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Effect of oxygen on the CuCu2SeAg system
Minerals Engineering, Vol. 12, No. 12, pp. 1441-1457, 1999
Pergamon 0892-6875(99)00133-8
© 1999 Published by Elsevier Science Ltd All rights reserved 0892-6875/99/$ - see front matter
EFFECT OF OXYGEN ON THE Cu-Cu2Se-Ag SYSTEM
M. L A M O N T A G N E §, C. A. PICKLES § and J. M. TOGURI ¶ Department of Materials and Metallurgical Engineering, Kingston, Ontario, Canada, K7L 3N6 E-mail: [email protected] ¶ Department of Metallurgy and Materials Science, University of Toronto, Toronto, Ontario, Canada, M5S 3E4 (Received I April 1999; accepted 1 September 1999)
ABSTRACT A large percentage of the world's silver supply is produced as a by-product of the copper industry. The silver is found in the copper anodes which are upgraded by electrorefining. The anode composition and the phase distribution in the anode affect the electroreftning step and subsequently the separation processes for the various elements which are present in the anode. In particular, the distribution of silver and the other precious metals between the copper-rich phase and the copper-selenide rich phase in the anodes has an effect on their recovery. In the present research the effect of oxygen on the Cu-Se-Ag (Pt, Pd, Au, or Ni) system was studied Samples of copper-rich liquid and copper selenide-rich liquid were equilibrated at temperatures in the range of 1130°C to 1223°C. The silver content of both the phases reached a constant value after about two hours. Also, the oxygen content of the copper-rich phase reached an essentially constant value. However, the oxygen content of the copper-selenide rich phase continuously increased due to the production of oxide phases in the melt. The oxygen content of both phases increased with the partial pressure of oxygen. At high oxygen potentials the silver distribution ratio between the copper and the copper selenide phases decreased because of the oxidation of some of the copper selenide to copper oxide. Silver as either oxide or metal has a much higher solubility in copper oxide than copper selenide and thus the silver distribution ratio decreased Nickel additions resulted in a significant increase in the oxygen content of both phases. © 1999 Published by Elsevier Science Ltd. All rights reserved
INTRODUCTION In the conventional processes for copper production, the molten copper from the fire refining step is cast into anodes for electrorefining . The composition and the phase distribution of the anode affect the electrorefining step and the subsequent processes. In particular, the phase distribution in the anode determines the impurity contamination in the refining electrolyte and possibly the refined cathode. Chen and Dutrizac (1987-1991, 1993) and Forsen et al. (1985, 1987) have recently performed studies on the distribution and the mineralogy of the impurities in industrial copper anodes. In these investigations, several different analytical techniques were employed to study the mineralogy of anodes from five copper refineries.
1442
Effect of oxygenon the Cu-Cu2Se-Agsystem
Electron microprobe analysis of the anodes showed the following: In the copper matrix, the silver and nickel were present at high levels, the lead and arsenic were present at low levels, while antimony and bismuth were not detected (Chen and Dutrizac, 1989). The nickel content of the copper matrix can be as high as 0.3 mass percent. The nickel is present in solid solution. At nickel contents of greater than 0.3 mass percent the nickel is present as nickel oxide (NiO), Kupferglimmer (Cu3Niz_xSbO6_x) and Cu-Fe-Ni oxide phases ( Forsen et al., 1985, 1987). About ninety-nine percent of the silver is present as a metastable solid solution in the copper matrix. The rest of the silver is present as particles and/or thin shells of metallic silver surrounding particles such as Cuz(Se, Ye) (Chert and Dutrizac, 1990). About thirty mass percent of the arsenic is present in the copper matrix. Also, a small amount of bismuth and lead are present. In most cases, the bismuth was below the detection limit (Chen and Dutrizac, 1991 ). Secondary Ion Mass Spectrometry and Micro-Proton-Induced X-ray Emission were used to determine the gold content and location (Chen and Dutrizac, 1989). Generally, the gold was found in solid solution in the copper metal matrix. No discrete gold phases were present in the copper anodes. Chen and Dutrizac (1989) determined that cuprous oxide (Cu20) is the most abundant inclusion phase. It is normally present as isolated particles or in association with Cu2(Se, Te), NiO and various C u - P b - A s - S b - B i oxides. Selenium is present as copper selenide (Cu2ae) with some tellurium. The copper selenide inclusions are primarily associated with cuprous oxide or at the copper grain boundaries. Silver, tellurium and sulfur have been found in solid solution in the copper selenide. The sulfur presence is relatively uncommon. The silver content of the inclusions accounts for only about one percent of the total silver content of the anodes. Tellurium is usually found associated with the copper selenide. As stated above, at high nickel contents, that is greater than 0.3 mass percent, inclusions of NiO, Kupferglimmer and Cu-Fe-Ni oxide phases are formed (Forsen et al., 1985). Other complex oxides, which are found in the anodes include: Cu-Pb oxides, Cu-Pb-Bi oxides, Cu-Pb-As oxides, C u - P b - S b oxides, C u - P b - A s - S b oxides, and C u - P b - A s - S b - B i oxides, and Cu-Bi-As oxides (Chen and Dutrizac, 1989, 1991). As discussed above, the majority of the silver in the anode is found in the copper matrix. The remainder is usually found to be associated with the copper selenide and therefore the C u - S e - A g system is of interest. In the present work, in order to examine the distribution of silver and the other additions, the overall composition of about 13 mass percent Se was chosen. At this composition, at temperatures over 1100°C, there is a miscibility gap and two liquid phases are formed, a copper-rich liquid and a Cu2Se-rich liquid. In the present research, the effect of oxygen on this system is discussed. Firstly, the information available in the literature on the relevant copper-selenium and the oxygen-containing systems is reviewed. Secondly, an experimental technique is described in which the two liquid phases, that is copper and copper selenide, were equilibrated under controlled atmospheres. Various additions such as Ag, Ni, Au, Pt, and Pd were made to the system. The effects of oxygen on the two phases and the silver distribution are discussed.
The copper-selenium (Cu-Se) system The phase diagram for the Cu-Se 1987). The diagram indicates that contains two large miscibility gaps percent copper) above 1100°C and above 540°C.
system, as shown in Figure 1, has generally been accepted (Moffat, three compounds exist: Cu2Se, Cu3Se2, and CuSe. This system also in the ranges of about 2 to 36 mass percent selenium (98 to 64 mass about 58 to 98 mass percent selenium (42 to 2 mass percent copper)
M. Lamontagne et al
1443
WEIGHT % 5e 20 3 0 4-0 5O 6O 70 I
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(ot-Cu=Se)
,.,
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to
20
230 4-0 50 60 ATOM % Se
70
80
90
Se
Fig. 1 The Cu-Se phase diagram (Moffat, 1987). Babitsyna et aL (1975) studied the Cu-Se system from 0 to 80 atom% Se at temperatures of greater than 1100°C. It was determined that the miscibility gap of a Cu-rich liquid and a Cu2Se-rich liquid began at 1100°C and the phase field ended when the selenium content reached 30 atom%. The transformation of 13CuzSe to cx-Cu2Se occurred at 162°C. On the other hand, Heyding (1966) found that the transformation occurred at 131 °C. Burylev et aL (1974) performed studies at 0 to 40 atom% Se in the temperature range of 1000°C to 1500°C. They concluded that the miscibility gap ranged from 1.5 atom% Se to 30.7 atom% Se at 1107°C. Included in the work of Burylev et aL (1974) is an equation for the temperature dependence of the selenium solubility in copper which is as follows: log Xse -
1790
0.555
T where Xse is the atom fraction of dissolved selenium.
(1)
1444
Effect of oxygenon the Cu--Cu2Se-Agsystem
In the present research, the miscibility gap of copper-rich liquid containing about 1.5 atom% Se and a copper-selenium liquid with a composition close to that of Cu2Se was of interest. The compound Cu2Se has a congruent melting temperature of 1130°C. However, for a Cu-Se alloy containing about 13 mass percent selenium, the Cu-rich phase and the CuzSe-rich phase are both liquid at 1100°C. Upon cooling and solidification of this liquid alloy and under equilibrium conditions, the solid would consist of almost pure copper and the compound Cu2Se. However, if the liquid alloy was rapidly cooled, i.e. quenched, then the copper-rich phase should contain about 1.5 atom% Se and the Cu2Se-rich phase should contain about 31 atom% Se. The selenium content of the Cu2Se-rich phase would be 3 or 4 atom% lower than that of the compound Cu2Se. Also, it can be seen in Figure 1 that the selenium content of the Cu-rich phase slightly increases with temperature while the selenium content of the CuzSe-rich phase slightly decreases with temperature.
Oxygen in copper anodes The cast copper anodes, which are used in the electrorefining process, always contain some oxygen. Schleon (1987) surveyed thirty-six refineries and found that the total oxygen content ranged from about 130 to 4000 ppm with an average of 1690 ppm. Also, Chen and Dutrizac (1990) in their work, found discrete inclusions of Cu20, Cu-Pb-oxide, Cu-Pb-As-oxide, Cu-Bi-As-oxide, NiO and Cu-Se-O. The presence of these oxides depends both upon the impurity content of the anodes and the oxygen content. Some anodes may contain only one or two of the above compounds while others may contain many more. Therefore, the effect of oxygen on the relevant systems is of considerable interest. As discussed by Chen and Dutrizac (1990), Cu20 is the most prevalent oxide in nearly all copper anodes. The majority of the total oxygen is concentrated at the free surface of the cast anodes. The Cu20 particles are present as either free spheroids or as inclusions associated with Cu2Se, NiO and various complex oxides. If the oxygen content is high enough then a eutectic of Cu-Cu20 may be found between some copper grains. The NiO is formed when the nickel content is greater than 0.3 mass percent, otherwise the nickel is present only in a solid solution in the copper matrix.
Oxygen effects in the Cu-(Ag, Se, Ni, Au, Pt, Pd) system For the A g - C u system, Subramanian and Perepezko (1993) state that the dissolved oxygen content reaches a maximum value of 1 atom% when Cu20 is equilibrated with liquid Ag-Cu alloys at 1027°C. Choudary and Chang (1976) reported that the solubility of oxygen in liquid copper is very small and reaches a maximum of 0.058 at% (0.015 mass percent) at a temperature of 1200°C. In their compendium on the Cu-O system, Hallstedt et aL (1994) show a phase diagram for the Cu-O system at oxygen mole fractions of less than 0.1 at 1130°C to 1227°C. Between 1127°C and 1227°C, the maximum oxygen solubility of a liquid in equilibrium with pure solid copper occurs at a mole fraction of 0.0175. At higher oxygen contents the liquid copper is in equilibrium with copper oxide (Cu20). Between 1127°C and 1227°C the oxygen content of the liquid varies betweeen 0.03 and 0.093, respectively. Cu20 will form upon solidification as the melt undergoes the eutectic reaction at about 1067°C. For oxygen mole fractions above 0.0175, Cu20 will precipitate out above 1067°C and a copper-rich liquid will be in equilibrium with CuzO. Also they showed that if the oxygen potential was below 10 -6.5 a t m then no CuzO should form at temperatures above 968°C. The literature contains some thermodynamic information on the C u - O - i system, where i represents Se, Ag, Ni, Au, Pt, or Pd, but in most cases it is inconsistent. For the Cu-O-Se system, at oxygen levels of the Se order of Xo=10 -4, the interaction coefficient ( ~ ' 0 ) values are -14.1 at ll00°C and -11.5 at 1200°C (Seetharaman and Staffansson, 1988). When the oxygen level was lowered to Xo=10 -6, the interaction coefficient was 8.8 at 1200°C. A similar change in the sign of the interaction coefficient was also found in the C u - O - T e system (Seetharaman, 1992). The authors suggested that the negative interaction coefficient obtained at Xo=10 -4 could be in error as a result of the volatilization of SeO2. This would result in the removal of only a small amount of selenium but a significant amount of oxygen. They suggested that further studies should be made to resolve this effect.
M. Lamontagneet al
1445
For the case of the Cu-O-Ag system, the interaction coefficient ( 6"~'g ) has been reported as 4.52 at 1135°C by Nanda and Geiger (1970), -0.7 by Sigworth and Elliott (1974) from compiled data, - 1.26 by Chiang and Chang (1976), and -1.09 by Turkdogan at 1200°C (1980). The latter three values seem to corroborate one another and the first highly positive value, should likely be disregarded. For the Cu-O-Ni system at 1200°C, the interaction coefficient (,~Ni) was reported to be -7.44 by Sigworth and Elliott (1974) from compiled data, -8.73 by Chiang and Chang (1976), and -8.42 by Turkdogan (1980). All of these values are within experimental error. For the Cu-O-Au system at 1200°C, the interaction coefficient (,~Au) was determined to be 8.6 by Sigworth and Elliott (1974) from compiled data and -1.47 by Turkdogan (1980). Azuma and Ogawa (1975) found the interaction coefficient to be 27 at 1150°C. At 1200°C, Young (1965) determined a value of 3.8 while EI-Naggar and Parlee (1971) report 20.6. Tankins (1970) gives two values at 1550°C, 5.8 and 7.9. Due to the wide disparity between the results of the various studies, an exact value for G0Au is not available. However, it is likely that the value is positive and in the range of 3 to 20 for temperatures between 1150°C and 1550°C. In the Cu-O-Pt system at 1200°C, the interaction coefficient (80at ) was reported to be 38.0 by Sigworth and Elliott (1974) from compiled data and 3.58 by Turkdogan (1980). At 1200°C the values were found to be 19.1 by E1-Naggar and Parlee (1971) and 8.2 by Young (1965). At 1550°C Tankins (1970) reports a value of 4.1. Again, there is a large variation in the experimental results. However, the interaction coefficient is positive and its numerical value is in the range of 3 to 40. The information reported above for the interaction coefficients is relevant to solutions containing copper as the solvent with dilute concentrations of Ag, Ni, Au, Pt and oxygen. However, it should be noted that in the experiments employed to derive the interaction coefficients, usually no information is provided regarding the final oxygen content, However, it would be expected that the amount of oxygen in the solution would have an effect on the interaction coefficient. Furthermore, as discussed previously for the Cu-O-Se system, volatile oxides can form which deplete the system of both the impurity and oxygen. This may be occurring in the Cu-O-Pt system where platinum and oxygen may form the volatile oxide, PtO2, (boiling point of PtOz is 750°C (Samsonov, 1973)). No interaction coefficient data could be found for the Cu-O-Pd system but it should be qualitatively similar to that of the Cu-O-Pt system. Based on the information discussed above it would be expected that silver would not have a significant effect on oxygen while nickel would have a significant and negative interaction coefficient. Thus, nickel would increase the oxygen solubility. On the other hand, gold, platinum and palladium additions should result in a decrease in the oxygen solubility.
EXPERIMENTAL R a w materials
Experimental reagent grade copper foil (99.999%) and selenium pellets (99.99) were employed to produce the copper-rich and the copper selenide-rich liquid phases. The additions were in the form of silver foil (99.999%), nickel powder (99.999%), gold wire (99.99%), electrolytic palladium (99.99%) and platinum (99.99%). Selenium has a low boiling point (684°C, at 1 atm) and thus it was prereacted with copper, to form copper selenide (CuSe), in order to minimize the vapor losses during the subsequent equilibrium experiments. The CuSe was produced from stoichiometric amounts of copper and selenium (44.59 wt% Cu and 55.41 wt% Se) which were mixed and placed into a sealed evacuated quartz tube which was allowed to equilibrate at 200°C for 24 hours in a muffle furnace. The composition of the CuSe phase was confirmed by x-ray
1446
Effect of oxygenon the Cu-Cu2Se-Agsystem
diffraction, In the subsequent equilibrium experiments the CuSe reacts with excess copper to form Cu2Se at 400°C, according to the following reaction: CuSe + Cu = Cu2Se
(2)
Sample preparation Appropriate amounts of copper, selenium, silver and the various impurities were measured to one ten thousandth of a gram using a Mettler balance model AE 160 with an accuracy of +0.0002 g. The total mass of a sample was about five grams. All of the elements were added as the pure metal with the exception of the selenium, for the reasons stated above. The samples were weighed into either a 2 ml alumina crucible or a graphite crucible. The crucible containing the mixture was then suspended in the hot zone of the furnace using Kanthal type A wire.
Equipment A high temperature resistance tube furnace was employed to heat the samples. The nickel-chromium heating elements, which were coated with mullite, could achieve sustained temperatures of 1200°C and short term temperatures up to about 1300°C. The furnace controller was a Cal 7000 which was connected to an Omega Model 650 digital thermocouple which used a Type K thermocouple and the accuracy was about +2°C. The runs made to determine the time required to reach equilibrium were made in an alumina crucible in an atmosphere of 10% H2 and 90% N2. All other runs containing multiple samples, usually three, were performed in a graphite crucible in a high purity N2 atmosphere. In a typical experiment, the gas was flushed through the system for at least one-half-an-hour and then the system was closed so as to minimize the selenium losses. Both experimental methods employed a mullite tube which was situated in the furnace and sealed at either end with gas inlets and outlets as shown in Figure 2. The equipment shown in Figure 2(a) had the gas inlet and the water quench facility, in a water cooled jacket at the bottom, and this setup was used for the time to equilibrium studies. Due to the large volume of water required to effectively quench the 5g samples, this setup was only used for one sample per run. A second setup shown in Figure 2(b), was used to run multiple samples simultaneously. The samples obtained from this setup were quickly removed from the furnace and quenched in a two liter container of distilled water at room temperature. The quenched samples were dried and their masses were recorded. Then, they were sectioned using an Isomer low speed diamond saw. These sections were mounted in an epoxy resin and hand polished to a 0.5 ~tm finish.
Electron microprobe analysis Analysis was performed with a Camebax SX50 electron microprobe. The electron microprobe analyses samples nondestructively and quantitative compositional information is obtained with an accuracy in the range of 1-2% of the elemental concentration. Although two distinct and separate Cu-rich and Cu2Se-rich layers were obtained in the present research, the copper-rich phase contained some Cu2Se particles. These likely became entrapped during the quenching process. Therefore, when analyzing the Cu phase with the microprobe, a portion of a Cu2Se particle which could be below the surface of the sample, may be included in the interaction volume and this could alter the measured composition. The Kanaya-Okayama Range expression may be used to approximate the depth dimension of the interaction volume (Goldstein et al., 1992. The equation which represents the electron range, Rko in ~tm is as follows: Rko = (0.0276 A Eo 1"67)/
(Z°89p)
(3)
where A is the atomic weight in g/mole, Eo is the incident beam energy in keV, Z is the atomic number and 9 is the density in g/era a while the incident beam is at right angles to the surface. The Rko value obtained from this formula describes the radius of a circle whose center is located at the point where the incident beam strikes the surface of the specimen. The depths of electron penetration into the Cu and Cu2Se phases are 1.46 ~tm and 1.99 ktm, respectively. The Cu phase contained spheres of Cu2Se ranging in size from a
M. Lamontagneet al
1447
fraction of a micron to hundreds of microns. As a result, there exists a possible analytical problem regarding Cu2Se-rich particles located just below the specimen surface, which could affect the compositional totals obtained by x-ray analysis. Thus, the data for the Cu-rich phase, in which the selenium concentration was greater than about 3 mass% were rejected. On the other hand, the Cu2Se-rich phase was relatively homogeneous. Each experimental point, which is reported, represents the average of about six different analyses.
Gas
K-T-ct~e Thermoc
K-Type, Thermocout
Gas
Outlet T Gas " " "
?oting
?oling ater
ater
Furnace
Furna Sample
Samp.les in
graphite crucible
,oling ater
I" Quenching Pot
(a)
Co)
Fig.2 Experimental apparatus (a) was used to determine the equilibrium time with single samples and (b) the multiple sample setup was used in the distribution studies.
1448
Effect of oxygenon the Cu-Cu2Se-Agsystem RESULTS AND DISCUSSION
Equilibration time of copper and copper-selenide containing silver Experimental runs were conducted in order to determine the time required to achieve equilibrium with respect to the silver distribution between the Cu and the Cu2Se phases. The composition of the mixture was held constant at 86.2 mass% Cu, 13.4 mass% Se and 0.45 mass% Ag. Equilibrium was achieved when the Ag contents in both the Cu-rich and the Cu2Se-rich phases were constant. The temperature employed was 1130°C . At this temperature, which was the lowest employed in the experimental work, the time to equilibration should be lower than at any higher temperatures. The results are shown in Figure 3, where the silver content in both phases is plotted with respect to time. It may be seen that equilibrium was achieved after approximately two hours at 1130°C. As illustrated in the Figure, the silver content is initially high in the copper phase and decreases as the system approaches equilibrium. On the other hand, the silver content in the CurSe phase is initially low and increases. This behaviour can be explained in terms of the melting sequence of the silver, copper and Cu2Se. First, the silver melts at 961 °C, followed by the copper (melting point of 1083.4°C) and finally the Cu2Se (melting point of 1120°C). Since both the Ag and Cu are liquid before the Cu2Se , then the copper initially contains more silver. As time progresses, the silver diffuses from the Cu phase into the Cu2Se phase until equilibrium is achieved. All subsequent tests in the distribution studies were of four hours duration.
0.8
D
• Cu2Se O Cu
0.7 0.6 0.5
i o -_a
o
o
o
°
0.4
0.3 o
0.2
0.1
0.0
0
I
I
I
I
I
I
I
/
I
I
2
4
6
8
l0
12
14
16
18
20
22
Time (hr) Fig.3 Silver content of the Cu-rich and the Cu2Se-rich phases as a function of time at 1130°C. The microprobe analysis showed that after the four hour experimental runs, the Ag content was the same in both the Cu2Se particles found in the Cu phase and in the bulk, CuzSe layer on top of the Cu phase. This is further confirmation that equilibrium was achieved. The distribution of silver between the Cu and the Cu2Se phases can be represented by the ratio of the concentration of silver in the two phases as follows: LcU/cu2se g =
mass%Ag in Cu mass%Ag
in C u 2 S e
(4)
where L cu/cu2se represents the distribution coefficient of silver between the copper phase and the copper Ag selenide phase. Using the values of mass% Ag(cu)= 0.4287 and mass% Ag(CuzSe) = 0.3925, which are the
M. Lamontagneet al
1449
average values from the microprobe data in the time period of four to 24 hours inclusive, the distribution coefficient is seen to be 1.09 at 1130°C. The selenium concentration of the Cu2Se-rich phase is shown as a function of the equilibrium time at 1130°C in Figure 4. The selenium concentration of pure Cu2Se is 38.32 mass percent. Also, according to the equilibrium phase diagram as shown in Figure 1, the selenium concentration of the Cu2Se-rich phase should be about 36 to 37 mass percent in the temperature range of 1130°C to 1223°C. It can be seen in Figure 4 that the selenium concentration significantly decreases after 20 hours. However, at the four hour equilibration time which was employed in the present experiments the selenium concentration was as expected based on the equilibrium phase diagram. 40 39 38 37 ~
36
~
35
~
33
32 31 30
I
I
I
I
I
I
I
I
I
2
4
6
8
10
12
14
16
18
"!
20
Time (hr)
Fig.4 The selenium content of the Cu2Se-rich liquid phase as a function of time at 1130°C. The average selenium concentrations of the equilibrated Cu-rich liquid and the Cu2Se-rich liquid phases at 1130°C, 1177°C, and 1223°C are shown in Figure 5. The compositions of both of the phases were relatively constant in the temperature range of 1130°C to 1223°C. This data for the miscibility gap is in good agreement with the compositional range of the gap as shown in the phase diagram in Figure 1. Thus, the quenching process was effective as the liquid compositions were retained in the solidified sample. O x y g e n effects
Figure 6 shows the oxygen content of the copper and the copper selenide phases for the time to equilibration experiments as shown previously in Figure 3. The temperature was 1130°C and the oxygen potential was 1.3x10 -22 atm. It can be seen that the oxygen content of the Cu-rich liquid reaches the equilibrium value very quickly and remains constant throughout the experiments. On the other hand, the oxygen content o f the Cu2Se-rich liquid increases continuously. This indicates that some copper oxide (Cu20) and perhaps some copper selenate (CuSeO4) are forming. Also, it is clear that the oxygen content of the Cu2Se-rich phase is always higher than that of the Cu-rich phase. This difference becomes more pronounced with increasing time. All subsequent results are for a processing time of four hours.
1450
Effect of oxygen on the Cu-Cu2Se-Agsystem 1250
[
~
1225
Cu-rich liquid 1 Cu2Se-rich liquid
O
©
I
1200 %4
o
1175
i
1150
i
/ © 1125
I100 0
I
I
i
I
I
i
I
5
10
15
20
25
30
35
Concentration
40
of Se(wt%)
Fig.5 Average selenium content of the Cu-rich and the Cu2Se-rich phases at 1130°C, 1177°C and 1223°C.
1.4 • 0
t
Cu-rich liquid C%Se-rieh liquid Y = 1130°C
1.2
'
x
~' 1.0
0.8 M
o
0.6 3 OI 0.4 . r e .....................• ........................................................................................• 0.2
0.0 0
I
I
I
I
I
I
L
I
2
4
6
8
10
12
14
16
18
Time (hr) Fig.6 Oxygen content of the Cu-rich and Cu2Se-rich phases as a function o f time at 1130°C. Figure 7 shows a plot of the oxygen content of the copper and copper selenide phases as a function of the oxygen potential in the system. The least squares fit for the data gives the following relationships:
M. Lamontagneet al
O c u - r i c h liquid = 0.75 + 7.79 xlO -3 log
P02
1451
(mass percent)
(5)
(mass percent)
(6)
O c u 2 S e - rich liquid = 1.42 + 4.2 x 10 -2 log P02
2.00 • ©
1.75
Cu-rich liquid Cu2Se-rich liquid T = 1177°C
©
1.50 ~. 1.25 =Q
©
1.00 0.75
~1 0.50 0,25 0,00 -25
t
I
I
I
-20
-15
-10
-5
log Po~
Fig.7 Effect of oxygen partial pressure (log P02 ) on the oxygen concentration of the Cu-rich and the Cu2Se-rich phases at 1177°C. The oxygen content of the Cu2Se-rich phase increases more dramatically with the partial pressure of oxygen than in the Cu-rich phase. Again this likely indicates that a second phase such as Cu20 is forming at the higher oxygen potentials. The oxygen content of the Cu-rich phase is not a strong function of oxygen potential. The oxygen concentration in the Cu-rich phase was about 0.7 mass percent and this corresponds to an oxygen mole fraction of 0.027. With reference to the data of Hallstedt et al. (1994) this high oxygen content indicates that the Cu-rich melt was likely in equilibrium with Cu20. At very low oxygen potentials of less than 10 -20 atm, the oxygen content of the Cu2Se-rich phase becomes less than that of the Cu-rich phase. These results indicate that the dissolved oxygen content of the Cu2Se-rich phase is less than that of the copper phase but oxide formation readily occurs in Cu2Se and this would result in an increase in the overall measured oxygen content. Figure 8 shows an X-ray diffraction pattern of the CuzSe-rich layer. This sample was processed at 1177°C in an oxygen partial pressure of 0.21 atmospheres. Under these highly oxidizing conditions some copper oxide (Cu20) formed. In addition, some metallic copper was detected as well as copper selenide. The copper oxide forms according to the following reaction: Cu2Se + 3/2 02
=
Cu20 + SeO2(g)
(7)
since the density of Cu2Se (6.74 g/cc) is higher than that of Cu20 (6.0 g/cc) the majority of this oxide was formed at the surface of the melt. The copper selenate could form according to the following reaction: Cu2Se + 202 = Cu2Se04
(8)
1452
Effect of oxygen on the Cu-Cu~Se-Agsystem
Cn
Cu~S.
C.
CuF~¢
Cn
CnSo0~
10
l 30
20
40
~
Cn20
I
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60
70
20 (degree) Fig.8 X-ray diffraction pattern of the Cu2Se phase at 1177°C at Po2 =0.21 atrn. Dutrizac (1990) has reported the presence of Cu20 and Cu-Se-O compounds in copper anodes. However, most of the copper oxide in the industrial anodes likely forms as a result of the oxidation of the bulk copper rather than Cu2Se. Figure 9 shows an electromicrograph of the upper portion of the Cu2Se-rich layer. It can be seen that an eutectic forms between the Cu2Se dendrites. This eutectic is likely a mixture of CuzSe (light) and Cu20 (dark). The lamellea in the eutectic were extremely fine (less than 1gtm) and thus their exact composition could not be determined.
Cu2Se-Cu20 eutectic
::::~>:.:?.;.g:. -' ~!.
.~:,..~,.~' ~~?.~.
"!-
:%:
Cu, Se
• ..%. .... ~
~:
%'::"
"~i
Fig.9 Electromicrograph of the Cu2Se phase containing Cu2Se dendrites with a C u 2 S e - C u 2 0 eutectic between the dendrites. The temperature was 1130°C and Po2 1.8X 10-17 atm. =
M. Lamontagneet al
1453
Effect of additions (Ag, Pt, Pd, Au, and Ni) The effect of the silver content of the two phases on their oxygen content is shown in Figure 10 at temperatures of 1130°C, 1177°C and 1223°C. It is clear that the oxygen concentration in both of the phases is not a strong function of either the silver concentration in the copper or the temperature. This reflects the fact that the interaction between silver and oxygen in both the Cu-rich and the Cu2Se-rich liquids is small for the concentration ranges which were investigated. Similarly, Figure 11 shows that increasing the platinum, palladium, gold and nickel concentrations did not result in any significant change in the oxygen concentrations in the two phases. As expected there was total solubility of the various additions in the Curich phase. However, their solubility in the Cu2Se-rich phase was extremely limited. The impurities in the Cu2Se-rich phase varied in the ranges as follows: 0.0163 to 0.0403% for Ni, 0.0525 to 0.1548% for Au, 0.069 to 0.1353% for Pt, and 0.0163 to 0.044 for Pd. 1.2 • O
1.1 --
Cu-rich liquid Cu2Se-rich liquid
- • A
I.O --
t..
1130°C C u - r i c h liquid CurSe-rich liquid
........... 1177°C
0.9
•
0.8
C u - r i c h liquid C t h S e - r i c h liquid
.....
1223°C
o o~
0.7
o 0.6 0.5
•
/x
/x
0
0.4 0.3 0.0
I
I
~
I
I
I
I
I
I
0.l
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Ag Concentration (mass percent) Fig. 10 Effect of silver concentration of the Cu-rich and Cu2Se-rich phases on the oxygen content of the melts. Figure 12 shows the effect of the various impurities on the average oxygen concentration of the two phases. The oxygen contents of the Cu-rich liquids were similar for the melts containing silver, platinum and gold. The average oxygen content of the palladium-containing melt was almost forty percent lower. This indicates a strong interaction between oxygen and palladium in copper. The oxygen contents of the Cu2Serich liquid were similar for impurity additions of silver, platinum and palladium. However, the average oxygen content of the Cu2Se-rich liquid containing gold was extremely high indicating a strong interaction between oxygen and gold in Cu2Se. In the case of nickel, both the Cu-rich liquid and the Cu2Se-rich liquid had very high oxygen contents. This reflects the high affinity of nickel for oxygen in these melts and possibly the formation of some nickel oxide.
1454
Effect of oxygenon the Ctr-Cu~Se-Agsystem
2.0 1.9 1.8 1.7 1.6 1.5 1.4 gl a
B g
1.3 1.2 1.1 1.0 0.9 0.8
@
0.7 0.6 0.5 0.4
t m~--L--m
0.3 0.2
• O
Pt in Cu-rich liquid Pt in Cu:Se-rich liquid
• /X
Au in Cu-rieh liquid Au in Cu2Se-rich liquid
• []
Pd in Cu-rieh liquid Pd in CuzSe-rich liquid Ni in Cu-rich liquid Ni in CuzSe-rieh liquid
0.1 0.0 0.00
I
I
I
I
I
I
I
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
Impurity element (mass percent)
Fig. 11 Oxygen content of the Cu-rich and the Cu2Se-rich phases as a function of the impurity concentration at 1177°C.
1.50 • O
Cu-rich liquid Cu2Se-rich liquid
0
T = 1177°C 1.25
1.0oe~
w 0.75 -
0.50
0.25
0.00
Ag
I
I
I
t
Pd
Pt
Au
Ni
Impurity
element
Fig. 12 Average oxygen content of the Cu-rich and Cu2Se-rich phases for the various impurities,
M. Lamontagneet al
1455
Figure 13 shows the silver distribution ratio between the Cu-rich and the Cu2Se-rich phases as a function of the silver content of the copper phase at three oxygen pressures. There was not a significant difference between the distribution ratios for oxygen pressures of 0.21 atm and 5xl 0 -6 atm within experimental error. However, at the extremely low oxygen partial pressure of 1.3x10 -22 atm the distribution ratios were consistently higher. As discussed previously, silver should not have a strong interaction with oxygen in either the Cu-rich or the Cu2Se-rich melt. Thus, the low distribution ratios at the higher oxygen potentials likely reflect that some oxidation of the copper selenide phase is occurring and copper oxide can form. It is known that silver oxide could also form under these conditions and silver oxide has a high solubility in copper oxide (Kohlmeyer and Sprenger, 1948). Furthermore, it is reported that copper oxide can dissolve up to ten mass percent metallic silver (Froehlich, 1932). These effects would increase the silver content of the copper selenide phase and thus lower the distribution ratios. 4.0
3.5
•
Po, = 1.3 x 10.22 arm
O
Po=0.21 atm
•
Po~ = 5 x 10"~atm
--
3.0
,. -.•... ...•"
2.5-
2.0
, •..•'
--
..,• ...~•' ...,.'"
1.5
.,•,"
,. ..•.' 1.0
--
0.,.
Y 0.5
©
O
--
0.0 0.0
I
I
I
0.1
0.2
0.3
0.4
I
I
I
0.5
0.6
0.7
0.8
Ag concentration in Cu-rich phase (mass percent)
Fig. 13 Effect of Ag concentration of the Cu-rich phase on the silver distribution ratio at various oxygen partial pressures at 1177°C.
CONCLUSIONS
(1) Samples o f a copper-rich phase and a copper selenide-rich phase containing silver were equilibrated at temperatures of 1130°C to 1223°C at various oxygen potentials. The oxygen content of the copper-rich liquid reached a relatively constant value but the oxygen content of the copper selenide rich phase continuously increased. The silver content in both phases reached an equilibrium value after two hours. (2) The oxidation of the copper selenide-rich phase resulted in the production of some copper oxide and possibly some copper selenate. The copper oxide formed on the surface of the copper selenide. (3) The oxygen content of both phases at four hours of processing varied with the partial pressure of oxygen as follows:
1456
Effectof oxygenon the Cu-Cu2Se-Agsystem
Ocu.richliqui d = 0.75 + 7.79 x10 -3 log P02 Ocu2Se_richliquid = 1.42 + 4.2 x 10-2 log PO2 The silver distribution ratio was lower at higher oxygen potentials due to the preferential oxidation of the Cu2Se-rich liquid. (4) Nickel additions resulted in a significant increase in the oxygen content of both the copper-rich and the copper selenide-rich phases. Gold increased the oxygen content of the copper selenide rich phase while palladium reduced the oxygen content of the copper-rich liquid.
ACKNOWLEDGEMENTS The authors would like to thank the Natural Sciences and Engineering Research Council of Canada (NSERC) for their support of this research. Dr. P. Lindon of Laurentian University of Sudbury, Ontario is acknowledged for providing the facilities for this research.
REFERENCES
Azuma, K., and Ogawa, Y., Effect of Gold, Silver, Tin and Nickel on the Activity of Oxygen in Liquid Copper, Journal of the Mining and Metallurgical Institute of Japan, 1975, 91(2), 77-82. Babitsyna, A.A., Emelyanova, T.A., Cheritsyna, M.A., and Kalinninkov, V.T., The Copper-Selenium System, Russian Journal of Inorganic Chemistry, 1975, 20 (11), 1711-1713. Burylev, B.P., Fedorova, N.N., and Tsemekhman, L. Sh., Equilibrium Diagrams of The Cu-S, Cu-Se and Cu-Te Systems, Russian Journal oflnorganic Chemistry, 1974, 19(8), 1249-1250. Chen, T.T., and Dutrizac, J.E., A Mineralogical Study of the Deportment and Reaction of Silver during Copper Electrorefining, Metallurgical Transactions B, 1989, 20B (June), 345-361. Chen, T.T., and Dutrizac, J.E., Mineralogical Characterization of Anode Slimes -- Part I. Anode Copper from Inco's Copper Cliff Copper Refinery, Canadian Metallurgical Quarterly, 1989, 27(2), 91-96. Chen, T.T., and Dutrizac, J.E., Mineralogical Characterization of Anode Slimes -- Part II. Raw Anode Slimes from Inco's Copper Cliff Copper Refinery, Canadian Metallurgical Quarterly, 1988, 27(2), 97-116. Chen, T.T., and Dutrizac, J.E., Mineralogical Characterization of Anode Slimes -- Part III. Sulphation Reaction Slimes from Inco's Copper Cliff Copper Refinery, Canadian Metallurgical Quarterly, 1988, 27(2), 107-116. Chen, T.T.; and Dutrizac, J.E., Mineralogical Characterization of Anode Slimes -- Part IV. Copper-Nickel-Antimony Oxide (Kupferglimmer) in CCR Anodes and Anode Slimes, Canadian Metallurgical Quarterly, 1989, 28(2), 127-134. Chen, T.T., and Dutrizac, J.E., Mineralogical Characterization of Anode Slimes -- Part V. Nickel Rich Copper Anodes from the CCR Division of Noranda Minerals Inc., Canadian Metallurgical Quarterly, 1990, 29(1), 27-37. Chen, T.T., and Dutrizac, J.E., Mineralogical Characterization of Anode Slimes -- Part VI. Pressure Leached Slimes from the CCR Division of Noranda Minerals Inc., Canadian Metallurgical Quarterly, 1990, 29(4), 293-305. Chen, T.T., and Dutrizac, J.E., Mineralogical Characterization of Anode Slimes -- Part VII. Copper Anodes and Anode Slimes from the Chuquicamata Division of Codelco-Chile, Canadian Metallurgical Quarterly, 1991, 30(2), 95-106. Chen, T.T., and Dutrizac, J.E., Mineralogical Characterization of Anode Slimes -- Part VIII. Silica in Copper Anodes and Anode Slimes, Canadian Metallurgical Quarterly, 1991, 30(3), 173-185. Chen, T.T., and Dutrizac, J.E., Mineralogical Characterization of Anode Slimes -- Part IX. The Reaction of Kidd Creek Anode Slimes with Various Lixiviants, Canadian Metallurgical Quarterly, 1993, 32(4), 267-279.
M. Lamontagneet al
1457
Chen, T.T., and Dutrizac, J.E., Mineralogical Characterization of Anode Slimes from the Kidd Creek Copper Refinery, The Electrorefining and Winning of Copper, Ed. by J. E. Hoffman et al., Warrendale, PA, USA, TMS, 1987, pp. 499-525. Chen, T.T., and Dutrizac, J.E., The Behavior of Silver during the Electrorefining ofCopper, Precious Metals '89, Ed. by M. C. Jha, and S. D. Hill, TMS-AIME, 1989, pp. 377-390. Chen, T.T., and Dutrizac, J.E., The Mineralogy of Copper Electrorefining, Journal of Metals, 1990, 42(8), 39-44. Chiang, T., and Chang, Y.A., The Activity Coefficient of Oxygen in Binary Liquid Metal Alloys, Metallurgical Transactions B, 1976, 7B (Sept.), 453-467. Choudary U.V., and Chang, Y.A., A Thermodynamic Method for Determining the Activities from Ternary Miscibility Gap Data: The Cu-Pb-O System, Metallurgical Transactions B, 1976, 7B (Dec.), 655-660. E1-Naggar, M., and Parlee, N., Oxygen Interaction in Certain Liquid Cu-M-O Systems by a Solid Electrolyte Cell Technique, Metallurgical Transactions, 1971, 2(3), 909-911. Forsen, O., and Lilius, K., Solidification and Electrolysis of Copper Anodes Containing Nickel, Arsenic, Antimony and Bismuth, The Electrorefining and Winning of Copper, Ed. by J. E. Hoffman et al., Warrendale, PA, USA, TMS, 1987, pp. 47-69. Forsen, O., Hettula, E., and Lilius, K., The Behavior of Arsenic, Antimony and Bismuth in the Solidification and Electrolysis of Nickel-Oxygen-bearing Copper Anodes, Physical Chemistry of Extractive Metallurgy, Ed. by V. Kudryk, and Y. K. Rao, TMS-AIME, New York, USA, 1985, pp. 353-377. Froehlich, W., Mitt. Forschungsinst Probieramt Edelmet, 1932, 5, 100-103. Goldstein, J.I., Newbury, D.E., Echlin, P., Joy, D.C., Romig, A.D., Lyman, C.E., Fiori, C., and Lifshin, E., Scanning Electron Microscopy andX-ray Microanalysis, Plenum Press, New York, USA, 1992. Hallstedt, B., Risold, D., and Gaucker, L J., Thermodynamic Assessment of the Copper-Oxygen System, Journal of Phase Equilibria, 1994, 15(5), 483-499 Heyding, R.D., The Copper/Selenium System, Canadian Journal of Chemistry, 1966, 44, 1233-1236. Kohlmeyer, E.J. and Sprenger, K.V., The Oxidation of Silver-Copper Alloys, Z. Anorg. Chemie, 1948, 257, 199-214. Moffat, W.G., Cu-Se, The Handbook of Binary Phase Diagrams, General Electric, 1987, .2, pp. 6-80. Nanda, C.R. and Geiger, G., On the Thermodynamics of Oxygen in Molten Copper, Cu-Se and Cu-Ag Alloys, Metallurgical Transactions, 1970, 1, 1235-1243. Samsonov, G.V., The Oxide Handbook, Plenum Publishing, New York, USA, 1973, pp. 105-115. Schloen, J.H., Electrolytic Copper Refining Tank Room Data, The Electrorefining and Winning of Copper. Ed. by J. E. Hoffman et al., Warrendale, PA, USA, TMS, 1987, pp. 3-18. Seetharaman S., and Staffansson, L. -I., Effect of Selenium on the Activity of Oxygen in Dilute Liquid Copper Alloys, Scandinavian Journal of Metallurgy, 1988, 17, 127-130. Seetharaman, S., Effect of Tellurium on Activity of Oxygen in Dilute Liquid Copper Alloys, Scandinavian Journal of Metallurgy, 1992, 21, 90-92. Sigworth, G.K. and Elliott, J.F., The Thermodynamics of Dilute Liquid Copper Alloys, Canadian Metallurgical Quarterly, 1974, 13(3), 455-461. Subramanian P.R. and Perepezko, J.H., The Ag-Cu (Silver-Copper) System, Journal of Phase Equilibria, 1993, 14(1), 62-75. Tankins, E., Activity Of Oxygen in Cu-Au, Cu-Pt, Cu-Ni, Cu-Co, and Cu-Fe Alloys, Canadian Metallurgical Quarterly, 1970, 9(1), 353-357. Turkdogan, E.T., Physical Chemistry of High Temperature Technology, Academic Press, Toronto, Canada, 1980. Young, D., A Thermodynamic Study of Oxygen in Molten Copper Alloys, Ph.D. Thesis, University of London, 1965.
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© 1999 Published by Elsevier Science Ltd All rights reserved 0892-6875/99/$ - see front matter
EFFECT OF OXYGEN ON THE Cu-Cu2Se-Ag SYSTEM
M. L A M O N T A G N E §, C. A. PICKLES § and J. M. TOGURI ¶ Department of Materials and Metallurgical Engineering, Kingston, Ontario, Canada, K7L 3N6 E-mail: [email protected] ¶ Department of Metallurgy and Materials Science, University of Toronto, Toronto, Ontario, Canada, M5S 3E4 (Received I April 1999; accepted 1 September 1999)
ABSTRACT A large percentage of the world's silver supply is produced as a by-product of the copper industry. The silver is found in the copper anodes which are upgraded by electrorefining. The anode composition and the phase distribution in the anode affect the electroreftning step and subsequently the separation processes for the various elements which are present in the anode. In particular, the distribution of silver and the other precious metals between the copper-rich phase and the copper-selenide rich phase in the anodes has an effect on their recovery. In the present research the effect of oxygen on the Cu-Se-Ag (Pt, Pd, Au, or Ni) system was studied Samples of copper-rich liquid and copper selenide-rich liquid were equilibrated at temperatures in the range of 1130°C to 1223°C. The silver content of both the phases reached a constant value after about two hours. Also, the oxygen content of the copper-rich phase reached an essentially constant value. However, the oxygen content of the copper-selenide rich phase continuously increased due to the production of oxide phases in the melt. The oxygen content of both phases increased with the partial pressure of oxygen. At high oxygen potentials the silver distribution ratio between the copper and the copper selenide phases decreased because of the oxidation of some of the copper selenide to copper oxide. Silver as either oxide or metal has a much higher solubility in copper oxide than copper selenide and thus the silver distribution ratio decreased Nickel additions resulted in a significant increase in the oxygen content of both phases. © 1999 Published by Elsevier Science Ltd. All rights reserved
INTRODUCTION In the conventional processes for copper production, the molten copper from the fire refining step is cast into anodes for electrorefining . The composition and the phase distribution of the anode affect the electrorefining step and the subsequent processes. In particular, the phase distribution in the anode determines the impurity contamination in the refining electrolyte and possibly the refined cathode. Chen and Dutrizac (1987-1991, 1993) and Forsen et al. (1985, 1987) have recently performed studies on the distribution and the mineralogy of the impurities in industrial copper anodes. In these investigations, several different analytical techniques were employed to study the mineralogy of anodes from five copper refineries.
1442
Effect of oxygenon the Cu-Cu2Se-Agsystem
Electron microprobe analysis of the anodes showed the following: In the copper matrix, the silver and nickel were present at high levels, the lead and arsenic were present at low levels, while antimony and bismuth were not detected (Chen and Dutrizac, 1989). The nickel content of the copper matrix can be as high as 0.3 mass percent. The nickel is present in solid solution. At nickel contents of greater than 0.3 mass percent the nickel is present as nickel oxide (NiO), Kupferglimmer (Cu3Niz_xSbO6_x) and Cu-Fe-Ni oxide phases ( Forsen et al., 1985, 1987). About ninety-nine percent of the silver is present as a metastable solid solution in the copper matrix. The rest of the silver is present as particles and/or thin shells of metallic silver surrounding particles such as Cuz(Se, Ye) (Chert and Dutrizac, 1990). About thirty mass percent of the arsenic is present in the copper matrix. Also, a small amount of bismuth and lead are present. In most cases, the bismuth was below the detection limit (Chen and Dutrizac, 1991 ). Secondary Ion Mass Spectrometry and Micro-Proton-Induced X-ray Emission were used to determine the gold content and location (Chen and Dutrizac, 1989). Generally, the gold was found in solid solution in the copper metal matrix. No discrete gold phases were present in the copper anodes. Chen and Dutrizac (1989) determined that cuprous oxide (Cu20) is the most abundant inclusion phase. It is normally present as isolated particles or in association with Cu2(Se, Te), NiO and various C u - P b - A s - S b - B i oxides. Selenium is present as copper selenide (Cu2ae) with some tellurium. The copper selenide inclusions are primarily associated with cuprous oxide or at the copper grain boundaries. Silver, tellurium and sulfur have been found in solid solution in the copper selenide. The sulfur presence is relatively uncommon. The silver content of the inclusions accounts for only about one percent of the total silver content of the anodes. Tellurium is usually found associated with the copper selenide. As stated above, at high nickel contents, that is greater than 0.3 mass percent, inclusions of NiO, Kupferglimmer and Cu-Fe-Ni oxide phases are formed (Forsen et al., 1985). Other complex oxides, which are found in the anodes include: Cu-Pb oxides, Cu-Pb-Bi oxides, Cu-Pb-As oxides, C u - P b - S b oxides, C u - P b - A s - S b oxides, and C u - P b - A s - S b - B i oxides, and Cu-Bi-As oxides (Chen and Dutrizac, 1989, 1991). As discussed above, the majority of the silver in the anode is found in the copper matrix. The remainder is usually found to be associated with the copper selenide and therefore the C u - S e - A g system is of interest. In the present work, in order to examine the distribution of silver and the other additions, the overall composition of about 13 mass percent Se was chosen. At this composition, at temperatures over 1100°C, there is a miscibility gap and two liquid phases are formed, a copper-rich liquid and a Cu2Se-rich liquid. In the present research, the effect of oxygen on this system is discussed. Firstly, the information available in the literature on the relevant copper-selenium and the oxygen-containing systems is reviewed. Secondly, an experimental technique is described in which the two liquid phases, that is copper and copper selenide, were equilibrated under controlled atmospheres. Various additions such as Ag, Ni, Au, Pt, and Pd were made to the system. The effects of oxygen on the two phases and the silver distribution are discussed.
The copper-selenium (Cu-Se) system The phase diagram for the Cu-Se 1987). The diagram indicates that contains two large miscibility gaps percent copper) above 1100°C and above 540°C.
system, as shown in Figure 1, has generally been accepted (Moffat, three compounds exist: Cu2Se, Cu3Se2, and CuSe. This system also in the ranges of about 2 to 36 mass percent selenium (98 to 64 mass about 58 to 98 mass percent selenium (42 to 2 mass percent copper)
M. Lamontagne et al
1443
WEIGHT % 5e 20 3 0 4-0 5O 6O 70 I
I
I
L
=
80
90
I
l
i
e
1400
,
I I
! I
LIQ.,
'
I =
1200
t)
-I-
LIQ. z
Ira I I
I000
t a
•
5e •
ig q)
I
~1
t
3
ta
n
LD
1130 ~
If
t|O0
~'
~-1050
o t |
tJJ D I'IX: Ill a.
800 (r..u) + (,3-Cu,Se)
600
1 \uo.,i !\ ,,
I e I
I I I
-I-
I
LIQ. 3
I I
I I I
.540
,.j I-
(~-CUz.~P_.)
÷
Lie. 3
I t
t I
4-00,
, (
"~ ed t/~ tt~
:~.~ T~J •
200
I
LIQ.. 2
s6z (Cu~
~
v
4o0 t~-¢uSe + ua.3
t
I
~ t'15
2t7 iS-CuSe + ( ~ )
8o
oc-CuSe -t- ( S e )
(ot-Cu=Se)
,.,
Cu
to
20
230 4-0 50 60 ATOM % Se
70
80
90
Se
Fig. 1 The Cu-Se phase diagram (Moffat, 1987). Babitsyna et aL (1975) studied the Cu-Se system from 0 to 80 atom% Se at temperatures of greater than 1100°C. It was determined that the miscibility gap of a Cu-rich liquid and a Cu2Se-rich liquid began at 1100°C and the phase field ended when the selenium content reached 30 atom%. The transformation of 13CuzSe to cx-Cu2Se occurred at 162°C. On the other hand, Heyding (1966) found that the transformation occurred at 131 °C. Burylev et aL (1974) performed studies at 0 to 40 atom% Se in the temperature range of 1000°C to 1500°C. They concluded that the miscibility gap ranged from 1.5 atom% Se to 30.7 atom% Se at 1107°C. Included in the work of Burylev et aL (1974) is an equation for the temperature dependence of the selenium solubility in copper which is as follows: log Xse -
1790
0.555
T where Xse is the atom fraction of dissolved selenium.
(1)
1444
Effect of oxygenon the Cu--Cu2Se-Agsystem
In the present research, the miscibility gap of copper-rich liquid containing about 1.5 atom% Se and a copper-selenium liquid with a composition close to that of Cu2Se was of interest. The compound Cu2Se has a congruent melting temperature of 1130°C. However, for a Cu-Se alloy containing about 13 mass percent selenium, the Cu-rich phase and the CuzSe-rich phase are both liquid at 1100°C. Upon cooling and solidification of this liquid alloy and under equilibrium conditions, the solid would consist of almost pure copper and the compound Cu2Se. However, if the liquid alloy was rapidly cooled, i.e. quenched, then the copper-rich phase should contain about 1.5 atom% Se and the Cu2Se-rich phase should contain about 31 atom% Se. The selenium content of the Cu2Se-rich phase would be 3 or 4 atom% lower than that of the compound Cu2Se. Also, it can be seen in Figure 1 that the selenium content of the Cu-rich phase slightly increases with temperature while the selenium content of the CuzSe-rich phase slightly decreases with temperature.
Oxygen in copper anodes The cast copper anodes, which are used in the electrorefining process, always contain some oxygen. Schleon (1987) surveyed thirty-six refineries and found that the total oxygen content ranged from about 130 to 4000 ppm with an average of 1690 ppm. Also, Chen and Dutrizac (1990) in their work, found discrete inclusions of Cu20, Cu-Pb-oxide, Cu-Pb-As-oxide, Cu-Bi-As-oxide, NiO and Cu-Se-O. The presence of these oxides depends both upon the impurity content of the anodes and the oxygen content. Some anodes may contain only one or two of the above compounds while others may contain many more. Therefore, the effect of oxygen on the relevant systems is of considerable interest. As discussed by Chen and Dutrizac (1990), Cu20 is the most prevalent oxide in nearly all copper anodes. The majority of the total oxygen is concentrated at the free surface of the cast anodes. The Cu20 particles are present as either free spheroids or as inclusions associated with Cu2Se, NiO and various complex oxides. If the oxygen content is high enough then a eutectic of Cu-Cu20 may be found between some copper grains. The NiO is formed when the nickel content is greater than 0.3 mass percent, otherwise the nickel is present only in a solid solution in the copper matrix.
Oxygen effects in the Cu-(Ag, Se, Ni, Au, Pt, Pd) system For the A g - C u system, Subramanian and Perepezko (1993) state that the dissolved oxygen content reaches a maximum value of 1 atom% when Cu20 is equilibrated with liquid Ag-Cu alloys at 1027°C. Choudary and Chang (1976) reported that the solubility of oxygen in liquid copper is very small and reaches a maximum of 0.058 at% (0.015 mass percent) at a temperature of 1200°C. In their compendium on the Cu-O system, Hallstedt et aL (1994) show a phase diagram for the Cu-O system at oxygen mole fractions of less than 0.1 at 1130°C to 1227°C. Between 1127°C and 1227°C, the maximum oxygen solubility of a liquid in equilibrium with pure solid copper occurs at a mole fraction of 0.0175. At higher oxygen contents the liquid copper is in equilibrium with copper oxide (Cu20). Between 1127°C and 1227°C the oxygen content of the liquid varies betweeen 0.03 and 0.093, respectively. Cu20 will form upon solidification as the melt undergoes the eutectic reaction at about 1067°C. For oxygen mole fractions above 0.0175, Cu20 will precipitate out above 1067°C and a copper-rich liquid will be in equilibrium with CuzO. Also they showed that if the oxygen potential was below 10 -6.5 a t m then no CuzO should form at temperatures above 968°C. The literature contains some thermodynamic information on the C u - O - i system, where i represents Se, Ag, Ni, Au, Pt, or Pd, but in most cases it is inconsistent. For the Cu-O-Se system, at oxygen levels of the Se order of Xo=10 -4, the interaction coefficient ( ~ ' 0 ) values are -14.1 at ll00°C and -11.5 at 1200°C (Seetharaman and Staffansson, 1988). When the oxygen level was lowered to Xo=10 -6, the interaction coefficient was 8.8 at 1200°C. A similar change in the sign of the interaction coefficient was also found in the C u - O - T e system (Seetharaman, 1992). The authors suggested that the negative interaction coefficient obtained at Xo=10 -4 could be in error as a result of the volatilization of SeO2. This would result in the removal of only a small amount of selenium but a significant amount of oxygen. They suggested that further studies should be made to resolve this effect.
M. Lamontagneet al
1445
For the case of the Cu-O-Ag system, the interaction coefficient ( 6"~'g ) has been reported as 4.52 at 1135°C by Nanda and Geiger (1970), -0.7 by Sigworth and Elliott (1974) from compiled data, - 1.26 by Chiang and Chang (1976), and -1.09 by Turkdogan at 1200°C (1980). The latter three values seem to corroborate one another and the first highly positive value, should likely be disregarded. For the Cu-O-Ni system at 1200°C, the interaction coefficient (,~Ni) was reported to be -7.44 by Sigworth and Elliott (1974) from compiled data, -8.73 by Chiang and Chang (1976), and -8.42 by Turkdogan (1980). All of these values are within experimental error. For the Cu-O-Au system at 1200°C, the interaction coefficient (,~Au) was determined to be 8.6 by Sigworth and Elliott (1974) from compiled data and -1.47 by Turkdogan (1980). Azuma and Ogawa (1975) found the interaction coefficient to be 27 at 1150°C. At 1200°C, Young (1965) determined a value of 3.8 while EI-Naggar and Parlee (1971) report 20.6. Tankins (1970) gives two values at 1550°C, 5.8 and 7.9. Due to the wide disparity between the results of the various studies, an exact value for G0Au is not available. However, it is likely that the value is positive and in the range of 3 to 20 for temperatures between 1150°C and 1550°C. In the Cu-O-Pt system at 1200°C, the interaction coefficient (80at ) was reported to be 38.0 by Sigworth and Elliott (1974) from compiled data and 3.58 by Turkdogan (1980). At 1200°C the values were found to be 19.1 by E1-Naggar and Parlee (1971) and 8.2 by Young (1965). At 1550°C Tankins (1970) reports a value of 4.1. Again, there is a large variation in the experimental results. However, the interaction coefficient is positive and its numerical value is in the range of 3 to 40. The information reported above for the interaction coefficients is relevant to solutions containing copper as the solvent with dilute concentrations of Ag, Ni, Au, Pt and oxygen. However, it should be noted that in the experiments employed to derive the interaction coefficients, usually no information is provided regarding the final oxygen content, However, it would be expected that the amount of oxygen in the solution would have an effect on the interaction coefficient. Furthermore, as discussed previously for the Cu-O-Se system, volatile oxides can form which deplete the system of both the impurity and oxygen. This may be occurring in the Cu-O-Pt system where platinum and oxygen may form the volatile oxide, PtO2, (boiling point of PtOz is 750°C (Samsonov, 1973)). No interaction coefficient data could be found for the Cu-O-Pd system but it should be qualitatively similar to that of the Cu-O-Pt system. Based on the information discussed above it would be expected that silver would not have a significant effect on oxygen while nickel would have a significant and negative interaction coefficient. Thus, nickel would increase the oxygen solubility. On the other hand, gold, platinum and palladium additions should result in a decrease in the oxygen solubility.
EXPERIMENTAL R a w materials
Experimental reagent grade copper foil (99.999%) and selenium pellets (99.99) were employed to produce the copper-rich and the copper selenide-rich liquid phases. The additions were in the form of silver foil (99.999%), nickel powder (99.999%), gold wire (99.99%), electrolytic palladium (99.99%) and platinum (99.99%). Selenium has a low boiling point (684°C, at 1 atm) and thus it was prereacted with copper, to form copper selenide (CuSe), in order to minimize the vapor losses during the subsequent equilibrium experiments. The CuSe was produced from stoichiometric amounts of copper and selenium (44.59 wt% Cu and 55.41 wt% Se) which were mixed and placed into a sealed evacuated quartz tube which was allowed to equilibrate at 200°C for 24 hours in a muffle furnace. The composition of the CuSe phase was confirmed by x-ray
1446
Effect of oxygenon the Cu-Cu2Se-Agsystem
diffraction, In the subsequent equilibrium experiments the CuSe reacts with excess copper to form Cu2Se at 400°C, according to the following reaction: CuSe + Cu = Cu2Se
(2)
Sample preparation Appropriate amounts of copper, selenium, silver and the various impurities were measured to one ten thousandth of a gram using a Mettler balance model AE 160 with an accuracy of +0.0002 g. The total mass of a sample was about five grams. All of the elements were added as the pure metal with the exception of the selenium, for the reasons stated above. The samples were weighed into either a 2 ml alumina crucible or a graphite crucible. The crucible containing the mixture was then suspended in the hot zone of the furnace using Kanthal type A wire.
Equipment A high temperature resistance tube furnace was employed to heat the samples. The nickel-chromium heating elements, which were coated with mullite, could achieve sustained temperatures of 1200°C and short term temperatures up to about 1300°C. The furnace controller was a Cal 7000 which was connected to an Omega Model 650 digital thermocouple which used a Type K thermocouple and the accuracy was about +2°C. The runs made to determine the time required to reach equilibrium were made in an alumina crucible in an atmosphere of 10% H2 and 90% N2. All other runs containing multiple samples, usually three, were performed in a graphite crucible in a high purity N2 atmosphere. In a typical experiment, the gas was flushed through the system for at least one-half-an-hour and then the system was closed so as to minimize the selenium losses. Both experimental methods employed a mullite tube which was situated in the furnace and sealed at either end with gas inlets and outlets as shown in Figure 2. The equipment shown in Figure 2(a) had the gas inlet and the water quench facility, in a water cooled jacket at the bottom, and this setup was used for the time to equilibrium studies. Due to the large volume of water required to effectively quench the 5g samples, this setup was only used for one sample per run. A second setup shown in Figure 2(b), was used to run multiple samples simultaneously. The samples obtained from this setup were quickly removed from the furnace and quenched in a two liter container of distilled water at room temperature. The quenched samples were dried and their masses were recorded. Then, they were sectioned using an Isomer low speed diamond saw. These sections were mounted in an epoxy resin and hand polished to a 0.5 ~tm finish.
Electron microprobe analysis Analysis was performed with a Camebax SX50 electron microprobe. The electron microprobe analyses samples nondestructively and quantitative compositional information is obtained with an accuracy in the range of 1-2% of the elemental concentration. Although two distinct and separate Cu-rich and Cu2Se-rich layers were obtained in the present research, the copper-rich phase contained some Cu2Se particles. These likely became entrapped during the quenching process. Therefore, when analyzing the Cu phase with the microprobe, a portion of a Cu2Se particle which could be below the surface of the sample, may be included in the interaction volume and this could alter the measured composition. The Kanaya-Okayama Range expression may be used to approximate the depth dimension of the interaction volume (Goldstein et al., 1992. The equation which represents the electron range, Rko in ~tm is as follows: Rko = (0.0276 A Eo 1"67)/
(Z°89p)
(3)
where A is the atomic weight in g/mole, Eo is the incident beam energy in keV, Z is the atomic number and 9 is the density in g/era a while the incident beam is at right angles to the surface. The Rko value obtained from this formula describes the radius of a circle whose center is located at the point where the incident beam strikes the surface of the specimen. The depths of electron penetration into the Cu and Cu2Se phases are 1.46 ~tm and 1.99 ktm, respectively. The Cu phase contained spheres of Cu2Se ranging in size from a
M. Lamontagneet al
1447
fraction of a micron to hundreds of microns. As a result, there exists a possible analytical problem regarding Cu2Se-rich particles located just below the specimen surface, which could affect the compositional totals obtained by x-ray analysis. Thus, the data for the Cu-rich phase, in which the selenium concentration was greater than about 3 mass% were rejected. On the other hand, the Cu2Se-rich phase was relatively homogeneous. Each experimental point, which is reported, represents the average of about six different analyses.
Gas
K-T-ct~e Thermoc
K-Type, Thermocout
Gas
Outlet T Gas " " "
?oting
?oling ater
ater
Furnace
Furna Sample
Samp.les in
graphite crucible
,oling ater
I" Quenching Pot
(a)
Co)
Fig.2 Experimental apparatus (a) was used to determine the equilibrium time with single samples and (b) the multiple sample setup was used in the distribution studies.
1448
Effect of oxygenon the Cu-Cu2Se-Agsystem RESULTS AND DISCUSSION
Equilibration time of copper and copper-selenide containing silver Experimental runs were conducted in order to determine the time required to achieve equilibrium with respect to the silver distribution between the Cu and the Cu2Se phases. The composition of the mixture was held constant at 86.2 mass% Cu, 13.4 mass% Se and 0.45 mass% Ag. Equilibrium was achieved when the Ag contents in both the Cu-rich and the Cu2Se-rich phases were constant. The temperature employed was 1130°C . At this temperature, which was the lowest employed in the experimental work, the time to equilibration should be lower than at any higher temperatures. The results are shown in Figure 3, where the silver content in both phases is plotted with respect to time. It may be seen that equilibrium was achieved after approximately two hours at 1130°C. As illustrated in the Figure, the silver content is initially high in the copper phase and decreases as the system approaches equilibrium. On the other hand, the silver content in the CurSe phase is initially low and increases. This behaviour can be explained in terms of the melting sequence of the silver, copper and Cu2Se. First, the silver melts at 961 °C, followed by the copper (melting point of 1083.4°C) and finally the Cu2Se (melting point of 1120°C). Since both the Ag and Cu are liquid before the Cu2Se , then the copper initially contains more silver. As time progresses, the silver diffuses from the Cu phase into the Cu2Se phase until equilibrium is achieved. All subsequent tests in the distribution studies were of four hours duration.
0.8
D
• Cu2Se O Cu
0.7 0.6 0.5
i o -_a
o
o
o
°
0.4
0.3 o
0.2
0.1
0.0
0
I
I
I
I
I
I
I
/
I
I
2
4
6
8
l0
12
14
16
18
20
22
Time (hr) Fig.3 Silver content of the Cu-rich and the Cu2Se-rich phases as a function of time at 1130°C. The microprobe analysis showed that after the four hour experimental runs, the Ag content was the same in both the Cu2Se particles found in the Cu phase and in the bulk, CuzSe layer on top of the Cu phase. This is further confirmation that equilibrium was achieved. The distribution of silver between the Cu and the Cu2Se phases can be represented by the ratio of the concentration of silver in the two phases as follows: LcU/cu2se g =
mass%Ag in Cu mass%Ag
in C u 2 S e
(4)
where L cu/cu2se represents the distribution coefficient of silver between the copper phase and the copper Ag selenide phase. Using the values of mass% Ag(cu)= 0.4287 and mass% Ag(CuzSe) = 0.3925, which are the
M. Lamontagneet al
1449
average values from the microprobe data in the time period of four to 24 hours inclusive, the distribution coefficient is seen to be 1.09 at 1130°C. The selenium concentration of the Cu2Se-rich phase is shown as a function of the equilibrium time at 1130°C in Figure 4. The selenium concentration of pure Cu2Se is 38.32 mass percent. Also, according to the equilibrium phase diagram as shown in Figure 1, the selenium concentration of the Cu2Se-rich phase should be about 36 to 37 mass percent in the temperature range of 1130°C to 1223°C. It can be seen in Figure 4 that the selenium concentration significantly decreases after 20 hours. However, at the four hour equilibration time which was employed in the present experiments the selenium concentration was as expected based on the equilibrium phase diagram. 40 39 38 37 ~
36
~
35
~
33
32 31 30
I
I
I
I
I
I
I
I
I
2
4
6
8
10
12
14
16
18
"!
20
Time (hr)
Fig.4 The selenium content of the Cu2Se-rich liquid phase as a function of time at 1130°C. The average selenium concentrations of the equilibrated Cu-rich liquid and the Cu2Se-rich liquid phases at 1130°C, 1177°C, and 1223°C are shown in Figure 5. The compositions of both of the phases were relatively constant in the temperature range of 1130°C to 1223°C. This data for the miscibility gap is in good agreement with the compositional range of the gap as shown in the phase diagram in Figure 1. Thus, the quenching process was effective as the liquid compositions were retained in the solidified sample. O x y g e n effects
Figure 6 shows the oxygen content of the copper and the copper selenide phases for the time to equilibration experiments as shown previously in Figure 3. The temperature was 1130°C and the oxygen potential was 1.3x10 -22 atm. It can be seen that the oxygen content of the Cu-rich liquid reaches the equilibrium value very quickly and remains constant throughout the experiments. On the other hand, the oxygen content o f the Cu2Se-rich liquid increases continuously. This indicates that some copper oxide (Cu20) and perhaps some copper selenate (CuSeO4) are forming. Also, it is clear that the oxygen content of the Cu2Se-rich phase is always higher than that of the Cu-rich phase. This difference becomes more pronounced with increasing time. All subsequent results are for a processing time of four hours.
1450
Effect of oxygen on the Cu-Cu2Se-Agsystem 1250
[
~
1225
Cu-rich liquid 1 Cu2Se-rich liquid
O
©
I
1200 %4
o
1175
i
1150
i
/ © 1125
I100 0
I
I
i
I
I
i
I
5
10
15
20
25
30
35
Concentration
40
of Se(wt%)
Fig.5 Average selenium content of the Cu-rich and the Cu2Se-rich phases at 1130°C, 1177°C and 1223°C.
1.4 • 0
t
Cu-rich liquid C%Se-rieh liquid Y = 1130°C
1.2
'
x
~' 1.0
0.8 M
o
0.6 3 OI 0.4 . r e .....................• ........................................................................................• 0.2
0.0 0
I
I
I
I
I
I
L
I
2
4
6
8
10
12
14
16
18
Time (hr) Fig.6 Oxygen content of the Cu-rich and Cu2Se-rich phases as a function o f time at 1130°C. Figure 7 shows a plot of the oxygen content of the copper and copper selenide phases as a function of the oxygen potential in the system. The least squares fit for the data gives the following relationships:
M. Lamontagneet al
O c u - r i c h liquid = 0.75 + 7.79 xlO -3 log
P02
1451
(mass percent)
(5)
(mass percent)
(6)
O c u 2 S e - rich liquid = 1.42 + 4.2 x 10 -2 log P02
2.00 • ©
1.75
Cu-rich liquid Cu2Se-rich liquid T = 1177°C
©
1.50 ~. 1.25 =Q
©
1.00 0.75
~1 0.50 0,25 0,00 -25
t
I
I
I
-20
-15
-10
-5
log Po~
Fig.7 Effect of oxygen partial pressure (log P02 ) on the oxygen concentration of the Cu-rich and the Cu2Se-rich phases at 1177°C. The oxygen content of the Cu2Se-rich phase increases more dramatically with the partial pressure of oxygen than in the Cu-rich phase. Again this likely indicates that a second phase such as Cu20 is forming at the higher oxygen potentials. The oxygen content of the Cu-rich phase is not a strong function of oxygen potential. The oxygen concentration in the Cu-rich phase was about 0.7 mass percent and this corresponds to an oxygen mole fraction of 0.027. With reference to the data of Hallstedt et al. (1994) this high oxygen content indicates that the Cu-rich melt was likely in equilibrium with Cu20. At very low oxygen potentials of less than 10 -20 atm, the oxygen content of the Cu2Se-rich phase becomes less than that of the Cu-rich phase. These results indicate that the dissolved oxygen content of the Cu2Se-rich phase is less than that of the copper phase but oxide formation readily occurs in Cu2Se and this would result in an increase in the overall measured oxygen content. Figure 8 shows an X-ray diffraction pattern of the CuzSe-rich layer. This sample was processed at 1177°C in an oxygen partial pressure of 0.21 atmospheres. Under these highly oxidizing conditions some copper oxide (Cu20) formed. In addition, some metallic copper was detected as well as copper selenide. The copper oxide forms according to the following reaction: Cu2Se + 3/2 02
=
Cu20 + SeO2(g)
(7)
since the density of Cu2Se (6.74 g/cc) is higher than that of Cu20 (6.0 g/cc) the majority of this oxide was formed at the surface of the melt. The copper selenate could form according to the following reaction: Cu2Se + 202 = Cu2Se04
(8)
1452
Effect of oxygen on the Cu-Cu~Se-Agsystem
Cn
Cu~S.
C.
CuF~¢
Cn
CnSo0~
10
l 30
20
40
~
Cn20
I
I
I
50
60
70
20 (degree) Fig.8 X-ray diffraction pattern of the Cu2Se phase at 1177°C at Po2 =0.21 atrn. Dutrizac (1990) has reported the presence of Cu20 and Cu-Se-O compounds in copper anodes. However, most of the copper oxide in the industrial anodes likely forms as a result of the oxidation of the bulk copper rather than Cu2Se. Figure 9 shows an electromicrograph of the upper portion of the Cu2Se-rich layer. It can be seen that an eutectic forms between the Cu2Se dendrites. This eutectic is likely a mixture of CuzSe (light) and Cu20 (dark). The lamellea in the eutectic were extremely fine (less than 1gtm) and thus their exact composition could not be determined.
Cu2Se-Cu20 eutectic
::::~>:.:?.;.g:. -' ~!.
.~:,..~,.~' ~~?.~.
"!-
:%:
Cu, Se
• ..%. .... ~
~:
%'::"
"~i
Fig.9 Electromicrograph of the Cu2Se phase containing Cu2Se dendrites with a C u 2 S e - C u 2 0 eutectic between the dendrites. The temperature was 1130°C and Po2 1.8X 10-17 atm. =
M. Lamontagneet al
1453
Effect of additions (Ag, Pt, Pd, Au, and Ni) The effect of the silver content of the two phases on their oxygen content is shown in Figure 10 at temperatures of 1130°C, 1177°C and 1223°C. It is clear that the oxygen concentration in both of the phases is not a strong function of either the silver concentration in the copper or the temperature. This reflects the fact that the interaction between silver and oxygen in both the Cu-rich and the Cu2Se-rich liquids is small for the concentration ranges which were investigated. Similarly, Figure 11 shows that increasing the platinum, palladium, gold and nickel concentrations did not result in any significant change in the oxygen concentrations in the two phases. As expected there was total solubility of the various additions in the Curich phase. However, their solubility in the Cu2Se-rich phase was extremely limited. The impurities in the Cu2Se-rich phase varied in the ranges as follows: 0.0163 to 0.0403% for Ni, 0.0525 to 0.1548% for Au, 0.069 to 0.1353% for Pt, and 0.0163 to 0.044 for Pd. 1.2 • O
1.1 --
Cu-rich liquid Cu2Se-rich liquid
- • A
I.O --
t..
1130°C C u - r i c h liquid CurSe-rich liquid
........... 1177°C
0.9
•
0.8
C u - r i c h liquid C t h S e - r i c h liquid
.....
1223°C
o o~
0.7
o 0.6 0.5
•
/x
/x
0
0.4 0.3 0.0
I
I
~
I
I
I
I
I
I
0.l
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Ag Concentration (mass percent) Fig. 10 Effect of silver concentration of the Cu-rich and Cu2Se-rich phases on the oxygen content of the melts. Figure 12 shows the effect of the various impurities on the average oxygen concentration of the two phases. The oxygen contents of the Cu-rich liquids were similar for the melts containing silver, platinum and gold. The average oxygen content of the palladium-containing melt was almost forty percent lower. This indicates a strong interaction between oxygen and palladium in copper. The oxygen contents of the Cu2Serich liquid were similar for impurity additions of silver, platinum and palladium. However, the average oxygen content of the Cu2Se-rich liquid containing gold was extremely high indicating a strong interaction between oxygen and gold in Cu2Se. In the case of nickel, both the Cu-rich liquid and the Cu2Se-rich liquid had very high oxygen contents. This reflects the high affinity of nickel for oxygen in these melts and possibly the formation of some nickel oxide.
1454
Effect of oxygenon the Ctr-Cu~Se-Agsystem
2.0 1.9 1.8 1.7 1.6 1.5 1.4 gl a
B g
1.3 1.2 1.1 1.0 0.9 0.8
@
0.7 0.6 0.5 0.4
t m~--L--m
0.3 0.2
• O
Pt in Cu-rich liquid Pt in Cu:Se-rich liquid
• /X
Au in Cu-rieh liquid Au in Cu2Se-rich liquid
• []
Pd in Cu-rieh liquid Pd in CuzSe-rich liquid Ni in Cu-rich liquid Ni in CuzSe-rieh liquid
0.1 0.0 0.00
I
I
I
I
I
I
I
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
Impurity element (mass percent)
Fig. 11 Oxygen content of the Cu-rich and the Cu2Se-rich phases as a function of the impurity concentration at 1177°C.
1.50 • O
Cu-rich liquid Cu2Se-rich liquid
0
T = 1177°C 1.25
1.0oe~
w 0.75 -
0.50
0.25
0.00
Ag
I
I
I
t
Pd
Pt
Au
Ni
Impurity
element
Fig. 12 Average oxygen content of the Cu-rich and Cu2Se-rich phases for the various impurities,
M. Lamontagneet al
1455
Figure 13 shows the silver distribution ratio between the Cu-rich and the Cu2Se-rich phases as a function of the silver content of the copper phase at three oxygen pressures. There was not a significant difference between the distribution ratios for oxygen pressures of 0.21 atm and 5xl 0 -6 atm within experimental error. However, at the extremely low oxygen partial pressure of 1.3x10 -22 atm the distribution ratios were consistently higher. As discussed previously, silver should not have a strong interaction with oxygen in either the Cu-rich or the Cu2Se-rich melt. Thus, the low distribution ratios at the higher oxygen potentials likely reflect that some oxidation of the copper selenide phase is occurring and copper oxide can form. It is known that silver oxide could also form under these conditions and silver oxide has a high solubility in copper oxide (Kohlmeyer and Sprenger, 1948). Furthermore, it is reported that copper oxide can dissolve up to ten mass percent metallic silver (Froehlich, 1932). These effects would increase the silver content of the copper selenide phase and thus lower the distribution ratios. 4.0
3.5
•
Po, = 1.3 x 10.22 arm
O
Po=0.21 atm
•
Po~ = 5 x 10"~atm
--
3.0
,. -.•... ...•"
2.5-
2.0
, •..•'
--
..,• ...~•' ...,.'"
1.5
.,•,"
,. ..•.' 1.0
--
0.,.
Y 0.5
©
O
--
0.0 0.0
I
I
I
0.1
0.2
0.3
0.4
I
I
I
0.5
0.6
0.7
0.8
Ag concentration in Cu-rich phase (mass percent)
Fig. 13 Effect of Ag concentration of the Cu-rich phase on the silver distribution ratio at various oxygen partial pressures at 1177°C.
CONCLUSIONS
(1) Samples o f a copper-rich phase and a copper selenide-rich phase containing silver were equilibrated at temperatures of 1130°C to 1223°C at various oxygen potentials. The oxygen content of the copper-rich liquid reached a relatively constant value but the oxygen content of the copper selenide rich phase continuously increased. The silver content in both phases reached an equilibrium value after two hours. (2) The oxidation of the copper selenide-rich phase resulted in the production of some copper oxide and possibly some copper selenate. The copper oxide formed on the surface of the copper selenide. (3) The oxygen content of both phases at four hours of processing varied with the partial pressure of oxygen as follows:
1456
Effectof oxygenon the Cu-Cu2Se-Agsystem
Ocu.richliqui d = 0.75 + 7.79 x10 -3 log P02 Ocu2Se_richliquid = 1.42 + 4.2 x 10-2 log PO2 The silver distribution ratio was lower at higher oxygen potentials due to the preferential oxidation of the Cu2Se-rich liquid. (4) Nickel additions resulted in a significant increase in the oxygen content of both the copper-rich and the copper selenide-rich phases. Gold increased the oxygen content of the copper selenide rich phase while palladium reduced the oxygen content of the copper-rich liquid.
ACKNOWLEDGEMENTS The authors would like to thank the Natural Sciences and Engineering Research Council of Canada (NSERC) for their support of this research. Dr. P. Lindon of Laurentian University of Sudbury, Ontario is acknowledged for providing the facilities for this research.
REFERENCES
Azuma, K., and Ogawa, Y., Effect of Gold, Silver, Tin and Nickel on the Activity of Oxygen in Liquid Copper, Journal of the Mining and Metallurgical Institute of Japan, 1975, 91(2), 77-82. Babitsyna, A.A., Emelyanova, T.A., Cheritsyna, M.A., and Kalinninkov, V.T., The Copper-Selenium System, Russian Journal of Inorganic Chemistry, 1975, 20 (11), 1711-1713. Burylev, B.P., Fedorova, N.N., and Tsemekhman, L. Sh., Equilibrium Diagrams of The Cu-S, Cu-Se and Cu-Te Systems, Russian Journal oflnorganic Chemistry, 1974, 19(8), 1249-1250. Chen, T.T., and Dutrizac, J.E., A Mineralogical Study of the Deportment and Reaction of Silver during Copper Electrorefining, Metallurgical Transactions B, 1989, 20B (June), 345-361. Chen, T.T., and Dutrizac, J.E., Mineralogical Characterization of Anode Slimes -- Part I. Anode Copper from Inco's Copper Cliff Copper Refinery, Canadian Metallurgical Quarterly, 1989, 27(2), 91-96. Chen, T.T., and Dutrizac, J.E., Mineralogical Characterization of Anode Slimes -- Part II. Raw Anode Slimes from Inco's Copper Cliff Copper Refinery, Canadian Metallurgical Quarterly, 1988, 27(2), 97-116. Chen, T.T., and Dutrizac, J.E., Mineralogical Characterization of Anode Slimes -- Part III. Sulphation Reaction Slimes from Inco's Copper Cliff Copper Refinery, Canadian Metallurgical Quarterly, 1988, 27(2), 107-116. Chen, T.T.; and Dutrizac, J.E., Mineralogical Characterization of Anode Slimes -- Part IV. Copper-Nickel-Antimony Oxide (Kupferglimmer) in CCR Anodes and Anode Slimes, Canadian Metallurgical Quarterly, 1989, 28(2), 127-134. Chen, T.T., and Dutrizac, J.E., Mineralogical Characterization of Anode Slimes -- Part V. Nickel Rich Copper Anodes from the CCR Division of Noranda Minerals Inc., Canadian Metallurgical Quarterly, 1990, 29(1), 27-37. Chen, T.T., and Dutrizac, J.E., Mineralogical Characterization of Anode Slimes -- Part VI. Pressure Leached Slimes from the CCR Division of Noranda Minerals Inc., Canadian Metallurgical Quarterly, 1990, 29(4), 293-305. Chen, T.T., and Dutrizac, J.E., Mineralogical Characterization of Anode Slimes -- Part VII. Copper Anodes and Anode Slimes from the Chuquicamata Division of Codelco-Chile, Canadian Metallurgical Quarterly, 1991, 30(2), 95-106. Chen, T.T., and Dutrizac, J.E., Mineralogical Characterization of Anode Slimes -- Part VIII. Silica in Copper Anodes and Anode Slimes, Canadian Metallurgical Quarterly, 1991, 30(3), 173-185. Chen, T.T., and Dutrizac, J.E., Mineralogical Characterization of Anode Slimes -- Part IX. The Reaction of Kidd Creek Anode Slimes with Various Lixiviants, Canadian Metallurgical Quarterly, 1993, 32(4), 267-279.
M. Lamontagneet al
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