuCl(s) was found on the surface. Fig. 11 shows the

surface of metallic copper attacked for 5 min by NaCl

0.56M, HCl 0.06 M and total Cu of 0.08 M. Here, a

continuous layer of tetrahedric crystals of CuCl is

observed. The attack was rapid at 0.08 M Cu but the

concentration of the Cl is not very high, and thus, the

dissolution of the CuCl is slow in this case. Fig. 12

shows t he corresponding EDS spectrum of CuCl from

Fig. 11.

Based on the kinetics results, the species distribu-

tion calculations and the surface studies, it is

0

1

2

3

4

5

6

7

3 3.83.4 4.2

1000/T (1/K)

- l n K e x p

( m i n - 1 )

Fig. 9. Arrhenius plot of the experimental rate constants (350 rpm,

C Cu 1.37101 M, C Cl 1.43 M).

Fig. 10. SEM image of metallic copper attacked by NaCl 1.43 M,

HCl 0.06 M and total Cu of 0.034 M.

Fig. 11. SEM image of metallic copper attacked by NaCl=0.56 M,

HCl 0.06 M and total Cu of 0.08 M.

X-RAY:Live:Real:

0 – 20 keV

keV 10.6 >

15s Preset: Remaining:20s

85s25% Dead

100s

< .4 5.480FS= 1K 33 ctsch 284=MEM1:CL 0.62 CU 0.08 5MIN

C

C

C

C

u

u

u

l

Fig. 12. EDS spectrum of the CuCl.



8/8

suggested that the dissolution of copper with Cu(II) in

chloride media occurs in the following steps:

CuðsÞ þ Cu2þ

ðaqÞ ¼ 2Cuþ

ðadsÞ ð20Þ

CuþðadsÞ þ 2ClðaqÞ ¼ CuCl

2 ð21Þ

With a high Cl/Cu(II) ratio, reaction (20) would be a

slow and overall controlling process. In contrast, at

low Cl/Cu(II) ratios, reaction (21) would not occur,

forming CuCl(s) in accordance with:

CuþðadsÞ þ ClðaqÞ ¼ CuClðsÞ ð22Þ

inhibiting the reaction. If the chloride concentration

reached zero, there would be no attack on the metalliccopper as experimentally shown when exposing the

copper flat packs to solutions of Cu2+ in the absence

of chloride. It is thus clear that chloride is necessary in

the leaching process, although high concentrations of

the chloride decrease the reaction rate. Species

distribution calculations suggest that this is due to

decreasing the concentration of the active Cu2+

species.

5. Conclusions

(1) The dissolution of metallic copper using solu-

tions of Cu(II) in Cl media is relatively

insensitive to stirring when the particles are well

suspended. The activation energy of the process

is 28 kJ/mol (7 kcal/mol) which suggests

chemical-type control.

(2) The leaching rate of copper has an apparent

order of 1 with respect to the total chlorideconcentration and an apparent order of unity (1)

with respect to the copper concentration.

(3) The correlation of rate constants with thecalculated distribution of copper species in

solution indicates that the Cu(II) ion is the main

active species. Within the interval studied, the

equation for the rate is:

rate ¼ k C Cu

1 þ 100:46 Cl½ þ 100:46100:27 Cl½ 2

(4) For total chloride/total copper ratios of approx-

imately less than 8, a layer of cuprous chloride is

formed on the copper surface, which inhibits the

leaching process.

Acknowledgements

The authors thank the National Fund for Scientific

and Technological Research (FONDECYT) for sup-

port of the present study (FONDECYT project no.

1030046). The support of the bServeis Cientı́fico-

Tècnics de la Universitat de Barcelona Q in the surface

studies is also gratefully acknowledged.

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dissolution kinetics of metallic copper with cuso4–nacl–hcl

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