International Journal of Nonferrous Metallurgy, 2013, 2, 128-135
http://dx.doi.org/10.4236/ijnm.2013.24019 Published Online October 2013 (http://www.scirp.org/journal/ijnm)
Argentinean Copper Concentrates: Structural
Aspects and Thermal Behaviour
Vanesa Bazan1*, Elena Brandaleze2, Leandro Santini2, Pedro Sarquis3
1CONICET—Instituto de Investigaciones Mineras, Universidad Nacional de San Juan, San Juan, Argentina
2Metallurgical Department and Technology and Materials Develop Center, DEYTEMA-Universidad Tecnológica
Nacional, Facultad Regional de San Nicolás, Colón, Argentina
3Instituto de Investigaciones Mineras, Universidad Nacional de San Juan, San Juan, Argentina
Email: *firstname.lastname@example.org, email@example.com, firstname.lastname@example.org
Received July 4, 2013; revised August 5, 2013; accepted August 28, 2013
Copyright © 2013 Vanesa Bazan et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
In Argentina, there are many sources of copper concentrates. Some of them are currently in operation, while others are
in the exploration stage. All copper concentrates produced are exported to other countries for copper refinement and to
create various finished products. It is desirable that in the near future, these copper concentrates will be processed in an
Argentinean industrial plant. The aim of this paper was to present the results of a characterisation study carried out on
five different copper concentrate samples. The thermal decomposition of the copper concentrates was determined by
differential thermal analysis and thermogravimetry (DTA TG). The information was correlated with the chemical com-
position and the mineralogical phases of the samples identified by X-ray diffraction. A melting test at temperatures of
up to 1300˚C was performed to complete the study of the concentrate’s behaviour during heating. After the test, all of
the samples were observed by light and electronic scanning microscopy to identify the different phases generated under
Keywords: Copper Concentrates; Thermal Analysis; Pyrometallurgy; Mineral Phases
The copper market is undoubtedly one of the most im-
portant metallic markets in the world. This statement is
based on the significantly increased global demand for
this metal and its alloys in recent years.
Argentina has large reserves of copper ores and con-
stitutes a strong supplier of concentrates in our region
[1-4]. The ores selected for this study contain between
0.5% - 0.8% copper and are free of impurities such as Sb,
As, Te and Se. Currently, concentrates obtained by flota-
tion operations are exported to other countries to produce
final copper products such as wires, pipes and sheets .
It is important to promote the installation of a copper
pyrometallurgy plant in our country to allow for the abil-
ity to process concentrates and create final products for
Argentina´s domestic market. Copper industrial proc-
esses include melting, conversion and refining operations
. To design the pyrometallurgy process, it is necessary
to completely characterise the concentrates. Thus, it is
necessary to obtain information about the current phases
that exist in concentrate particles and the type of trans-
formations and reactions that occur under processing
Winkel et al.  described the importance of enhan-
cing the knowledge about the high-temperature behav-
iour of copper iron sulphides, as well as the volatile im-
purities they contain. This information is essential to de-
velop new processes of extractive metallurgy.
Thermal analysis techniques, such as differential ther-
mal analysis (DTA) and thermogravimetry (TG), repre-
sent important tools to determine the concentrates’ beha-
viour during the decomposition of copper iron sulphides
and sulphur volatilisation rates [8-12].
In this paper, information regarding the thermal be-
haviour of five samples of Argentinean copper concen-
trates is presented. The results obtained by DTA and TG
were correlated with information determined by X-ray
diffraction (XRD) and a microscopy study. Structural
analyses of the concentrate samples were performed after
the melting tests. The test products were examined by
electron microscopy (SEM), and the phases were identi-
fied by XRD. The authors describe the mechanisms, such
opyright © 2013 SciRes. IJNM
V. BAZAN ET AL. 129
as mass transport, which allow for the separation of me-
2. Materials and Methods
Five samples of copper concentrates obtained by Rou-
gher flotation were selected for this study. The copper
ores were obtained from sources located in northern Ar-
The concentrate characterisation was carried out. The
chemical composition of each sample was determined by
acid attack and atomic absorption spectrometry using a
Perkin Elmer AA110 instrument. The crystal phases
were identified by X-ray diffraction (XRD) at room tem-
perature using a Philips X’Pert diffractometer. The sul-
phide quantification was conducted by applying the
ASTM standard C25 .
A microscopy study performed using an Olympus
GX51 light microscope and applying a LECO IA32
analysis system, which allowed for the observation of the
types of particles and their morphological characteristics.
Another objective of this paper was to evaluate the
behaviour of the concentrates at high temperatures. To
obtain information about the reactions that occur during-
heating, melting tests were carried out at temperatures of
up to 1300˚C in air. Samples were melted in a porcelain
crucible using an electric furnace. All of the melted sam-
ples were prepared for microscopy observation. Their
structure was studied using light and scanning electron
microscopy (SEM). Finally, the results were correlated
with the DTA-TG results.
3.1. Chemical Composition
The chemical composition of the five concentrates sam-
ples is presented in Table 1.
3.2. Mineral Phases
The X-ray diffraction results provide information re-
garding the crystalline phases present in the five samples
studied. The major minerals present in the concentrates
were chalcopyrite (CuFeS2), pyrite (Cu2S) and iron sul-
phide (FeS). Nevertheless, other minerals such as iron
bisulphide (FeS2), geerite (Cu8S5), enargite (Cu3AsS4)
and dicopper zinc silicon tetrasulphide (Cu2Zn SiS4),
among others, were identified. However, sample E was
observed to contain a lower chalcopyrite content and
higher pyrite content. In sample B, geerite (Cu8S5), enar-
gite (Cu3AsS4) and dicopper zinc silicon tetrasulphide
(Cu2Zn SiS4) were identified, and in sample C, PbS was
identified. Traces of cassiterite (SnO2) were identified in
samples A and D. Figures 1-5 show the diffractograms
of all of the samples, specifically the principal peaks
corresponding to the crystal phases observed.
Table 1. Chemical composition of the copper concentrates samples.
Sample Cu% Fe% Ins% SiO2% R2O3% CaO% MgO% S% Al2O3%
A 16.9 32.1 2.76 1.64 53.12 0.15 0.08 37.6 8.78
B 22.3 31.4 1.70 0.88 51.58 0.18 0.08 35.2 8.25
C 18.4 31.5 1.64 1.04 52.96 0.14 0.05 37.8 9.43
D 14.6 33.1 2.52 1.28 55.06 0.11 0.07 38.9 9.35
E 18.1 35.3 2.04 0.52 59.36 0.13 0.05 33.3 10.59
Sample Sb ppm As ppm Se ppm Te ppm
A <50 52 <50 <30
B <50 68 <50 <30
C <50 48 <50 <30
D <50 35 <50 <30
E <50 49 <50 <30
Copyright © 2013 SciRes. IJNM
V. BAZAN ET AL.
Figure 1. Sample A diffractogram.
Figure 2. Sample B diffractogram.
Figure 3. Sample C diffractogram.
3.3. Thermal Analysis Tests
DTA and TG tests were carried out at a heating rate of
10˚C/s using a JENCK instrument. In this manner, the
mechanisms of oxidation during heating up to 1000˚C
were characterised for all of the copper concentrate sam-
ples. For each sample, the first exothermic peak tem-
perature, Tin, was determined. This temperature estab-
lishes the beginning of the oxidisation reaction. The
Figure 4. Sample D diffractogram.
Figure 5. Sample E diffractogram.
exothermic heat, Qex, was determined by the area below
the DTA curve. These values represent the total heat that
developed during all of the reactions. Both values are
very useful for understanding the flash-melting process
Figure 6 shows the DTA curves of the five samples.
The Tin and Qex values calculated by numerical integra-
tion are presented in Table 2. Notably, both values are
related to the oxygen content of the copper, which in this
case, are constant.
The thermogravimetric curves (TG) (Figure 7) allow
for the observation of mass changes and losses in the
concentrate samples during heating.
3.4. Melting Test
Samples of each copper concentrate were melted in por-
celain crucibles at 1200˚C at a heating rate of 5˚C/min in
air. The structure of the solidified product of each sample
was studied by light and scng electron microscopy anni
Copyright © 2013 SciRes. IJNM
V. BAZAN ET AL. 131
Figure 6. DTA curves of the five copper concentrates samples.
Figure 7. Thermogravimetric curves of the copper concentrates.
Table 2. Values of the initial
le Copper law (%) Tin (˚C) Qex (KJ/Kg)
oxidation temperature Tin,
exothermic heat Qex and the copper law of the concen-
A 16.86 309 ± 10 13880 ± 300
B 22.28 344 5185
C 18.38 340 7328
D 14.65 390 3254
E 18.03 415 12225
EM). In all cases, three different layers were recog-
ect to the bottom-layer
opper bands and globular
nised: a greyish layer with a fine dispersion of white par-
ticles (located in the bottom of the crucible), a white (in-
termediate) layer that contained a large number of den-
dritic crystals and extensive porosity and finally a top
grey layer composed of spherical and irregular white
particles. Figure 8 shows a vertical cross section of the
solidified layers in sample A.
particles of a larger size with resp
Notably, in the intermediate white layer, native copper
bands (Figure 9) and white dendrites were observed. A
higher proportion of native c
rticles was observed in sample B. In the grey top layer,
white crystals with different morphologies, irregular,
needle-shaped and dendritic, were observed.
In samples B, C, D and E, the bottom and top grey
layers were observed to be thicker than those in sample
A and to contain a low proportion of white particles.
However, in all of the samples, the intermediate white
layer was observed to contain metallic copper bands.
The phases were examined by SEM in the three layers.
Elemental mapping revealed the elemental distribution in
each layer. Table 3 shows the elemental distribution ob-
Copyright © 2013 SciRes. IJNM
V. BAZAN ET AL.
Figure 8. Three layers present in the structure of solidified
m grey layer of the samples contains white
articles of silicoaluminate. A few particles of CuS and
on contents were observed near the
hologies). Traces of K, Ti and Cr were
ition of the concentrates show that
ed a higher Cu content (22.28%) and a
Fe (31.40%). Importantly, sample B
served in sample A.
phases with higher ir
terface in contact with the intermediate white layer.
Also, traces of other elements such as Mg and Cr in the
silicoaluminate matrix were detected.
The intermediate white layer contains metallic copper
bands, white dendrites or irregular crystals of (Cu, Fe)S,
and the matrix has a high iron sulphide (
The white and the grey top layers were observed to be
porous. Sample D showed the highest porosity among the
The top grey layer matrix consists of calcium sili-
coaluminate and copper sulphide particles (with dendritic
and globular morp
entified. Irregular copper particles isolated in the layer
and in the microcracks were also observed.
If we consider copper, iron and sulphur to be the main
elements and approximate their content to be 100%, it is
possible to plot on a ternary diagram the s
sition identified in the intermediate white layer and in
the grey top layer. For simplicity, the plotted composi-
tions correspond to samples A and D (Figure 10).
These two samples were selected because of the
phases differences observed. Samples B, C and E contain
phases similar to those observed in sample A but in
rent proportions. Notably, the sulphide phases devel-
oped under the test conditions (1200˚C) show copper
contents up to 52%.
The chemical compos
sample B possess
lower content of
also exhibited the lowest S/Cu ratio (1, 58).
Figure 9. Copper band observed in the intermediate.
Sample D contained the lowest concentration of Cu
oreover, the S/Cu ratio of sample D was 2.65, which is
u(X)) can be modelled by third-degree
.65%) and the highest S and Fe concentration
ghest value observed in the concentrate samples. The
XRD results are consistent with the chemical composi-
Based on the DTA results, the correlation between the
Tin and Qex values with respect to the law of copper con-
lynomial equations, (Equations (1) and (2)) for which
R = 0.9946.
TC1.425 X78.488 X
268157 X2 E
The Tin values vary with mineralogical com
and respect the following order of the samples:
B < D < E. As observed experimentally, sample B has an
cant loss of mass during heating between room
A < C <
termediate initial oxidation temperature. A higher con-
tent of pyrite indicates an increase in Tin because of the
high melting temperature of the compound. Nevertheless,
the other phases in the concentrates also affect Tin.
The exothermic heat Qex values were obtained by the
numerical integration of the exothermic peaks on the
DTA curves (Figure 6). The exothermic heat is gen
sociated with the oxygen content present during the
test. However, in this case, the oxygen concentration is
constant. Thus, it is possible that the higher value is due
to the chalcopyrite (CuFeS2) and coveline (CuS) con-
The DTA and TG curves show that the sample-B reac-
tions develop with low Qex, which is associated with a
mperature and 1000˚C. A gradual weight loss in the
Copyright © 2013 SciRes. IJNM
V. BAZAN ET AL.
Copyright © 2013 SciRes. IJNM
Table 3. Element distribution in the the layers of the post melted sampe A.
y layer Intermidiate white layer Top
Figure 10. Sulphide composition determined in the white (B)
intermediate layer and in the grey (G) top layer of sample
00˚C to 450˚C was observed for all of the con-
entrates. This change is attributed to humidity loss. In
entrate samples. The transformation of
formations are probably associated with the sulphide and
m HSC (Outokumpu), are detailed in
the chalcopyrite (CuFeS) transformation
se in mass determined by the TG
A and D.
range of 3
particular, sample E exhibited a drastic loss of mass at
500˚C; this is because the range 450˚C - 550˚C favours
the direct oxidation of pyre to loadstone, while at tem-
peratures above 650˚C the complete elimination of any
formed ferrous sulphate is favoured; this is manifested as
weight loss .
A gradual increase in mass up to 600˚C was observed
for all of the conc
e sulphides into oxides coincides with these mass-
change exothermic peaks (in DTA curves). A new and
pronounced loss of mass up to 750˚C was observed for
the five concentrates. At these temperatures, the trans-
The proposed reaction mechanisms, based on the be-
haviour indicated by the DTA and TG curves and the
equilibrium information obtained by calculation using
the software progra
The DTA results are consistent with proposed reaction
5, which implies a loss of mass because of the sul-
phide-to-oxide transformation. In addition, it is important
eactions 3 and 4).
The initial mass loss revealed by TG is based on the
decomposition of a pure Cu2S sample and the oxidation
of pyrite, as observed in reactions 5 and 6.
The gradual increa
st at 600˚C was also reported by Perez-Tello et al. .
They believed that the concentrates quickly gain mass
through the copper sulphate formation. Howev
shows that reactions 11 and 10 contribute to the in-
crease in mass through the formation of iron sulphide.
Although this species is later dissociated, as indicated by
reaction 14, the reaction speed is slow due to that the
formation of sulphates, which closes the pores of the
particle and prevents the reaction from occurring, and
thus creates a gain in mass, as shown in Figure 7 .
The gradual final loss of mass is explained by the de-
composition reactions of the sulphate into oxides.
Samples B and C showed the same behaviour during
heating because of their similar mineralogical compos
n: high content of chalcopyrite (CuFeS2) and low
copper and iron sulphides in the concentrate. Thes
es developed intermediate Tin and Qex during heating.
Sample A presented a lower Tin and higher Qex be-
cause of the higher contents of chalcopyrite (CuFeS2)
V. BAZAN ET AL.
Table 4. React
Mass changes % Reaction number −∆G˚ (kcal)reacc
5CuFeS2 + 9O2 (g) = Cu5FeS4 + 2Fe2O3 + 6SO2 −10.50 1
(g) 653 − 621
2Cu5FeS4 + 14.5O2 (g + Fe2O3 + 8SO2 (g)
2Cu5FeS4 + Fe2O3 1
2CuFeS 2(SO4)3 5
2FeSO O2 (g)
Fe2(SO4 5O2 (g)
) = 10CuO876 − 788 −4.85 2
2CuFeS2 + 6.5O2 (g) = 2CuO + Fe2O3 + 4SO2 (g) 436 − 406 −8.59 3
2CuFeS2 + 6O2 (g) = Cu2O + Fe2O3 + 4SO2 (g) 410 − 387 −17.50 4
2FeS2 + 5.5O2 (g) = Fe2O3 + 4SO 2 (g) 388 − 377 −33.44 5
2FeS + 3.5O2 (g) = Fe2O3 + 2SO2 (g) 273 − 253 −9.17 6
Cu2S + 2O2 (g) = 2CuO + SO2 (g) 113 − 98 −0.04 7
Cu2S + 1.5O2 (g) = Cu2O + SO2 (g) 86 − 79 −10.09 8
+ 2SO2 (g) + 19.5O2 (g) = 10CuSO4066 − 781 74.91 9
2 + 9O2 (g) + SO2 (g) = 2CuSO4 + Fe32 − 403 95.92 10
FeS2 + 3O2 (g) = FeSO4 + SO2 (g) 203 − 176 233.33 11
Cu2S + 2.5O2 (g) = CuO * CuSO4 125 − 90.61 50.26 12
2Cu2O + O2 (g) = 4CuO 14 − 5 11.17 13
4 + 1.5O2 (g) = Fe2O3 + 2SO2 (g) + 26 − 26 −47.44 14
)3 = Fe2O3 + 3SO2 (g) + 1.3 − 41 −60.06 15
2CuSO4 + O2 (g) = 2CuO + 2SO2 (g) + 2O2 (g) 10 − 14 −50.16 16
CuO * CuSO4 = 4CuO + 2SO2 (g) + O2 (g) 13 − 10 −33.48 17
Figure 11. Mass evolution with respect to reaction mecha-
n sulphide (FeS), promoting an intermediate
hange in weight.
bination of higher Qex and Tin. The
les showed that the contents of chalcopyrite
In the top grey layer matrix, white dendrites or irregu-
observed in the greatest quantity in samples D and
d AG or
at these materials
% to 22% copper and that sample B
copper. The major copper minerals
Sample E, which contained the highest percentage of
FeS, showed a com
ass lost by this sample is lower than that by samples A,
B and C.
The microscopy study of the five concentrates solidi-
d iron sulphide (i.e., sample A) in the concentrates
increase with the thickness of the white layer. In all sam-
ples, this white intermediate layer featured native copper
bands or globular particles because of the decomposition
of sulphides. In this case, the (Cu, Fe)S exhibited 31%
lar crystals of (Cu, Fe)S in a matrix with a higher iron
sulphide (FeS) content were identified. These phases
(Cu, Fe)S contained approximately 52% Cu.
Based on the S-Cu-Fe system, it was possible to con-
clude that different sulphide phases formed at the se-
lected melting test conditions (1200˚C, 1 h) in both lay-
ers (AB or DB in the white intermediate layer an
G of the grey top layer) contain up to 52% copper.
Chalcopyrite decomposes at 623 K to an intermediate
solid solution (ISS) (see Figure 10) or to chalcopyrite
with a slightly different composition (CuFeS2ssb); more-
over, an iron sulphide transformation occurred. The
presence of native copper in all of the samples indicates
that sulphur was only partly removed.
To summarise, the characterisation of the five concen-
trates studied in this work revealed th
contained about 14
was the richest in
were sulphides: chalcopyrite (CuFeS2) and coveline
(CuS). Iron was present in the concentrates in the form of
FeS2 or FeS. Samples A and E showed the highest iron
The thermal analysis techniques applied in this study
provided information that allowed us to determine the
Copyright © 2013 SciRes. IJNM
V. BAZAN ET AL. 135
initial oxidation temperature Tin and the exothermic heat
Qex of the samples, as well as the mass changes during
rogram HSC (Outokumpu), it was
Secretaria de Minería de la Nación. Buenos Aires, Argen-
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zan, “Algunos Fundamentos de las
P. Sarquis and E. Brandaleze, “Factibilidad
ating to 1000˚C.
By correlating the DTA and TG results with the crystal
phases identified by XRD and the information obtained
though the thermodynamic equilibrium study performed
using the software p
ssible to identify the complex reaction mechanisms
involved during concentrate heating. The reaction evolu-
tion features an initial transformation of the sulphides to
oxides; then, the oxides react to form sulphates and are
finally transformed to oxides. These results were con-
firmed by the phases identified by microscopy and the
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