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Solvent extraction of copper from chloride solution I: Extraction isotherms
Hydrometallurgy 137 (2013) 13–17
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Hydrometallurgy journal homepage: www.elsevier.com/locate/hydromet
Solvent extraction of copper from chloride solution I: Extraction isotherms Jianming Lu ⁎, David Dreisinger Department of Materials Engineering, University of British Columbia, 309-6350 Stores Road, Vancouver, BC, Canada, V6T 1Z4
a r t i c l e
i n f o
Article history: Received 19 November 2012 Received in revised form 31 March 2013 Accepted 10 April 2013 Available online 17 April 2013 Keywords: Copper Chloride solution Solvent extraction Extraction isotherm
a b s t r a c t This study was conducted as part of the development of a novel process for copper recovery from chalcopyrite by chloride leaching, simultaneous cuprous oxidation and cupric solvent extraction to transfer copper to a conventional sulfate electrowinning circuit, and hematite precipitation to reject iron. Copper solvent extraction from chloride solution has been studied using four LIX® extractants (LIX84-I, LIX612N-LV, XI-04003 and LIX984N) from BASF with respect to copper extraction as a function of pH and A/O ratio, and behavior of the impurities. At a pH below 0.5, the copper extraction increased quickly with increasing pH while at a pH above 0.5, it increased only slightly with pH. The copper extraction in organic solution was virtually not affected by the impurities. The iron extraction in organic solution increased with decreasing A/O ratio from 2:1 to 1:8 as the copper extraction decreased. Conversely, the Cu/Fe ratio in organic solution increased as copper extraction increased. The extractions of silver and lead were 1 mg/L or lower under all conditions tested. The other impurities (Zn, Ni, Cd, Cr, Hg, As and Sb) were virtually not loaded into the organic solution. The optimum copper solvent extraction conditions in chloride solution were proposed. Crown Copyright © 2013 Published by Elsevier B.V. All rights reserved.
1. Introduction Ferric and/or cupric chloride leaching processes have been extensively studied to treat sulfide concentrates of copper, lead, and zinc (Dutrizac, 1992; Peters, 1977). Chloride leaching has the following advantages over sulfate systems: (1) supporting high metal solubility, (2) enhanced redox behavior, (3) increased rates of leaching, and (4) the formation of predominantly elemental sulfur. In a chloride system, both cuprous and cupric ions are stabilized through complexation with chloride ions. Copper can be efficiently extracted into chloride solution from chalcopyrite and bornite and a copper extraction of 99% can be reached at a temperature below 100 °C using a two-stage countercurrent chloride leach circuit (Lu and Dreisinger, 2013). Compared to the conventional sulfate system, one challenge for the chloride system is to produce high quality copper since some impurities such as silver are not removed efficiently from chloride solution, and dendritic copper cathodes are produced by electrowinning from chloride solution. Generally there are four processes to recover copper from chloride solution: (1) the precipitation of CuCl at lower temperature and reduction to Cu in the UBC-Cominco and the Cymet processes (Dutrizac, 1992; Peters, 1977), (2) direct electrowinning of Cu from chloride solution (Moyes et al., 2000), (3) the precipitation of Cu2O and reduction to Cu with hydrogen (Hyvarinen and Hamalainen, 2005), and (4) solvent extraction of copper to sulfate system from chloride system and electrowinning of copper from
⁎ Corresponding author. Tel.: +1 604 822 1357; fax: +1 604 822 3619. E-mail address: [email protected] (J. Lu).
sulfate media (Demarthe et al., 1976; Liddicoat and Dreisinger, 2007). The first two methods normally result in impure copper while the third one is generally suitable for the solution containing a small amount of iron. The fourth one can generate high purity copper since the impurities are separated from copper by solvent extraction. In this process, the advantages of both chloride (leaching) and sulfate (SX-EW) systems can be fully utilized and their disadvantages can be avoided. The transfer of copper from a Cu(I) chloride solution to a Cu(II) sulfate solution requires extraction with a hydroxyoxime extractant as is used normally in the processing of sulfate-based copper leach solution. The solvent extraction process for copper recovery involves simultaneous cuprous oxidation and cupric solvent extraction: 4 CuCl þ 4 HRðorgÞ þ O2 ¼ 2 CuR2 ðorgÞ þ 2 CuCl2 þ 2H2 O
ð1Þ
This process was first proposed by Demarthe et al. (1976). Proof of concept testing indicated that cuprous oxidation–cupric solvent extraction using air or oxygen was feasible with minimum transfer of impurities. However, reliable data on the kinetics and equilibrium processes for copper extraction is required for process definition. In this work, four LIX® extractants (LIX84-I, LIX612N-LV, XI-04003 and LIX984N) recommended by BASF (Cognis) have been studied since these extractants have a high copper loading capacity and high selectivity of copper over iron. The objective of this study is to develop the equilibrium data for copper solvent extraction from chloride solution for the selection of optimum solvent extraction operating conditions
0304-386X/$ – see front matter. Crown Copyright © 2013 Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.hydromet.2013.04.001
14
J. Lu, D. Dreisinger / Hydrometallurgy 137 (2013) 13–17
point was determined using standard solutions with different concentrations of copper.
2. Experimental 2.1. Apparatus
3. Results and discussion The tests for extraction isotherms were conducted in a 250-mL glass reactor with three baffles and a well at its base to allow collection and pH measurement of aqueous solution (Fig. 1). The pH was measured using an Orion Ross sure-flow pH electrode. 2.2. Experimental procedures The A/O ratio was set at 2:1, 1:1, 1:2, 1:3, 1:4 and 1:8 for investigating extraction isotherms. The procedures for generating an extraction isotherm are as follows: (1) Aqueous solution and organic solution are transferred to the reactor. (2) The aqueous and organic phases are vigorously mixed and the pH is controlled by addition of NaOH. The pH is first adjusted close to a target value using 50% NaOH and then it is finely tuned to the target value using 10% NaOH. (3) When the reaction reaches the equilibrium, the stirring is stopped. After the two phases are separated, the mixed solution is transferred to a separatory funnel. The separated aqueous solution is filtered using Whatman No. 42 filtration paper to remove entrained organic solution. The separated organic solution is centrifuged to remove trapped minor aqueous solution. (4) Loaded organic solution is stripped three times using 6 M HCl solution with an A/O ratio of 1:1. All strip solutions are collected and combined for chemical analysis. 2.3. Preparation of organic and aqueous solution The organic solutions were prepared on a volume basis (40% extractant and 60% Phillips 66 kerosene). The aqueous feed solution for extraction isotherms was prepared using deionized water, reagent grade cupric, calcium and ferric chlorides. The impurities (Zn, Ni, Pb, Cd, Cr, Ag, Hg, Sb) were added as their chlorides while As was added as sodium arsenite. 2.4. Chemical analysis The concentrations of Cu and Fe were analyzed using atomic adsorption. The other elements were analyzed using ICP. The free acid titration was conducted with oxalate masking. 2 M potassium oxalate was used to complex metal ions that would normally contribute protons, via reaction with hydroxide ions in water. The titration end
In the cuprous oxidation–cupric solvent extraction system (CuCl/ CuCl2–FeCl2/FeCl3–CaCl2), without addition of base and acid, the pH is difficult or impossible to control in the A/O ratio range of 2:1 to 1:8. For example, at an A/O ratio of 2:1, after oxidation and extraction of a small part of copper, the pH rises to a high value (>1.0) since copper extraction easily reaches the full copper loading capacity of the organic phase and the amount of H+ released due to Reaction 2 is much less than that consumed due to Reaction 3. At an A/O ratio of 1:8, the pH cannot be raised to 0.5 by the oxidation of Cu(I) and Fe(II) since copper extraction is about one quarter of the full copper loading capacity of the organic phase and the amount of H+ released due to Reaction 2 is much larger than that consumed due to Reaction 3. þ
2þ
Cu ðaqÞ þ 2HRðorgÞ ¼ CuR2 ðorgÞ þ 2H þ
2þ
2 Cu ðFe
þ
2þ
Þ þ 1=2 O2 þ 2H ¼ 2 Cu
ð2Þ 3þ
ðFe
Þ þ H2 O
Not only is Cu(I) oxidized but also some Fe(II) is oxidized. It is difficult to accurately predict the concentrations of Cu(II) and Fe(III) under the conditions studied without very reliable equilibrium constants and activity coefficients of Cu(II)/Cu(I) and Fe(III)/Fe(II) chloride species. The extraction of Fe(III) into the organic phase can affect the copper extraction especially at a high pH. Therefore it is very difficult to develop copper extraction isotherms as a function of pH and Cu concentration (A/O ratio). By careful selection of initial CuCl2 and CaCl2 concentrations, the copper extraction data developed in CuCl2 and CaCl2 system with addition of NaOH for pH control can be applied in a simultaneous cuprous oxidation and cupric solvent extraction process. 3.1. pH measurement Copper extraction in organic solution is dependent on aqueous solution pH. The accurate measurement of aqueous solution pH is important to develop extraction isotherms. When aqueous solution contains a significant amount of copper and calcium chlorides, the activity coefficient of hydrogen ion is significantly changed and the pH measurement is affected. To control the aqueous solution pH, the copper solvent extraction was conducted by addition of NaOH solution into copper chloride solution. The extraction reaction is expressed as: 2HRðorgÞ þ CuCl2 þ 2 NaOH ¼ CuR2 ðorgÞ þ 2 NaCl þ 2 H2 O
Baffle
Ti shaft
pH probe
Baffle
Teflon impeller Fig. 1. A schematic diagram for glass reactor for metal extraction isotherms.
ð3Þ
ð4Þ
With increasing copper extraction, the CuCl2 concentration decreased and the NaCl concentration increased. At a constant H + concentration, the pH changed as copper was extracted into the organic phase. Therefore the pH measurement with respect to H + concentration was conducted in solutions with a constant CaCl2 concentration and different CuCl2 and NaCl concentrations. The initial aqueous solution composition was 1.25 M CuCl2 (~ 80 g/L Cu) and 1.8 M CaCl2. The reason for selection of such an initial aqueous composition is based on the following consideration: when half of the copper was extracted into the organic phase, the ionic strength and the free chloride concentration were close to those in the cuprous oxidation–cupric solvent extraction system (Reaction 1). Therefore the extraction isotherm data developed can be used for the cuprous oxidation and cupric solvent extraction system. In such a concentrated chloride solution, the major Cu(II) species are CuCl2(aq), CuCl3− and CuCl42− while the dominant Fe(II) species is FeCl + (Muir, 2002; Winand, 1991). The ionic strength and free chloride concentrations were
J. Lu, D. Dreisinger / Hydrometallurgy 137 (2013) 13–17
SX reaction
Initial composition
Reaction 1 1.25 M CuCl + 2 M FeCl2 + 1.5 M CaCl2 Reaction 4 1.25 M CuCl2 + 1.8 M CaCl2
Composition after extraction of half Cu
[Cl-]/M Ionic Species selected for strength/ calculation M
0.625 M CuCl2 + 2 M FeCl2 + 1.5 M CaCl2 0.625 M CuCl2 + 1.25 M NaCl + 1.8 M CaCl2
CuCl2 CuCl3− CuCl42− CuCl2 CuCl3− CuCl42−
5.0 6.50 7.13 4.85 6.65 7.28
6.19 4.38 3.75 6.65 4.23 3.6
calculated based on the selection of CuCl2 (aq), CuCl3− and CuCl42− respectively as the sole species present and they are summarized in Table 1. After the extraction of half of the copper, the ionic strength and free chloride concentration for Reaction 1 are close to those for Reaction 4. The pH values measured at 40 °C are summarized in Table 2. The measured pH varied only slightly with changing CuCl2 and NaCl concentrations. There is a virtually linear relationship between pH and free acid concentration, and the slope is 1.00. The HCl concentration was first determined by titration and HCl was added to adjust the HCl concentration to the target value. The concentrations of CuCl2 and CaCl2 were so high that the pH was affected by the liquid junction potential between the filling solution of the reference electrode for the pH probe and the solution studied. The direct measurement of a junction potential is not possible. In this study, the Henderson equation was used to estimate the liquid junction potential (Ej). The liquid junction potential and the corresponding pH correction are summarized in Table 3. As NaOH solution was added and copper was extracted, the aqueous solution was diluted due to addition of the solution and water formed by Reaction 4. The extraction of 25, 50, 75 and 100% copper resulted in around 4, 8, 12, and 16% dilution respectively. The liquid junction potential recalculated considering the dilution factor was around 7.0 mV for all solutions and the pH corrected for liquid junction potential was the pH measured plus 0.11.
Table 3 Liquid junction potential and corresponding pH correction as a function of HCl concentration at different compositions and 40 °C. HCl concentration/M 1.25 M CuCl2 and 1.8 M CaCl2 0.9375 M CuCl2, 0.675 M NaCl and 1.8 M CaCl2 0.625 M CuCl2, 1.25 M NaCl and 1.8 M CaCl2 0.3125 M CuCl2, 1.875 M NaCl and 1.8 M CaCl2 2.49 M NaCl and 1.8 M CaCl2
H+ concentration/M
0.005 0.01 0.02 0.04 0.08
1.25 M CuCl2 and 1.8 M CaCl2 0.9375 M CuCl2, 0.675 M NaCl and 1.8 M CaCl2 0.625 M CuCl2, 1.25 M NaCl and 1.8 M CaCl2 0.3125 M CuCl2, 1.875 M NaCl and 1.8 M CaCl2 2.49 M NaCl and 1.8 M CaCl2a
1.20 1.18 1.16 1.14 1.09
0.90 0.88 0.85 0.84 0.80
0.60 0.58 0.56 0.54 0.49
0.31 0.27 0.26 0.24 0.19
0.01 −0.01 −0.02 −0.03 −0.06
a Instead of 2.5 M NaCl, 2.49 M NaCl was used because the saturation concentration of NaCl in 1.8 CaCl2 solution is 2.49 M.
0.01
0.02
0.04
0.08
7.0 0.11 7.7 0.12 8.3 0.13 8.8 0.14 9.3 0.15
6.8 0.11 7.5 0.12 8.1 0.13 8.7 0.14 9.2 0.15
6.4 0.10 7.1 0.12 7.8 0.13 8.4 0.14 8.9 0.14
5.7 0.09 6.5 0.10 7.2 0.12 7.8 0.13 8.4 0.13
20
LIX84-I LIX612N-LV XI-04003 LIX984N
15
10 0.0
0.5
1.0
1.5
Measured pH Fig. 2. Copper extraction pH isotherm in chloride solution based on the analysis of the aqueous and organic solutions at 40 °C and A/O ratio of 1.
25
[Cu2+]org. / g L-1
Table 2 pH values as a function of HCl concentration at different compositions at 40 °C.
0.005 7.1 0.11 7.7 0.12 8.3 0.13 8.9 0.14 9.4 0.15
25
3.2. Copper extraction pH isotherms Four LIX extractants (LIX84-I, LIX612N-LV, XI-04003 and LIX984N) from BASF were tested. LIX 84-I is based on ketoxime. LIX 984 N is a 50:50 mixture of LIX 860 N-I (C9 aldoxime) with LIX 84-I. XI04003 is formulated with C12 aldoxime and LIX 612 N-LV is formulated with C9 aldoxime. Both XI04003 and LIX612n-LV are formulated with a ketone as a modifier to the same degree of modification. If properly formulated, they should give identical performance within the limits of error of the experiment. When the feed aqueous solution and organic solution were mixed, the aqueous solution pH decreased from 0.86 to the values ranging between −0.3 and −0.6, which were dependent on the A/O ratio and the type of organic extractant. A lower A/O ratio resulted in a lower pH since more copper was extracted into the organic phase and more acid was produced. A stronger extractant resulted in a lower pH.
Ej/mV ΔpH Ej/mV ΔpH Ej/mV ΔpH Ej/mV ΔpH Ej/mV ΔpH
At pH − 0.6 to − 0.3, the copper extraction was only 20–40% of their full loading capacity. NaOH was added to adjust the pH to the target value and the extraction reaction is expressed by Reaction 4. The plot of copper extraction against pH is shown in Fig. 2. At a pH below 0.5, the copper extraction increased quickly with increasing pH. At a pH above 0.5, the copper extraction increased slowly with increasing pH, indicating that the copper extraction was close to the full capacity of the extractant. The copper extraction calculated based on the H + generated (shown in Fig. 3) was very close to that based on
[Cu2+]org. / g L-1
Table 1 Ionic strength and free chloride concentration after extraction of half the copper.
15
20
LIX84-I LIX612N-LV 15
XI-04003 LIX984N
10 0.0
0.5
1.0
1.5
Measured pH Fig. 3. Copper extraction pH isotherms in chloride solution based on the H+ generated at 40 °C and A/O ratio of 1.
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J. Lu, D. Dreisinger / Hydrometallurgy 137 (2013) 13–17
25
Table 4 Composition of aqueous feed solution (g/L).
[Cu2+]org. / g L-1
20
Cu
Fe
Zn
Pb
Ni
Cd
Cr
Hg
Ag
As
Sb
75.6
9.78
1.95
0.918
0.906
1.02
0.101
0.173
0.046
0.052
0.061
15
3.4. Behavior of impurities in copper solvent extraction 10
LIX84-I LIX612N-LV XI04003 LIX984N
5
0 0
20
40
60
80
[Cu2+]aq. / g L-1 Fig. 4. Copper extraction distribution isotherms from chloride solution based on the analysis of the aqueous and organic solutions at 40 °C and pH 0.50.
the analysis, indicating that the extraction reaction follows Reaction 4. The copper extraction for XI04003 was 0.5–1.0% lower than that for LIX612N-LV probably due to small differences in extractant reagent concentrations and analysis.
The behavior of impurities is important to know. Fe, Zn, Ni, Pb, Ni, Cd, Cr, Hg, Ag, As and Sb were added as impurities. The feed solution composition is summarized in Table 4. Copper and iron extraction distribution isotherms are shown in Figs. 6 and 7 respectively. The copper extraction was nearly not affected by the impurities by comparison of Figs. 4 and 6. The iron concentration in the organic solution decreased with increasing iron concentration in the aqueous solution (or decreasing A/O ratio from 2:1 to 1:8). At a higher A/O ratio, the organic solution was loaded with more copper and therefore less iron was extracted into the organic solution. To suppress the iron extraction in the organic solution, the copper concentration in the organic solution should be close to its full loading capacity. The Cu/Fe ratios in the organic solution at different A/O ratios are summarized in Table 5. The Cu/Fe ratios decreased with decreasing A/O ratios as the copper concentration decreased and more iron was extracted. The selectivity of copper over iron is related not only to the extractant own properties, but also to the pH and copper extraction in organic solution. A lower pH and high copper extraction
3.3. Copper extraction distribution isotherms 25
20
[Cu2+]org. / g L-1
At a pH above 0.5, the copper extraction increased slowly with increasing pH. At a pH above 0.9, iron oxide or hydroxide began to precipitate from the solution with 20 g/L Fe as FeCl3, 1.25 M CuCl2 and 1.8 M CaCl2. For cuprous oxidation–cupric solvent extraction, when most of Cu(I) is oxidized to Cu(II), a small amount of iron exists in the form of Fe(III) since in such a concentrated chloride medium, the redox potential for Cu(II)/Cu(I) is close to that for Fe(III)/Fe(II). To avoid the precipitation of iron oxide and obtain a higher copper extraction, the pH should be controlled around 0.5. Therefore copper extraction distribution isotherms were developed at pH 0.5 and they are shown in Fig. 4. At a low copper concentration (below 10 g/L) in aqueous solution, the copper extraction in the organic solution increased rapidly with increasing aqueous copper concentration. As more copper was extracted into the organic solution, the copper concentration in the organic solution increased slowly with increasing aqueous copper concentration. The copper extraction calculated based on the H + generated (shown in Fig. 5) was very close to that based on the analysis of the organic solution.
LIX84-I LIX612N-LV XI04003 LIX984N
10
5
0 0
20
40
60
80
[Cu2+]aq. / g L-1 Fig. 6. Copper extraction distribution isotherms at 40 °C and pH 0.50.
25
0.6
LIX84-I LIX612N-LV XI04003 LIX984N
0.5
[Fe3+]org. / g L-1
20
[Cu2+]org. / g L-1
15
15
10
LIX84-I LIX612N-LV XI04003 LIX984N
5
20
40
[Cu2+]aq.
60
/g
0.3 0.2 0.1
0 0
0.4
80
L-1
0 4
5
6
7
[Fe3+]aq. Fig. 5. Copper extraction distribution isotherms in chloride solution based on the H+ generated at 40 °C and pH 0.50.
8
/g
9
10
L-1
Fig. 7. Iron extraction distribution isotherms in chloride solution at 40 °C and pH 0.50.
J. Lu, D. Dreisinger / Hydrometallurgy 137 (2013) 13–17 Table 5 [Cu]/[Fe] ratios in organic solution at different A/O ratios. A/O ratio
2:1
1:1
1:2
1:4
1:8
LIX84-I LIX612N-LV XI-04003 LIX984N
225 285 295 266
218 272 285 253
178 201 226 191
90 94 94 54
23 20 20 16
result in a lower iron extraction. The extractions of silver and lead were 1 mg/L or lower for all five extractants. The behavior of these impurities in copper solvent extraction is probably related to the formation of their chloro-complexes that are not extracted into hydroxyoxime organic solution. 4. Conclusions There is a virtually linear relationship between pH and free acid concentration (0.005–0.08 M) in CuCl2–NaCl–CaCl2 solution and the slope is 1.00. Considering the dilution due to the addition of NaOH solution, the liquid junction potential estimated using Henderson's equation is around 7 mV for all solutions and the corrected pH is the measured value plus 0.11. At a pH below 0.5, the copper extraction increased quickly with increasing pH while at a pH above 0.5, it only increased slowly with increasing pH. At an aqueous copper concentration below 10 g/L, the copper extraction increased quickly with increasing aqueous copper concentration while at an aqueous copper concentration above 10 g/L, the copper extraction increased slowly with increasing aqueous copper concentration. The loading capacity order of copper for four extractants is: LIX984N > LIX612N-LV, XI04003 > LIX84-I. The copper extraction in organic solution was virtually not affected by impurities except for Fe(III). The iron extraction in the organic solution increased with decreasing copper extraction. The Cu/Fe ratio in the organic solution increased with increasing copper extraction as iron extraction decreased. The selectivity of copper over iron is related not
17
only to the extractant own properties, but also to the pH and copper extraction in organic solution. The extractions of silver and lead were 1 mg/L or lower. The other impurities (Zn, Ni, Cd, Cr, Hg, As and Sb) were virtually not loaded into the organic solution. The recommended operating conditions are as follows: (1) pH should be controlled around 0.5 to maintain a high copper extraction and a low iron extraction, and prevent the precipitation of ferric hydroxide at a higher pH; and (2) copper extraction should be close to its full loading capacity to suppress iron extraction and maintain a high Cu/Fe ratio in organic solution.
Acknowledgments The authors would like to thank Falconbridge Limited (now XSTRATA) for funding this project and allowing for publication, and also thank BASF (Cognis) for supplying the solvents.
References Demarthe, J.M., Gandon, L., Georgeaux, A., 1976. A new hydrometallurgy process for copper. In: Yannopoulos, J.C., Agarwal, J.C. (Eds.), Extractive Metallurgy of Copper. TMS, AIME, New York, pp. 825–848. Dutrizac, J.E., 1992. The leaching of sulfide minerals in chloride media. Hydrometallurgy 29, 1–45. Hyvarinen, O., Hamalainen, M., 2005. HydroCopper™ — a new technology producing copper directly from concentrate. Hydrometallurgy 77, 61–65. Liddicoat, J., Dreisinger, D., 2007. Chloride leaching for chalcopyrite. Hydrometallurgy 89, 323–331. Lu, J., Dreisinger, D., 2013. Copper chloride leaching from chalcopyrite concentrate. Miner. Eng. 45, 185–190. Moyes, J., Houllis, F., Bhappu, R.R., 2000. The Intec copper process demonstration plant. 5th Annual Copper Hydromet Roundtable '99 International Conference; Phoenix, AZ; USA; 10 Oct. 1999. Randol International, pp. 65–72. Muir, D.M., 2002. Basic principles of chloride hydrometallurgy. In: Peek, E., Weert, G.V. (Eds.), Chloride Metallurgy 2002, Vol. II. Metallurgical Society of CIM, Montreal, pp. 759–791. Peters, E., 1977. Applications of chloride hydrometallurgy to treatment of sulfide minerals. Chloride Hydrometallurgy. Benelux Metallurgie, Brussels, pp. 1–37. Winand, R., 1991. Chloride hydrometallurgy. Hydrometallurgy 27 (1991), 285–316.
Contents lists available at SciVerse ScienceDirect
Hydrometallurgy journal homepage: www.elsevier.com/locate/hydromet
Solvent extraction of copper from chloride solution I: Extraction isotherms Jianming Lu ⁎, David Dreisinger Department of Materials Engineering, University of British Columbia, 309-6350 Stores Road, Vancouver, BC, Canada, V6T 1Z4
a r t i c l e
i n f o
Article history: Received 19 November 2012 Received in revised form 31 March 2013 Accepted 10 April 2013 Available online 17 April 2013 Keywords: Copper Chloride solution Solvent extraction Extraction isotherm
a b s t r a c t This study was conducted as part of the development of a novel process for copper recovery from chalcopyrite by chloride leaching, simultaneous cuprous oxidation and cupric solvent extraction to transfer copper to a conventional sulfate electrowinning circuit, and hematite precipitation to reject iron. Copper solvent extraction from chloride solution has been studied using four LIX® extractants (LIX84-I, LIX612N-LV, XI-04003 and LIX984N) from BASF with respect to copper extraction as a function of pH and A/O ratio, and behavior of the impurities. At a pH below 0.5, the copper extraction increased quickly with increasing pH while at a pH above 0.5, it increased only slightly with pH. The copper extraction in organic solution was virtually not affected by the impurities. The iron extraction in organic solution increased with decreasing A/O ratio from 2:1 to 1:8 as the copper extraction decreased. Conversely, the Cu/Fe ratio in organic solution increased as copper extraction increased. The extractions of silver and lead were 1 mg/L or lower under all conditions tested. The other impurities (Zn, Ni, Cd, Cr, Hg, As and Sb) were virtually not loaded into the organic solution. The optimum copper solvent extraction conditions in chloride solution were proposed. Crown Copyright © 2013 Published by Elsevier B.V. All rights reserved.
1. Introduction Ferric and/or cupric chloride leaching processes have been extensively studied to treat sulfide concentrates of copper, lead, and zinc (Dutrizac, 1992; Peters, 1977). Chloride leaching has the following advantages over sulfate systems: (1) supporting high metal solubility, (2) enhanced redox behavior, (3) increased rates of leaching, and (4) the formation of predominantly elemental sulfur. In a chloride system, both cuprous and cupric ions are stabilized through complexation with chloride ions. Copper can be efficiently extracted into chloride solution from chalcopyrite and bornite and a copper extraction of 99% can be reached at a temperature below 100 °C using a two-stage countercurrent chloride leach circuit (Lu and Dreisinger, 2013). Compared to the conventional sulfate system, one challenge for the chloride system is to produce high quality copper since some impurities such as silver are not removed efficiently from chloride solution, and dendritic copper cathodes are produced by electrowinning from chloride solution. Generally there are four processes to recover copper from chloride solution: (1) the precipitation of CuCl at lower temperature and reduction to Cu in the UBC-Cominco and the Cymet processes (Dutrizac, 1992; Peters, 1977), (2) direct electrowinning of Cu from chloride solution (Moyes et al., 2000), (3) the precipitation of Cu2O and reduction to Cu with hydrogen (Hyvarinen and Hamalainen, 2005), and (4) solvent extraction of copper to sulfate system from chloride system and electrowinning of copper from
⁎ Corresponding author. Tel.: +1 604 822 1357; fax: +1 604 822 3619. E-mail address: [email protected] (J. Lu).
sulfate media (Demarthe et al., 1976; Liddicoat and Dreisinger, 2007). The first two methods normally result in impure copper while the third one is generally suitable for the solution containing a small amount of iron. The fourth one can generate high purity copper since the impurities are separated from copper by solvent extraction. In this process, the advantages of both chloride (leaching) and sulfate (SX-EW) systems can be fully utilized and their disadvantages can be avoided. The transfer of copper from a Cu(I) chloride solution to a Cu(II) sulfate solution requires extraction with a hydroxyoxime extractant as is used normally in the processing of sulfate-based copper leach solution. The solvent extraction process for copper recovery involves simultaneous cuprous oxidation and cupric solvent extraction: 4 CuCl þ 4 HRðorgÞ þ O2 ¼ 2 CuR2 ðorgÞ þ 2 CuCl2 þ 2H2 O
ð1Þ
This process was first proposed by Demarthe et al. (1976). Proof of concept testing indicated that cuprous oxidation–cupric solvent extraction using air or oxygen was feasible with minimum transfer of impurities. However, reliable data on the kinetics and equilibrium processes for copper extraction is required for process definition. In this work, four LIX® extractants (LIX84-I, LIX612N-LV, XI-04003 and LIX984N) recommended by BASF (Cognis) have been studied since these extractants have a high copper loading capacity and high selectivity of copper over iron. The objective of this study is to develop the equilibrium data for copper solvent extraction from chloride solution for the selection of optimum solvent extraction operating conditions
0304-386X/$ – see front matter. Crown Copyright © 2013 Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.hydromet.2013.04.001
14
J. Lu, D. Dreisinger / Hydrometallurgy 137 (2013) 13–17
point was determined using standard solutions with different concentrations of copper.
2. Experimental 2.1. Apparatus
3. Results and discussion The tests for extraction isotherms were conducted in a 250-mL glass reactor with three baffles and a well at its base to allow collection and pH measurement of aqueous solution (Fig. 1). The pH was measured using an Orion Ross sure-flow pH electrode. 2.2. Experimental procedures The A/O ratio was set at 2:1, 1:1, 1:2, 1:3, 1:4 and 1:8 for investigating extraction isotherms. The procedures for generating an extraction isotherm are as follows: (1) Aqueous solution and organic solution are transferred to the reactor. (2) The aqueous and organic phases are vigorously mixed and the pH is controlled by addition of NaOH. The pH is first adjusted close to a target value using 50% NaOH and then it is finely tuned to the target value using 10% NaOH. (3) When the reaction reaches the equilibrium, the stirring is stopped. After the two phases are separated, the mixed solution is transferred to a separatory funnel. The separated aqueous solution is filtered using Whatman No. 42 filtration paper to remove entrained organic solution. The separated organic solution is centrifuged to remove trapped minor aqueous solution. (4) Loaded organic solution is stripped three times using 6 M HCl solution with an A/O ratio of 1:1. All strip solutions are collected and combined for chemical analysis. 2.3. Preparation of organic and aqueous solution The organic solutions were prepared on a volume basis (40% extractant and 60% Phillips 66 kerosene). The aqueous feed solution for extraction isotherms was prepared using deionized water, reagent grade cupric, calcium and ferric chlorides. The impurities (Zn, Ni, Pb, Cd, Cr, Ag, Hg, Sb) were added as their chlorides while As was added as sodium arsenite. 2.4. Chemical analysis The concentrations of Cu and Fe were analyzed using atomic adsorption. The other elements were analyzed using ICP. The free acid titration was conducted with oxalate masking. 2 M potassium oxalate was used to complex metal ions that would normally contribute protons, via reaction with hydroxide ions in water. The titration end
In the cuprous oxidation–cupric solvent extraction system (CuCl/ CuCl2–FeCl2/FeCl3–CaCl2), without addition of base and acid, the pH is difficult or impossible to control in the A/O ratio range of 2:1 to 1:8. For example, at an A/O ratio of 2:1, after oxidation and extraction of a small part of copper, the pH rises to a high value (>1.0) since copper extraction easily reaches the full copper loading capacity of the organic phase and the amount of H+ released due to Reaction 2 is much less than that consumed due to Reaction 3. At an A/O ratio of 1:8, the pH cannot be raised to 0.5 by the oxidation of Cu(I) and Fe(II) since copper extraction is about one quarter of the full copper loading capacity of the organic phase and the amount of H+ released due to Reaction 2 is much larger than that consumed due to Reaction 3. þ
2þ
Cu ðaqÞ þ 2HRðorgÞ ¼ CuR2 ðorgÞ þ 2H þ
2þ
2 Cu ðFe
þ
2þ
Þ þ 1=2 O2 þ 2H ¼ 2 Cu
ð2Þ 3þ
ðFe
Þ þ H2 O
Not only is Cu(I) oxidized but also some Fe(II) is oxidized. It is difficult to accurately predict the concentrations of Cu(II) and Fe(III) under the conditions studied without very reliable equilibrium constants and activity coefficients of Cu(II)/Cu(I) and Fe(III)/Fe(II) chloride species. The extraction of Fe(III) into the organic phase can affect the copper extraction especially at a high pH. Therefore it is very difficult to develop copper extraction isotherms as a function of pH and Cu concentration (A/O ratio). By careful selection of initial CuCl2 and CaCl2 concentrations, the copper extraction data developed in CuCl2 and CaCl2 system with addition of NaOH for pH control can be applied in a simultaneous cuprous oxidation and cupric solvent extraction process. 3.1. pH measurement Copper extraction in organic solution is dependent on aqueous solution pH. The accurate measurement of aqueous solution pH is important to develop extraction isotherms. When aqueous solution contains a significant amount of copper and calcium chlorides, the activity coefficient of hydrogen ion is significantly changed and the pH measurement is affected. To control the aqueous solution pH, the copper solvent extraction was conducted by addition of NaOH solution into copper chloride solution. The extraction reaction is expressed as: 2HRðorgÞ þ CuCl2 þ 2 NaOH ¼ CuR2 ðorgÞ þ 2 NaCl þ 2 H2 O
Baffle
Ti shaft
pH probe
Baffle
Teflon impeller Fig. 1. A schematic diagram for glass reactor for metal extraction isotherms.
ð3Þ
ð4Þ
With increasing copper extraction, the CuCl2 concentration decreased and the NaCl concentration increased. At a constant H + concentration, the pH changed as copper was extracted into the organic phase. Therefore the pH measurement with respect to H + concentration was conducted in solutions with a constant CaCl2 concentration and different CuCl2 and NaCl concentrations. The initial aqueous solution composition was 1.25 M CuCl2 (~ 80 g/L Cu) and 1.8 M CaCl2. The reason for selection of such an initial aqueous composition is based on the following consideration: when half of the copper was extracted into the organic phase, the ionic strength and the free chloride concentration were close to those in the cuprous oxidation–cupric solvent extraction system (Reaction 1). Therefore the extraction isotherm data developed can be used for the cuprous oxidation and cupric solvent extraction system. In such a concentrated chloride solution, the major Cu(II) species are CuCl2(aq), CuCl3− and CuCl42− while the dominant Fe(II) species is FeCl + (Muir, 2002; Winand, 1991). The ionic strength and free chloride concentrations were
J. Lu, D. Dreisinger / Hydrometallurgy 137 (2013) 13–17
SX reaction
Initial composition
Reaction 1 1.25 M CuCl + 2 M FeCl2 + 1.5 M CaCl2 Reaction 4 1.25 M CuCl2 + 1.8 M CaCl2
Composition after extraction of half Cu
[Cl-]/M Ionic Species selected for strength/ calculation M
0.625 M CuCl2 + 2 M FeCl2 + 1.5 M CaCl2 0.625 M CuCl2 + 1.25 M NaCl + 1.8 M CaCl2
CuCl2 CuCl3− CuCl42− CuCl2 CuCl3− CuCl42−
5.0 6.50 7.13 4.85 6.65 7.28
6.19 4.38 3.75 6.65 4.23 3.6
calculated based on the selection of CuCl2 (aq), CuCl3− and CuCl42− respectively as the sole species present and they are summarized in Table 1. After the extraction of half of the copper, the ionic strength and free chloride concentration for Reaction 1 are close to those for Reaction 4. The pH values measured at 40 °C are summarized in Table 2. The measured pH varied only slightly with changing CuCl2 and NaCl concentrations. There is a virtually linear relationship between pH and free acid concentration, and the slope is 1.00. The HCl concentration was first determined by titration and HCl was added to adjust the HCl concentration to the target value. The concentrations of CuCl2 and CaCl2 were so high that the pH was affected by the liquid junction potential between the filling solution of the reference electrode for the pH probe and the solution studied. The direct measurement of a junction potential is not possible. In this study, the Henderson equation was used to estimate the liquid junction potential (Ej). The liquid junction potential and the corresponding pH correction are summarized in Table 3. As NaOH solution was added and copper was extracted, the aqueous solution was diluted due to addition of the solution and water formed by Reaction 4. The extraction of 25, 50, 75 and 100% copper resulted in around 4, 8, 12, and 16% dilution respectively. The liquid junction potential recalculated considering the dilution factor was around 7.0 mV for all solutions and the pH corrected for liquid junction potential was the pH measured plus 0.11.
Table 3 Liquid junction potential and corresponding pH correction as a function of HCl concentration at different compositions and 40 °C. HCl concentration/M 1.25 M CuCl2 and 1.8 M CaCl2 0.9375 M CuCl2, 0.675 M NaCl and 1.8 M CaCl2 0.625 M CuCl2, 1.25 M NaCl and 1.8 M CaCl2 0.3125 M CuCl2, 1.875 M NaCl and 1.8 M CaCl2 2.49 M NaCl and 1.8 M CaCl2
H+ concentration/M
0.005 0.01 0.02 0.04 0.08
1.25 M CuCl2 and 1.8 M CaCl2 0.9375 M CuCl2, 0.675 M NaCl and 1.8 M CaCl2 0.625 M CuCl2, 1.25 M NaCl and 1.8 M CaCl2 0.3125 M CuCl2, 1.875 M NaCl and 1.8 M CaCl2 2.49 M NaCl and 1.8 M CaCl2a
1.20 1.18 1.16 1.14 1.09
0.90 0.88 0.85 0.84 0.80
0.60 0.58 0.56 0.54 0.49
0.31 0.27 0.26 0.24 0.19
0.01 −0.01 −0.02 −0.03 −0.06
a Instead of 2.5 M NaCl, 2.49 M NaCl was used because the saturation concentration of NaCl in 1.8 CaCl2 solution is 2.49 M.
0.01
0.02
0.04
0.08
7.0 0.11 7.7 0.12 8.3 0.13 8.8 0.14 9.3 0.15
6.8 0.11 7.5 0.12 8.1 0.13 8.7 0.14 9.2 0.15
6.4 0.10 7.1 0.12 7.8 0.13 8.4 0.14 8.9 0.14
5.7 0.09 6.5 0.10 7.2 0.12 7.8 0.13 8.4 0.13
20
LIX84-I LIX612N-LV XI-04003 LIX984N
15
10 0.0
0.5
1.0
1.5
Measured pH Fig. 2. Copper extraction pH isotherm in chloride solution based on the analysis of the aqueous and organic solutions at 40 °C and A/O ratio of 1.
25
[Cu2+]org. / g L-1
Table 2 pH values as a function of HCl concentration at different compositions at 40 °C.
0.005 7.1 0.11 7.7 0.12 8.3 0.13 8.9 0.14 9.4 0.15
25
3.2. Copper extraction pH isotherms Four LIX extractants (LIX84-I, LIX612N-LV, XI-04003 and LIX984N) from BASF were tested. LIX 84-I is based on ketoxime. LIX 984 N is a 50:50 mixture of LIX 860 N-I (C9 aldoxime) with LIX 84-I. XI04003 is formulated with C12 aldoxime and LIX 612 N-LV is formulated with C9 aldoxime. Both XI04003 and LIX612n-LV are formulated with a ketone as a modifier to the same degree of modification. If properly formulated, they should give identical performance within the limits of error of the experiment. When the feed aqueous solution and organic solution were mixed, the aqueous solution pH decreased from 0.86 to the values ranging between −0.3 and −0.6, which were dependent on the A/O ratio and the type of organic extractant. A lower A/O ratio resulted in a lower pH since more copper was extracted into the organic phase and more acid was produced. A stronger extractant resulted in a lower pH.
Ej/mV ΔpH Ej/mV ΔpH Ej/mV ΔpH Ej/mV ΔpH Ej/mV ΔpH
At pH − 0.6 to − 0.3, the copper extraction was only 20–40% of their full loading capacity. NaOH was added to adjust the pH to the target value and the extraction reaction is expressed by Reaction 4. The plot of copper extraction against pH is shown in Fig. 2. At a pH below 0.5, the copper extraction increased quickly with increasing pH. At a pH above 0.5, the copper extraction increased slowly with increasing pH, indicating that the copper extraction was close to the full capacity of the extractant. The copper extraction calculated based on the H + generated (shown in Fig. 3) was very close to that based on
[Cu2+]org. / g L-1
Table 1 Ionic strength and free chloride concentration after extraction of half the copper.
15
20
LIX84-I LIX612N-LV 15
XI-04003 LIX984N
10 0.0
0.5
1.0
1.5
Measured pH Fig. 3. Copper extraction pH isotherms in chloride solution based on the H+ generated at 40 °C and A/O ratio of 1.
16
J. Lu, D. Dreisinger / Hydrometallurgy 137 (2013) 13–17
25
Table 4 Composition of aqueous feed solution (g/L).
[Cu2+]org. / g L-1
20
Cu
Fe
Zn
Pb
Ni
Cd
Cr
Hg
Ag
As
Sb
75.6
9.78
1.95
0.918
0.906
1.02
0.101
0.173
0.046
0.052
0.061
15
3.4. Behavior of impurities in copper solvent extraction 10
LIX84-I LIX612N-LV XI04003 LIX984N
5
0 0
20
40
60
80
[Cu2+]aq. / g L-1 Fig. 4. Copper extraction distribution isotherms from chloride solution based on the analysis of the aqueous and organic solutions at 40 °C and pH 0.50.
the analysis, indicating that the extraction reaction follows Reaction 4. The copper extraction for XI04003 was 0.5–1.0% lower than that for LIX612N-LV probably due to small differences in extractant reagent concentrations and analysis.
The behavior of impurities is important to know. Fe, Zn, Ni, Pb, Ni, Cd, Cr, Hg, Ag, As and Sb were added as impurities. The feed solution composition is summarized in Table 4. Copper and iron extraction distribution isotherms are shown in Figs. 6 and 7 respectively. The copper extraction was nearly not affected by the impurities by comparison of Figs. 4 and 6. The iron concentration in the organic solution decreased with increasing iron concentration in the aqueous solution (or decreasing A/O ratio from 2:1 to 1:8). At a higher A/O ratio, the organic solution was loaded with more copper and therefore less iron was extracted into the organic solution. To suppress the iron extraction in the organic solution, the copper concentration in the organic solution should be close to its full loading capacity. The Cu/Fe ratios in the organic solution at different A/O ratios are summarized in Table 5. The Cu/Fe ratios decreased with decreasing A/O ratios as the copper concentration decreased and more iron was extracted. The selectivity of copper over iron is related not only to the extractant own properties, but also to the pH and copper extraction in organic solution. A lower pH and high copper extraction
3.3. Copper extraction distribution isotherms 25
20
[Cu2+]org. / g L-1
At a pH above 0.5, the copper extraction increased slowly with increasing pH. At a pH above 0.9, iron oxide or hydroxide began to precipitate from the solution with 20 g/L Fe as FeCl3, 1.25 M CuCl2 and 1.8 M CaCl2. For cuprous oxidation–cupric solvent extraction, when most of Cu(I) is oxidized to Cu(II), a small amount of iron exists in the form of Fe(III) since in such a concentrated chloride medium, the redox potential for Cu(II)/Cu(I) is close to that for Fe(III)/Fe(II). To avoid the precipitation of iron oxide and obtain a higher copper extraction, the pH should be controlled around 0.5. Therefore copper extraction distribution isotherms were developed at pH 0.5 and they are shown in Fig. 4. At a low copper concentration (below 10 g/L) in aqueous solution, the copper extraction in the organic solution increased rapidly with increasing aqueous copper concentration. As more copper was extracted into the organic solution, the copper concentration in the organic solution increased slowly with increasing aqueous copper concentration. The copper extraction calculated based on the H + generated (shown in Fig. 5) was very close to that based on the analysis of the organic solution.
LIX84-I LIX612N-LV XI04003 LIX984N
10
5
0 0
20
40
60
80
[Cu2+]aq. / g L-1 Fig. 6. Copper extraction distribution isotherms at 40 °C and pH 0.50.
25
0.6
LIX84-I LIX612N-LV XI04003 LIX984N
0.5
[Fe3+]org. / g L-1
20
[Cu2+]org. / g L-1
15
15
10
LIX84-I LIX612N-LV XI04003 LIX984N
5
20
40
[Cu2+]aq.
60
/g
0.3 0.2 0.1
0 0
0.4
80
L-1
0 4
5
6
7
[Fe3+]aq. Fig. 5. Copper extraction distribution isotherms in chloride solution based on the H+ generated at 40 °C and pH 0.50.
8
/g
9
10
L-1
Fig. 7. Iron extraction distribution isotherms in chloride solution at 40 °C and pH 0.50.
J. Lu, D. Dreisinger / Hydrometallurgy 137 (2013) 13–17 Table 5 [Cu]/[Fe] ratios in organic solution at different A/O ratios. A/O ratio
2:1
1:1
1:2
1:4
1:8
LIX84-I LIX612N-LV XI-04003 LIX984N
225 285 295 266
218 272 285 253
178 201 226 191
90 94 94 54
23 20 20 16
result in a lower iron extraction. The extractions of silver and lead were 1 mg/L or lower for all five extractants. The behavior of these impurities in copper solvent extraction is probably related to the formation of their chloro-complexes that are not extracted into hydroxyoxime organic solution. 4. Conclusions There is a virtually linear relationship between pH and free acid concentration (0.005–0.08 M) in CuCl2–NaCl–CaCl2 solution and the slope is 1.00. Considering the dilution due to the addition of NaOH solution, the liquid junction potential estimated using Henderson's equation is around 7 mV for all solutions and the corrected pH is the measured value plus 0.11. At a pH below 0.5, the copper extraction increased quickly with increasing pH while at a pH above 0.5, it only increased slowly with increasing pH. At an aqueous copper concentration below 10 g/L, the copper extraction increased quickly with increasing aqueous copper concentration while at an aqueous copper concentration above 10 g/L, the copper extraction increased slowly with increasing aqueous copper concentration. The loading capacity order of copper for four extractants is: LIX984N > LIX612N-LV, XI04003 > LIX84-I. The copper extraction in organic solution was virtually not affected by impurities except for Fe(III). The iron extraction in the organic solution increased with decreasing copper extraction. The Cu/Fe ratio in the organic solution increased with increasing copper extraction as iron extraction decreased. The selectivity of copper over iron is related not
17
only to the extractant own properties, but also to the pH and copper extraction in organic solution. The extractions of silver and lead were 1 mg/L or lower. The other impurities (Zn, Ni, Cd, Cr, Hg, As and Sb) were virtually not loaded into the organic solution. The recommended operating conditions are as follows: (1) pH should be controlled around 0.5 to maintain a high copper extraction and a low iron extraction, and prevent the precipitation of ferric hydroxide at a higher pH; and (2) copper extraction should be close to its full loading capacity to suppress iron extraction and maintain a high Cu/Fe ratio in organic solution.
Acknowledgments The authors would like to thank Falconbridge Limited (now XSTRATA) for funding this project and allowing for publication, and also thank BASF (Cognis) for supplying the solvents.
References Demarthe, J.M., Gandon, L., Georgeaux, A., 1976. A new hydrometallurgy process for copper. In: Yannopoulos, J.C., Agarwal, J.C. (Eds.), Extractive Metallurgy of Copper. TMS, AIME, New York, pp. 825–848. Dutrizac, J.E., 1992. The leaching of sulfide minerals in chloride media. Hydrometallurgy 29, 1–45. Hyvarinen, O., Hamalainen, M., 2005. HydroCopper™ — a new technology producing copper directly from concentrate. Hydrometallurgy 77, 61–65. Liddicoat, J., Dreisinger, D., 2007. Chloride leaching for chalcopyrite. Hydrometallurgy 89, 323–331. Lu, J., Dreisinger, D., 2013. Copper chloride leaching from chalcopyrite concentrate. Miner. Eng. 45, 185–190. Moyes, J., Houllis, F., Bhappu, R.R., 2000. The Intec copper process demonstration plant. 5th Annual Copper Hydromet Roundtable '99 International Conference; Phoenix, AZ; USA; 10 Oct. 1999. Randol International, pp. 65–72. Muir, D.M., 2002. Basic principles of chloride hydrometallurgy. In: Peek, E., Weert, G.V. (Eds.), Chloride Metallurgy 2002, Vol. II. Metallurgical Society of CIM, Montreal, pp. 759–791. Peters, E., 1977. Applications of chloride hydrometallurgy to treatment of sulfide minerals. Chloride Hydrometallurgy. Benelux Metallurgie, Brussels, pp. 1–37. Winand, R., 1991. Chloride hydrometallurgy. Hydrometallurgy 27 (1991), 285–316.