Materials Transactions, Vol. 45, No. 9 (2004) pp. 2851 to 2856
#2004 The Japan Institute of Metals
Phase Relations and Distribution of Some Minor Elements
in Cu-Fe-As System Saturated with Carbon at 1473 K
Leandro Voisin, Hector M. Henao and Kimio Itagaki
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan
As a fundamental study to develop a new process for eliminating detrimental elements and for recovering valuable ones from secondary
Cu-Fe base alloys with a considerably high content of arsenic, both the phase relations in a miscibility gap of the Cu-Fe-As system saturated with
carbon and the distribution of some minor elements of silver, platinum, cobalt, nickel and sulfur between two phases in the miscibility gap were
investigated at 1473 K by using a quenching method. The phase separation into copper-rich and iron-rich phases occurred when the Cu-Fe-As
system was saturated with carbon. The arsenic content in the copper-rich phase was larger than that in the iron-rich phase, and carbon mostly
distributed in the iron-rich phase. Cobalt and nickel distributed preferentially in the iron-rich phase, and platinum and sulfur distributed almost
evenly in both phases, while silver mostly in the copper-rich phase. The experimental results for the phase separation and the distribution of the
minor elements were discussed on the basis of activity coefficients in the copper-rich and iron-rich phases. By utilizing this phase separation,
recovery of valuable silver and copper into the copper-rich phase and elimination of less valuable iron into the iron-rich phase are feasible for
treating the secondary Cu-Fe-As base alloys.
(Received May 26, 2004; Accepted July 8, 2004)
Keywords: phase relations, miscibility gap, distribution ratio, copper-iron-arsenic, secondary alloy, speiss, minor element, by-product
treatment
2.
Experimental Method and Procedure
The quenching method combined with the metallographic
method, combustion-infrared spectrometry for carbon, electron probe micro analysis (EPMA) and inductively coupled
plasma spectrometry (ICP) was used to determine the phase
relations and the distribution of the minor elements.
2.1 Phase relations in Fe-As-C ternary system
The phase relations in the Fe-As-C system were determined at 1473 K as stated later in this work. The system, as
shown in Fig. 1, was divided into two experimental zones or
pseudo ternary systems: the zone A or Fe-C-D and the zone B
or D-C-As pseudo ternary systems, where D corresponds to
C
0.6
0.4
NC
Sulfide ores containing bituminous coal reserves sometimes constitute a feed for copper smelting.1,2) The presence
of coal in a shaft furnace makes iron excessively dissolved in
the melt. In a ladle adjacent to the furnace, an iron base alloy
containing a considerable amount of arsenic solidifies and
accumulates as a furnace residue, which is generally called
‘‘speiss’’. Several other metals such as copper, cobalt, nickel,
silver, gold and platinum are dissolved in the residue and the
recovery of these valuable metals has offered a challenging
subject. In recent years, the content of arsenic in the sulfide
concentrates of non-ferrous metals tends to rise. This results
in the formation of matte, slag and flue dust or dross with a
considerably high content of arsenic in the nonferrous
smelting processes. The speiss may be also made when these
intermediate products are treated in a strongly reducing
condition where the metallic iron is formed. Therefore, the
behaviour of arsenic and valuable metals in the speiss is of
importance for treating the sulfide concentrates and byproducts with the high content of arsenic.
The Cu-Fe-As ternary system is a base for the speiss phase
related to the production of copper and the treatment of byproducts. According to a literature, the Cu-Fe system
saturated with carbon3) makes a miscibility gap at considerably low temperatures of less than 1500 K, which is
composed of the liquid copper phase with very small contents
of iron and carbon, and the liquid Fe-C alloy with about
7 mass% copper. This phase separation will be useful for
developing a new recovery process to treat the Cu-Fe-As base
speiss, in which the less valuable iron is to be removed into
the iron-rich phase, while the valuable copper and other
metals are enriched in the copper-rich phase.
Information on the phase relations and the distribution of
minor elements in the miscibility gap of the Cu-Fe-As system
saturated with carbon is of very importance for the process
development. Nevertheless, no data have been reported on
this system though the Cu-Fe-As ternary system4) and the CuFe-As-S quaternary system5) were studied by one of the
authors. Hence, in this study, the phase relations and the
distribution of some minor elements such as silver, platinum,
cobalt, nickel and sulfur in the region of miscibility gap of the
Cu-Fe-As system saturated with carbon were investigated at
1473 K by a quenching method. As a part of this quaternary
system, the Fe-As-C ternary system was also investigated.
Fe
Introduction
N
1.
0.8
Zone
Zone
A
B
Charge composition
Present work
0.2
Massalski 6)
Massalski 7)
Fe
Fig. 1
D
0.2
0.4
0.6
0.8
N As
Phase relations in the Fe-As-C ternary system at 1473 K.
As
2852
L. Voisin, H. M. Henao and K. Itagaki
the saturation point of iron with a mole fraction of arsenic,
NAs ¼ 0:15.6) For the experimental zone A, the samples were
prepared with pig iron and Fe2 As with the compositions close
to the liquidus line, which was anticipated from the
constituted binary diagrams.6,7) For the experimental zone
B, the samples were prepared with different ratios between
iron and Fe2 As. In both zones, 5 g of sample together with a
graphite rod was charged in a MgO crucible and then vacuum
sealed in a quartz ampoule. The starting Fe2 As (melting
point: 1203 K6)) was synthesized with iron and arsenic
(99.99% purity) in a quartz ampoule by a thermal treatment.
The ternary alloy sample was heated and kept at 1473 K for
43.2 ks and then quenched into water. It was confirmed in a
preliminary experiment that the equilibration between the
coexisting phases was made in 43.2 ks.
2.2
Phase relations in miscibility gap of Cu-Fe-As-C
system
5 g of sample was prepared by proportionally mixing the
pure elements of Fe and Cu with Fe2 As and Cu3 As according
to the required charge composition in the Cu-Fe-As system
saturated with carbon. Cu3 As (melting point: 1100 K6)) was
synthesized with copper and arsenic (99.99% purity) by a
thermal treatment. The ratio of mass% Cu to mass% Fe in the
total charge, MCu =MFe , were fixed at 1/3, 1/1 and 3/1. The
sample together with a graphite rod was charged in a MgO
crucible, and then vacuum sealed in a quartz ampoule of
0.09 m length and 0.026 m ID. The ampoule was heated and
kept at 1473 K for 43.2 ks to establish the equilibrium
between the two phases in the miscibility gap, and then it was
quenched into water. The solidified sample was examined by
the metallographic analysis and EPMA to confirm the
presence of two clearly separated immiscible phases. Once
this was confirmed, the two phases were separated with a
cutter and representative samples were taken for each phase
and later on analyzed for their components.
Table 1
1/3
1/1
3/1
Distribution of minor elements in miscibility gap of
Cu-Fe-As-C system
Three experimental sets were investigated at 1473 K. The
first set is concerned with cobalt and nickel, the second one
with silver and platinum, while the last one with sulfur as the
minor elements. The mass% ratio of the total charge,
MFe =MCu , was kept at 1/1, and the content of arsenic was
varied from 0 to 10 mass%, while the weight composition
was 1 mass% for each minor element. The experimental
procedure was identical to that previously described.
3.
Results
3.1 Phase relations in Fe-As-C ternary system
The liquidus line saturated with carbon at 1473 K is shown
in Fig. 1. It represents an almost straight line against the iron
content, and the solubility of carbon in the melt sharply
decreases with increasing arsenic content. The obtained
liquidus composition saturated with carbon in the Fe-C
binary system agrees well with the reported value.7) The
solubility of carbon7) and arsenic6) in the liquid iron and solid
-iron phases was also plotted in Fig. 1. The estimated
liquidus and solidus lines in the iron-rich corner of the Fe-AsC system are also illustrated in Fig. 1, with dashed lines
which simply connect between the compositions in each
binary system.
3.2
Phase relations in miscibility gap of Cu-Fe-As-C
system
The Cu-Fe-As system saturated with carbon at 1473 K
presents a large miscibility gap where iron-rich and copperrich phases coexist. The compositions of these phases are
listed in Table 1, while the phase relations for the mass%
ratios of the charge, MCu =MFe , with 1/3, 1/1 and 3/1 are
illustrated in Figs. 2, 3 and 4, respectively, in relation to the
mole fractions of carbon (NC ) and arsenic (NAs ) in both
Phase equilibrium compositions of Cu-rich and Fe-rich phases in the Fe-Cu-As system saturated with carbon at 1473 K.
mass% in the charge
Cu/Fe
2.3
mass% in Cu-rich phase
mass% in Fe-rich phase
Fe
Cu
As
3.16
96.8
0
0.03
91.0
5.01
0
3.98
3.93
91.8
4.24
0.03
89.6
4.93
1.75
3.74
4.41
5.04
88.9
86.0
6.62
8.94
0.04
0.04
87.6
85.3
5.42
5.72
3.38
5.69
3.57
3.32
6.75
82.0
11.2
0.03
82.3
6.76
7.89
3.08
9.72
77.6
12.6
0.03
80.9
5.74
10.6
3.15
96.8
0
0.03
91.0
5.01
0
3.98
4.15
92.5
3.36
0.03
89.9
5.00
1.33
3.79
4.99
5.59
89.2
86.3
5.74
8.12
0.04
0.04
88.3
86.0
5.12
5.92
2.93
4.69
3.63
3.39
7.29
82.6
10.1
0.03
84.0
6.00
6.87
3.17
9.18
78.7
12.1
0.04
80.4
7.30
9.35
2.93
3.17
96.8
0
0.03
91.0
4.99
0
3.99
4.00
93.4
2.56
0.03
90.1
4.96
1.09
3.82
4.49
5.15
90.4
87.8
5.07
7.03
0.03
0.04
88.5
86.5
5.48
5.80
2.31
4.20
3.69
3.49
6.10
84.8
9.07
0.04
83.9
6.90
5.83
3.32
8.50
79.7
0.04
81.9
6.72
8.34
3.02
11.8
C
Fe
Cu
As
C
2.80
Phase Relations and Distribution of Some Minor Elements in Cu-Fe-As System Saturated with Carbon at 1473 K
copper-rich
phase
N As
0.12
1473K
mass% Cu / mass%Fe
= 1/3
0.08
iron-rich
phase
0.04
0
0
0.04
0.08
0.12
0.16
NC
Fig. 2 Relation between NAs and NC in Cu-rich and Fe-rich phases in the
Cu-Fe-As system saturated with carbon at 1473 K: mass%Cu/
mass%Fe = 1/3 in the charge.
copper-rich
phase
N As
0.12
1473K
mass% Cu / mass%Fe
= 1/1
0.08
iron-rich
phase
0.04
0
0
0.04
0.08
0.12
0.16
NC
Fig. 3 Relation between NAs and NC in Cu-rich and Fe-rich phases in the
Cu-Fe-As system saturated with carbon at 1473 K: mass%Cu/
mass%Fe = 1/1 in the charge.
copper-rich
phase
phases. When arsenic is added to the Cu-Fe system saturated
with carbon, it is preferentially enriched in the copper-rich
phase with a considerably small amount of iron and a
negligibly small amount of carbon, while carbon and iron
form the iron-rich phase with a smaller amount of arsenic
when compared with that in the copper-rich phase. With
increasing arsenic amount in the charge, the content of
carbon in the iron-rich phase decreases, while that in the
copper-rich phase is almost constant at about 0.03 mass%.
Furthermore, as listed in Table 1, the copper content in the
copper-rich phase decreases with increasing arsenic content,
while the iron content increases. On the contrary, the copper
content in the iron-rich phase increases with increasing
arsenic content while the iron content decreases.
It is noted in Figs. 2, 3 and 4 that the tie lines connecting
the compositions in both phases do not cross with each other
and the end points of these tie lines are almost located on
smooth lines which correspond to the miscibility gap lines.
Furthermore, the miscibility gap lines in Figs. 2, 3 and 4 are
almost identical with each other. These may suggest that the
miscibility gaps for the systems with MCu =MFe ¼ 1=3, 1/1
and 3/1 are located on a common plane in a tetrahedral
diagram representing the iron, copper, carbon and arsenic
compositions.
Since the solubility of carbon in the copper-rich phase is
very small, the composition diagram for the quaternary
system may be simplified to a pseudo-ternary diagram in
which iron and carbon are regarded as one constituent. The
phase relations in the Cu-(Fe-C)-As pseudo ternary system
saturated with carbon at 1473 K are shown in Fig. 5, together
with those in the Cu-Fe-As ternary system at 1423 K which
were determined by one of the authors.4) The immiscible
region composed of the liquid iron-rich phase, L1 , and the
liquid copper-rich phase, L2 , is clearly reproduced in Fig. 5. It
is found that the end points of the tie lines in the copper-rich
region for three systems with MCu =MFe ¼ 1=3, 1/1 and 3/1
are almost located on a line which corresponds to the
immiscibility gap line. Furthermore, it is noted that this
miscibility gap line is very close to the liquidus line
equilibrating with the solid -iron in the Cu-Fe-As ternary
system.
3.3
1473K
mass% Cu / mass%Fe
= 3/1
Distribution of minor elements in miscibility gap of
Cu-Fe-As-C system
The distribution ratio of a minor element X between the
0.08
As
iron-rich
phase
0.6
+C
(Fe
N
Present work
Cu-Fe-As at 1423 K
0.8
N As
0.04
0.4
Cu / Fe (in weight)
1/3
1/1
3/1
)
N As
0.12
2853
Mendoza
0.2
0
0
0.04
0.08
0.12
0.16
NC
Fig. 4 Relation between NAs and NC in Cu-rich and Fe-rich phases in the
Cu-Fe-As system saturated with carbon at 1473 K: mass%Cu/
mass%Fe = 3/1 in the charge.
(Fe+C)
0.2
0.4
0.6
N Cu
0.8
Cu
Fig. 5 Phase relations in the Cu-(Fe-C)-As pseudo ternary system saturated with carbon at 1473 K.
2854
L. Voisin, H. M. Henao and K. Itagaki
phase relations in this system as well as the treatment of
arsenic in the by-products. On the basis of the present data for
the miscibility gap and the activity data for the Cu-Fe-As
system reported by Hino and Azakami,8) Raoultian activity
coefficients of arsenic in the copper-rich and iron-rich phases
in the miscibility gap of Cu-Fe-As system saturated with
carbon at 1473 K were derived as follows.
Equation (2) is established in the equilibrium condition.
100
10
Co
Ni
LXFe/Cu
S
1
Pt
½ax ¼ ½x ½Nx ¼ hx ihNx i ¼ hax i
0.1
Ag
0.001
0
2
4
6
8
10
12
mass% As in charge
Fig. 6 Distribution ratios of minor elements in relation to the arsenic
content in the charge in the Cu-Fe-As system saturated with carbon at
1473 K.
liquid iron-rich and copper-rich phases in the Cu-Fe-As
system saturated with carbon, LX Fe/Cu , is defined as follows.
LX Fe/Cu ¼ ½mass% XFe =hmass% XiCu
ð1Þ
Where [ ]Fe indicate the iron-rich phase and h iCu the copperrich phase. By the definition, the element X will be
concentrated in the copper-rich phase when the value of
distribution ratio is less than unity. Hence, the smaller value
is preferable when a process for treating the by-products
containing arsenic is considered, in which the valuable
elements including copper will be recovered into the copperrich phase, while the less valuable iron eliminated into the
iron-rich phase.
The distribution ratios of silver, platinum, cobalt, nickel
and sulfur are shown in Fig. 6, in relation to the arsenic
content in the charge. The distribution ratio of silver tends to
increase and those of cobalt and nickel decrease with
increasing arsenic content, while those of sulfur and platinum
change very slightly. It is noted that the distribution ratio at a
given arsenic content decreases in the order of cobalt, nickel,
sulfur, platinum and silver. LAg Fe/Cu presents very small
values of less than 0.01 in the whole range of arsenic
composition, while LCo Fe/Cu in the range of lower arsenic
composition considerably large values of more than 10.
LNi Fe/Cu is also larger than unity in the whole range of arsenic
composition. LS Fe/Cu is slightly larger than unity, while
LPt Fe/Cu slightly less than unity. These results have a very
important implication when the treatment of by-products
containing arsenic is considered, as will be discussed later.
4.
4.1
Discussion
Activity coefficient of arsenic in miscibility gap of
Cu-Fe-As-C system
The thermodynamic properties of arsenic in the Cu-Fe-As
system saturated with carbon are of major concern for the
Where x is Raoultian activity coefficient of arsenic, Nx is
mole fraction of arsenic, and [ ] and h i denote the iron-rich
and copper-rich phases, respectively.
The content of carbon in the copper-rich phase was barely
different from that indicated in the Cu-Fe system saturated
with carbon.3) Since this value is very small at about
0.03 mass%, this phase may be treated as the Cu-Fe-As
ternary system. Hence, hAs i in eq. (2) is known by
combining the reported activity data in the ternary system8)
with the present data for the miscibility gap line in the
copper-rich region. Then, As in the iron-rich phase can be
derived from eq. (2), in relation to the arsenic content.
The activity coefficients of arsenic (the standard state of
arsenic activity is pure liquid arsenic) in the iron-rich and
copper-rich phases in the miscibility gap of Cu-Fe-As system
saturated with carbon for the mass% ratios of the charge with
MCu =MFe ¼ 1=3, 1/1 and 3/1 at 1473 K are shown in Fig. 7,
in relation to the arsenic content in both phases. It is noted
that the activity coefficients in both phases represent
considerably small values with less than 0.03. It is also
found that, at a given arsenic content, the activity coefficient
in the iron-rich phase is about 2 times larger than that in the
copper-rich phase. On the contrary, according to the activity
data for the Fe-As and Cu-As binary systems reported by
Hino and Azakami,8,9) the activity coefficient of arsenic in the
Fe-As system is smaller than that in the Cu-As system. This
discrepancy may be ascribed to the effect of carbon which is
0.03
1473K
iron-rich phase
%Cu / %Fe
1/3
1/1
3/1
0.02
γ*As
0.01
ð2Þ
0.01
copper-rich phase
0
0
0.025
0.050
0.075
0.100
0.125
N As
Fig. 7 Activity coefficient of arsenic at the boundaries in the miscibility
gap of the Cu-Fe-As system saturated with carbon at 1473 K (standard
state: pure liquid As).
Phase Relations and Distribution of Some Minor Elements in Cu-Fe-As System Saturated with Carbon at 1473 K
contained in the iron-rich phase with the amount of
34 mass%. It is considered that the interaction between
arsenic and iron may be weakened due to a strong chemical
affinity of carbon to iron.
4.2
Thermodynamic analysis for distribution ratio of
minor elements
The experimental results for the distribution ratio of minor
elements (X) between the iron-rich and copper-rich phases in
the miscibility gap of Cu-Fe-As system saturated with carbon
will be thermodynamically discussed on the basis of eq. (2)
with X as minor elements. By the conversion of mole fraction
to mass%, the distribution ratio of X between both phases, as
given in eq. (1), can be thermodynamically expressed by the
following equation.
LX Fe/Cu ¼ ½nT hX i=hnT i½X ð3Þ
Where ½nT and hnT i denote the total number of moles of
100 g iron-rich and copper-rich phases, respectively.
The ratio of activity coefficients, hX i=½X , can be derived
from eq. (3) by using the present data for the distribution
ratio, shown in Fig. 6, and for the compositions of iron-rich
and copper-rich phases, listed in Table 1. The calculated
results for cobalt, nickel, sulfur, platinum and silver are
shown in Fig. 8, in relation to the arsenic content in the
charge. The ratio of activity coefficients at a given arsenic
content decreases in the order of cobalt, nickel, sulfur,
platinum and silver.
Since the data on the activity coefficients of these minor
elements in the Cu-Fe-As system saturated with carbon are
lacking, the tendency observed in Fig. 8 will be discussed on
the basis of available data for the activity coefficients of these
elements in the Cu-X and Fe-X binary alloys without carbon.
The Raoultian limiting activity coefficients, o X , for Ag, Pt,
Ni and Co in the Cu-X systems10–13) and o X for Pt, Ni and Co
in the Fe-X systems14–16) at 1473 K were evaluated from the
published data by using the regular solution model. o Ag in
100
10
Co
<γ >Cu /[γ]Fe
Ni
S
1
Pt
0.1
0.01
Ag
0.001
0
2
4
6
8
10
12
mass% As in charge
Fig. 8 Ratios of activity coefficient of minor elements in relation to the
arsenic content in the charge in the Cu-Fe-As system saturated with carbon
at 1473 K.
2855
the Fe-Ag system was estimated from the phase diagram.17)
On the other hand, the literature values for the Henrian
activity coefficient of sulfur at 1 mass% sulfur, fS , were used
for the Cu-S system18) and the Fe-S19) system. The calculated
ratios of hX i=½X or h fS i=½ fS are 12, 4, 0.8, 2 and 0.03 for
cobalt, nickel, sulfur, platinum and silver, respectively. The
values for Co, Ni, S and Ag are in fairly good agreement with
those indicated at 0 mass% As in Fig. 8. The very small ratio
for silver is ascribed to the very large activity coefficient in
the iron phase, while the considerably large one for cobalt to
the considerably large activity coefficient in the copper
phase. This may suggest that the chemical affinity of silver
for copper is much stronger than that for iron, while the
chemical affinity of cobalt for iron is stronger than that for
copper. More detailed discussions would be made possible if
the data for the activity coefficients of these minor elements
in the Cu-Fe system saturated with carbon were available,
especially for Pt.
It is noted in Fig. 8 that the ratio of activity coefficient for
silver increases with increasing arsenic content in the charge
while those for cobalt and nickel decrease. These behaviours
can be basically explained by considering the abovementioned chemical affinity of these elements as well as
the change in the contents of iron and copper in the copperrich and iron-rich phases when the arsenic content in the
charge is increased. As listed in Table 1, the mutual solubility
of iron in the copper-rich phase and of copper in the iron-rich
phase increase with increasing arsenic content in the charge.
When combined with the chemical affinity of silver to copper
and iron, it is suggested that, with increasing arsenic content
in the charge, the activity coefficient of silver in the copperrich phase increases while that in the iron-rich phase
decreases. This may results in the increasing activity
coefficient ratio, as shown in Fig. 8.
4.3 Mass balances in the proposed process
Based on the present experimental results, the material
balances were evaluated for the new process proposed by the
authors. In the process, excess carbon is added to the Cu-Fe
base speiss to make immiscible copper-rich and iron-rich
phases at a fairly low temperature of about 1500 K and to
recover valuable copper and some other metals in the copperrich phase and eliminate less valuable iron into the iron-rich
phase. It might be disposed in a less stringent condition if
stable in the atmosphere.
It is supposed in the calculation that 1000 kg of speiss
containing iron, copper and arsenic with 45, 45 and
9.5 mass%, respectively, and silver, platinum, sulfur, nickel
and cobalt with each 0.1 mass% is treated at 1473 K by
adding the minimum amount of carbon with 15.1 kg that is
required for its saturation in the melts. Since the summation
of equilibrium partial pressures of predominant As and As2
gas species over the corresponding Cu-Fe-As alloy at 1473 K
is very small at about 1.5 Pa, the loss of arsenic by
volatilization was neglected in the calculation. The calculated results are listed in Table 2, representing the weight
amounts (kg) of all the elements in each phase and their
fractional distribution (%) between both phases.
It is indicated in Table 2 that more than 90% of iron and
more than 98% of carbon in the charge will be distributed
2856
L. Voisin, H. M. Henao and K. Itagaki
Table 2
Mass balance in the treatment of 1000 kg of Cu-Fe-As speiss under saturation of carbon at 1473 K.
In the charge
Element
mass%
Weight amount (kg)
weight amount (kg)
Cu
45.0
450
Fe
45.0
450
Cu-rich phase
415
44.0
Cu-rich phase
34.7
92.3
406
95.0
—
15.1
Ag
0.100
1.00
0.992
0.008
99.2
Pt
0.100
1.00
0.537
0.463
53.7
46.3
S
Ni
0.100
0.100
1.00
1.00
0.497
0.462
0.503
0.538
49.7
46.2
50.3
53.8
0.782
21.8
78.2
51
49
0.100
100
1.00
1015
0.218
514
into the iron-rich phase, while more than 92% of copper into
the copper-rich phase. The fractional distribution of arsenic
in the copper-rich phase is fairly larger than that in the ironrich phase. It is noted that the fractional distribution of silver
in the copper-rich phase is extremely large at more than 99%
and that of cobalt in the iron-rich phase is also considerably
large at 78.2%. These results suggest that, when the recovery
of valuable elements and the elimination of iron from the CuFe base speiss are considered by means of the phase
separation, the recovery of valuable silver and copper into
the copper-rich phase as well as the elimination of less
valuable iron into the iron-rich phase might be feasible even
though the proportions of valuable cobalt and nickel lost in
the iron-rich phase are considerably large. The copper-rich
alloy may be further treated in a pyrometallurgical or
hydrometallurgical process to extract silver and copper,
while the less valuable iron-rich alloy may be deposited if the
contents of cobalt and nickel in the initial charge are small.
Summary
As a fundamental study for treating the speiss, which is a
by-product with a considerably high content of arsenic in
nonferrous smelting processes, the phase relations in the
miscibility gap of Cu-Fe-As system saturated with carbon
and the distribution of some minor elements between the
phases in the miscibility gap were investigated at 1473 K.
The results are summarized as follows.
(1) A miscibility gap composed of copper-rich and ironrich phases extends over the wide concentration range.
Arsenic distributes in both phases, while carbon
preferentially in the iron-rich phase.
(2) Raoultian activity coefficients of arsenic in the iron-rich
phase are considerably small at about 0.03 even though
they are about 2 times larger than those in the copperrich phase.
(3) For minor elements, the distribution ratios LX Fe/Cu , at a
given arsenic content in the charge decrease in the order
of cobalt, nickel, sulfur, platinum and silver. The
LAg Fe/Cu in the range of lower arsenic content is very
small at less than 0.03, while that for cobalt is
considerably large at more than 10. These suggest that
most of silver and a large part of cobalt in a by-product
14.9
501
54.4
7.7
90.2
9.50
0.159
43.4
9.78
Fe-rich phase
C
Co
5.
Fe-rich phase
As
total
51.6
Fractional distribution (%)
1.05
45.6
98.9
0.84
will be enriched in the copper-rich and iron-rich phases,
respectively.
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