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Chloride leaching of chalcopyrite
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Hydrometallurgy 89 (2007) 323 – 331 www.elsevier.com/locate/hydromet
Chloride leaching of chalcopyrite J. Liddicoat, D. Dreisinger ⁎ University of British Columbia, Department Metals and Materials Engineering, Vancouver, BC, Canada V6T 1Z4 Received 20 October 2006; received in revised form 7 August 2007; accepted 9 August 2007 Available online 17 August 2007
Abstract Two new process flowsheets have been developed which combine chloride leaching of copper from chalcopyrite with solvent extraction, to selectively transfer copper to a conventional sulfate electrowinning circuit. Chloride leaching with copper(II) as oxidant offers significant advantages for copper including increased solubility and increased rates of leaching. Both process flowsheets were similarly designed with a two stage counter-current leach but differ with respect to iron deportment. The goethite model flowsheet includes sparging of air or oxygen to the second leach stage to aid precipitation of iron as goethite (FeOOH). The hematite model flowsheet precipitates iron as hematite (Fe2O3) downstream from the leach in a dedicated autoclave. A mass balance has been completed for both process flowsheets and this determined the concentrations of copper and iron species in feed liquor returning to the leach following copper solvent extraction. The optimum leach extraction conditions were determined by varying grind size, temperature and residence time for both leach model scenarios. Leach tests were conducted using a chalcopyrite concentrate from Antamina in northern Peru, which contains a low to moderate amount of gangue material. The hematite model was also examined using a Rosario concentrate from Chile which contained chalcocite in addition to chalcopyrite and significant pyrite. Leach tests based on the hematite model were successful in achieving copper extractions N95% in 4–6 h at 95 °C after fine grinding the concentrate (P90 = 41 μm). However, copper extraction exceeded 99% from the finely ground Rosario concentrate (P90 = 37 μm). In the goethite model leach tests, 89% copper extraction was achieved under optimum conditions in the atmospheric conditions tested. © 2007 Elsevier B.V. All rights reserved. Keywords: Chloride leaching; Chalcopyrite concentrate; Goethite; Hematite; Copper process
1. Introduction Currently, commercial hydrometallurgical processes for copper largely feature sulfate-based heap or pressure leaching combined with solvent extraction and recovery via electrowinning, and are generally suitable for processing copper oxides or secondary copper sulfides such as covellite or chalcocite. Chalcopyrite is difficult to leach and competing sulfate based pressure oxygen ⁎ Corresponding author. Tel.: +1 604 822 4805. E-mail address: [email protected] (D. Dreisinger). 0304-386X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.hydromet.2007.08.004
leach systems are investigating fine grinding and addition of surfactants to overcome passivation effects of molten sulfur and product layer diffusion obstruction (Hackl et al., 1995; Dreisinger et al., 2003). Chloride leaching, however, has been extensively proven to extract N95% of copper from CuFeS2 at temperatures around the boiling point and at atmospheric pressure (Winand, 1991; Dutrizac, 1992; Flett, 2002). Chloride leaching offers significant advantages for hydrometallurgical processing, in supporting high metal solubility, enhanced redox behaviour, and increased rates of leaching. In this system, both cuprous ion and
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Fig. 1. The Hematite Process.
cupric ion, as well as several other metal ions are stabilized through complexation with chloride ion (Winand, 1991); and thus has potential for treating complex ores and concentrates. Yet despite the effectiveness of chloride leaching, progression toward commercial activity has been slow due to problems with product purity and morphology and technological challenges in handling corrosive process liquors (Hoffman, 1991; Dutrizac, 1992). Various strategies of copper recovery from chloride leaching that have been attempted over the last 30 years at the laboratory, pilot and demonstration scale include recovery as CuCl; direct electrowinning from copper (I) leach liquors; solvent extraction and electrowinning from copper(II) chloride; and solvent extraction and electrowinning from copper(II) sulfate (Dalton et al., 1991; Peters, 1976; Moyes et al., 2000; Satchell and Gerlach, 1986; Winand, 1991). Only the Duval Corporation's CLEAR process has operated commercially, for a period of six years, until it was closed due to various technical and economic reasons. In particular, the product still required further refining to achieve wirebar- or cathode-grade material (Hoffman, 1991; Dutrizac, 1992; Schweitzer and Livingstone, 1982). In this work, two new process flowsheets, shown in Figs. 1 and 2, were developed featuring chloride leaching of chalcopyrite combined with solvent extraction and conventional sulfate electrowinning to address the issue of recovering a pure product. They differ, however, with respect to iron deportment. The Hematite Process, in which no air is introduced to the leach, allows separate sulfur and iron residues to be produced, thus making waste treatment and disposal potentially easier. The Goethite Process offers simplicity in overall flowsheet design, and air/oxygen is sparged to the leach to precipitate iron as goethite (FeOOH) for disposal with the leach residue. The solvent extraction step can be performed using a conventional oxime extractant after oxidation of cuprous
to cupric using oxygen at the extraction stage. A wash stage is important to prevent chloride ions transferring to the sulfate electrowinning circuit where there is potential for corrosion of the stainless steel cathodes. This technique has not been demonstrated at commercial scale, but has been demonstrated in bench scale work (Demarthe et al., 1976; Demarthe and Georgeaux, 1978). This paper presents mass balance information important in the development of both process flowsheets. This paper also includes the results of countercurrent leach experiments to determine optimum leaching conditions for both leach model scenarios. The mass balance provided concentrations and species of copper and iron required in the feed liquor for the leach experiments. The leach conditions chosen for the 2 stage countercurrent leach experiments were based on literature investigations that indicated an atmospheric leach, near boiling point, at low pH, using relatively fine particles and high concentrations of chloride and copper (II) oxidant are important for effective and efficient leaching of chalcopyrite (Bonan et al., 1981; Dutrizac, 1981; Wilson and Fisher, 1981). As the reaction rate is linear with temperature and the rate determined to be surface reaction controlled, particle size, temperature and leach time were varied in the experiments to achieve higher extractions of copper. A novel ‘mini-thickener’ apparatus was developed and used to aid smoother S–L separation and transfer on a laboratory scale. 2. Experimental methods 2.1. Feed concentrates The copper concentrates tested originated from Antamina in northern Peru and from the Rosario deposit at Collahuasi in Chile. The concentrates were analysed by Inductively Coupled Plasma (ICP) spectrometry and for total sulfur. Particle size was
Fig. 2. The Goethite Process.
J. Liddicoat, D. Dreisinger / Hydrometallurgy 89 (2007) 323–331 Table 1 Feed concentrate analysis and particle size Feed concentrate
Cu %
Fe %
S%
Particle size
Antamina FG Antamina FG Rosario
28.8 28.5 26.8
28.4 28.7 26.8
32.1 32.4 35.5
P90 = 75 μm P50 = 16 μm, P90 = 41 μm P50 = 16 μm, P90 = 37 μm
FG = finely ground.
analysed by wet sieving the coarser material, and by a Malvern Mastersizer laser analyzer for finely ground material. The assay values and particle size analysis are shown in Table 1. X-ray diffraction spectrometry (XRD) was used to characterize both concentrates. The Antamina concentrate consisted largely of chalcopyrite with a low-moderate amount of pyrite, silica, sphalerite, zinc oxide and molybdenite. The Rosario concentrate consisted of chalcopyrite and chalcocite with a significant amount of pyrite and lesser amounts of silica, molybdenite, and sphalerite. 2.2. Feed solutions Feed liquor concentrations were based on the mass balances for each process flowsheet. Feed solutions were prepared in deionised water using technical grade FeCl3; CaCl2 pellets; and laboratory grade CuCl2·2H2O and HCl (25%w/v). Powdered iron was used to reduce ferric ions to ferrous ions in the leach feed liquor for experiments based on the goethite model. A background concentration of free HCl was targeted at approximately 3 g/L. Total chloride concentration was greater than 5 M with contributions from CuCl2·2H2O, FeCl3 and CaCl2. Samples of the feed solution were diluted as required for analysis of HCl (by oxalate masking NaOH titration), ferrous ions by cerium titration, metals ions by ICP, ferric ions as the difference between total iron and ferrous ions, and total chloride, using an ion selective electrode (ISE).
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As determined from the mass balance, feed liquor concentrations to leach stage two for the goethite model experiments required 50 g/L Cu2+ and 30 g/L Fe2+ whilst the hematite model experiments required 50 g/L Cu2+ and 80 g/L Fe3+. 2.3. Experimental apparatus A schematic of the two-stage countercurrent leach circuit is shown in Fig. 3. For solid–liquid (S–L) separation one minithickener (Th1), was incorporated between Leach Stage 1 (LS1) and Leach Stage 2 (LS2) and pressure filtration (P.F.) was used to separate final leach residues. The filtrate from pressure filtration (LS2 liquor) was then transferred counter-currently to LS1. Leach experiments were conducted using 2 L glass waterjacketed vessels, containing 1 L volume and were sealed with a high-density polyethylene (HDPE) lid with ports for thermocouple, pH and Eh probes, titanium stirrer shaft and condenser. Peristaltic pumps were used to transfer the leach slurry through Masterflex tubing. For experiments based on the goethite model, air or oxygen was sparged inside the Leach Stage 2 vessel via a long polycarbonate tube (9.5 mm in diameter). The glass mini-thickener design used for bench-scale solidliquid separation is shown in Fig. 4. A slow moving internal titanium rake was used to aid movement of solids through the bottom exit. Flocculant was used to aid settling of solids. The mini-thickener overflow ports were not used in this work. Instead, the supernatant was pumped to enable counter-current liquor transfer. 2.4. Sampling and analysis LS1 and LS2 slurry samples (∼ 80 mL) were collected at the end of each leach stage. All liquor samples, chloride wash water and washed leach residue samples were analysed for metals by ICP and selected liquor samples were analysed for free acid and for total chloride. Total reduced species (Cu+ and Fe2+ ions) were determined by cerium titration. The
Fig. 3. Experimental Set-up.
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a better indication of acid concentration. Redox potential, Eh, measurements were largely performed using a Pt/Ag/AgCl (4 M KCl) combination electrode. Redox potential measurements taken in the leach vessels were not corrected for temperature and largely serve a comparative purpose between experiments.
3. Excel mass balance outputs for hematite and goethite process flowsheets Mass balances for both flowsheets were completed in Excel in which 135 g pure CuFeS2 concentrate was introduced to the circuit and it was assumed that 100% of the copper and iron in CuFeS2 was leached. Subsequently all of the copper extracted was removed via SX and all iron extracted was precipitated, either as goethite or hematite. The models were simplified to include only major reactions, assumed from previous experimental work and literature (Peters, 1977; Winand, 1991; Dutrizac, 1992; Fisher, 2001). For each stream, the copper and iron species are written as simple cations but are assumed to be associated with chloride. A background concentration of 110 g/L CaCl2 was used to ensure a concentrated chloride medium N5 M. HCl was also included in both models, and remains constant as a result of acid consuming and generating reactions. In these simplified models, gypsum precipitation is not considered, as minimal sulfate production is expected (Winand, 1991; Szymanowski, 1996). 3.1. The hematite process Fig. 4. Mini-thickener design.
feed concentrate and final LS2 residue samples were also analysed for sulfur speciation. From the mass balance, the predicted exit PLS concentrations from Leach Stage 1 in the goethite model experiments are 94 g/L Cu+, 1.9 g/L Cu2+ and 31 g/L Fe2+ ions. For the hematite model experiments the exit PLS concentrations from Leach Stage 1 are 96 g/L Cu+, 1.5 g/L Cu2+ and 121 g/L Fe2+ ions. The PLS analysis measured in this work was as expected in proportion to the extraction of Cu and Fe achieved. Although the reduced species in the PLS were 10% lower than predicted, due to the air oxidation of cuprous ion, the impact for either flowsheet is not problematic. 2.5. pH and redox measurement pH measurements were only taken at room temperature in the filtered samples using a refillable combination electrode with a ceramic junction. The pH measurements have not been corrected for liquid junction potential, and were generally near pH 0 or lower. Hence, free acid titrations in the feed and final PLS provide
This model focuses on 3 major process units (see Fig. 1), a 2 stage counter-current leach, copper solvent extraction and iron precipitation in an autoclave. The input and output streams for LS1, LS2, SX and Table 2 Hematite process streams Stream From autoclave to Leach Stage 2 From Leach Stage 2 to Leach Stage 1 From Leach Stage 1 to solvent extraction From solvent extraction to autoclave
Cu+ (g)
Cu2+ (g)
Fe2+ (g)
Fe3+ (g)
0
50.3
0
80.2
0
73.0
99.6
0.5
95.5
1.5
121.3
0
2.0
48.3
121.3
0
Feed, 100% CuFeS2 (135 g), Extent of CuFeS2 leaching: LS1 = 51.5%; LS2 = 48.5%. Solution contains 110 g CaCl2; 2 g HCl; 1000 g H2O.
J. Liddicoat, D. Dreisinger / Hydrometallurgy 89 (2007) 323–331 Table 3 Goethite process streams Stream From solvent extraction to Leach Stage 2 From Leach Stage 2 to leach stage 1 From Leach Stage 1 to solvent extraction
Cu+ (g)
Cu2+ (g)
Fe2+ (g)
Fe3+ (g)
0
48.7
31.1
0
0
69.7
0.3
93.5
1.9
31.1
8.2 0
Feed, 100% CuFeS2 (135 g), Extent of CuFeS2 leaching: LS1 = 55%; LS2 = 45%. Solution contains 110 g CaCl2; 2 g HCl; 1000 g H2O.
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with the hematite model, the input and output stream data is shown in Table 3 and assumed reactions are shown by Eqs. (8)–(15). Stage 2 (LS2) CuFeS2 þ 3CuCl2 →4CuCl þ FeCl2 þ 2So
ð8Þ
2CuCl þ 0:5O2 þ 2HCl→2CuCl2 þ H2 O
ð9Þ
2FeCl2 þ 0:5O2 þ 2HCl→2FeCl3 þ H2 O
ð10Þ
2FeCl3 þ 4H2 O→2FeOOHðsÞ þ 6HCl
ð11Þ
autoclave determined from the mass balance for this flowsheet are shown in Table 2; and the assumed reactions for each unit operation are included as Equations (1)–(7) shown below. In reaction 4, only half the copper is extracted due to balancing the acid generated with the acid required for the oxidation of cuprous to cupric. Note also that not all iron is precipitated in the autoclave, as ferric ions return to Leach Stage 2 as an oxidant for leaching. Leach Stage 2 (LS2)
ð10 and 11Þ2FeCl2 þ 0:5O2 þ 3H2 O→2FeOOHðsÞ þ4HCl ð12Þ
CuFeS2 þ 4FeCl3 →5FeCl2 þ CuCl2 þ 2So
2CuCl þ 0:5O2 þ 2HRorg →CuR2org þ CuCl2 þ H2 O
ð1Þ
Leach Stage 1 (LS1) CuFeS2 þ 4FeCl3 →5FeCl2 þ CuCl2 þ 2So
ð13Þ
CuFeS2 þ 3CuCl2 →4CuCl þ FeCl2 þ 2So
ð14Þ
Solvent extraction (SX)
ð15Þ
Leach Stage 1 (LS1) CuFeS2 þ 4FeCl3 →5FeCl2 þ CuCl2 þ 2So
ð2Þ
CuFeS2 þ 3CuCl2 →4CuCl þ FeCl2 þ 2So
ð3Þ
Solvent extraction (SX) 2CuCl þ 0:5O2 þ 2HRorg →CuR2org þ CuCl2 þ H2 O ð4Þ Hematite precipitation in autoclave (A/C) 2FeCl2 þ 0:5O2 þ 2H2 O→Fe2 O3ðsÞ þ 4HCl
ð5Þ
2CuCl þ 0:5O2 þ 2HCl→2CuCl2 þ H2 O
ð6Þ
2FeCl2 þ 0:5O2 þ 2HCl→2FeCl3 þ H2 O
ð7Þ
3.2. The Goethite process This process focuses only on 2 major process units (see Fig. 2), and despite being simpler in overall flowsheet design than the hematite model, the leach is more complex as oxygen or air is added to precipitate goethite in LS2 thus producing a mixed sulfur/iron residue. As
3.3. Testwork matrix for the counter-current leach experiments Twelve continuous counter-current leach experiments were performed. The order, model basis and conditions used are shown in Table 4. The experimental identifier indicates upon which process model the leach Table 4 Order of experiments Expt.
Feed concentrate
RT (h)
Total time (h)
Temp. (°C)
Air/O2 to LS2 (flow rate)
H1 H2 H3 H4 H5
Antamina
2 2 3 3 3
10.75 10 18 18 18
85 95 85 95 95
No No No No No
2 3 2 2 2 3
12 18 12 10 10 18
95 85 85 85 95 95
No No No Air (200 mL/min) Air (2.5 L/min) O2 (2.5 L/min)
3
17.5
95
No
H6 H7 H8 G1 G2 G3 H9
↓
FG Antamina
↓
Antamina
↓
FG Antamina FG Rosario
RT = residence time per leach stage.
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Table 5 Feed solutions for hematite model experiments Experiment Feed solution to leach stage 2
H1 H2 H3 H4 H5 H6 H7 H8
Cl− [M]
E mV Ag/ pHa AgCla
7.2 7.4 7.2 8.0 6.3 6.4 8.0 7.2
648 650 639 661 677 660 659 661
− 0.48 − 0.24 − 0.36 − 0.35 − 0.16 − 0.25 − 0.68 − 0.67
Cu2+ g/L
Fe3+ g/L
Free acid (as HCl) g/L
47.8 47.2 52.9 55.8 45.0 41.1 47.7 48.0
76.7 79.9 87.2 90.6 76.0 70.2 80.1 75.3
5.7 5.3 4.0 4.0 2.7 1.9 3.0 3.7
a
Measured at room temperature.
was based, ‘H’ representing the hematite process and ‘G’ the goethite process. The residence time (RT) quoted in the table is per each leach stage, and the total time for each experiment was for 2–3 total (2 stage) leach cycles. The aim of these experiments was to find conditions to achieve maximum copper extraction (N95%) with both models by varying conditions of residence time, temperature and particle size. The first eleven experiments were conducted using Antamina concentrate and the final experiment was performed using finely ground Rosario concentrate, at the optimum conditions determined from the previous experiments. Analyses of feed liquor introduced to Leach Stage 2 are reported in Tables 5, 7 and 9. Copper and iron extraction was determined by the difference between the analysis of the feed solids and the final bulk solid residues leaving Leach Stage 2. 4. Results and discussion 4.1. Results of hematite model experiments
Fig. 5. Cu and Fe (%) Extraction over several leach cycles for Experiment H5 [P80 = 41 μm, 3 h per leach stage at 95 °C].
time and temperature. The first four experiments employed “as received” Antamina concentrate (P90 = 75 μm), whilst the successive four experiments employed finely ground concentrate (P90 = 41 μm). These experiments revealed that increasing the temperature from 85 °C to 95 °C had a greater impact on extraction than increasing the residence time from 2 h to 3 h. For the first four experiments, the highest copper extraction achieved was 93%, employing a 3 h leach stage residence time at 95 °C. As N 95% copper extraction in chloride media has been well demonstrated by others (Winand, 1991; Dutrizac, 1992), the subsequent experiments H5-H8 were performed on the finer material in order to achieve higher copper extraction. Here, the highest copper extraction was 98%, employing a 3 h leach stage residence time at 95 °C (H5), and plots of Cu and Fe % extractions and Cu and Fe the final leach residue can be seen over several leach cycles in Figs. 5 and 6. Experiments H6 and H7 with
The results of eight experiments based on the hematite leach model are shown in Table 6 with varying residence Table 6 Results for Hematite model experiments Experiment
H1 H2 H3 H4 H5 H6 H7 H8
Exit PLS solution from LS1
Final LS2 residue
CuTotal g/L
FeTotal g/L
Cu% extn
Fe% extn
74.1 81.8 86.3 94.6 86.0 75.3 81.1 80.4
101.7 114.3 125.1 127.9 118.0 103.9 112.9 106.5
80 87 83 93 98 96 96 90
74 80 76 85 91 88 89 83
Fig. 6. Cu and Fe in LS2 Residue over several leach cycles from Experiment H5 [P80 = 41 μm, 3 h per leach stage at 95 °C].
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Table 7 Feed solutions for Goethite model experiments Experiment Feed Solution to Leach Stage 2 Cl- E pH [M] mV Ag/ Ag/ Cl a G1 G2 G3
4.5 5.7 5.6
Cu2+ Fe3+ Fe2+ CaCl2 Free Acid g/L g/L g/L g/L (as HCl) g/L
463 0.02 54.1 7.9 27.1 110 457 − 0.47 55.9 11.6 22.9 220 443 − 0.29 47.4 4.9 25.1 220
0.7 10.0 b0.01
Due to the high air/oxygen flow rate (in G2 and G3) the temperature of the leach was depressed by approximately 4 °C from the starting water bath temperature down to 91 °C. a Measured at room temperature.
shorter residence time or lower temperature, both reported copper extractions of 96%. The % extraction Cu and Fe, and the Cu and Fe remaining in the final residue remained constant +/− 1% over several leach cycles after the first cycle. The lower values reported for iron extraction in Table 6 (74%– 91%) were found to represent iron remaining as undisturbed pyrite (FeS2) in addition to iron remaining from unleached chalcopyrite (CuFeS2). 4.2. Results of Goethite model experiments Three experiments based on the goethite leach model were performed, and the feed conditions and extraction results are shown in Tables 7 and 8. In the first two experiments air was added to Leach Stage 2 to regenerate cupric ions for further leaching and ferric ions for goethite precipitation. However, both of these experiments were not successful in achieving high copper extractions, indicating insufficient re-oxidation of Fe3+ or Cu2+ ions. For the third experiment, G3, finely ground concentrate and 98% oxygen were used to achieve higher copper extraction of 89% with a 3 h residence time at 95 °C. Following the first three cycles in experiment G3, copper extraction stabilized at 89% (see Fig. 7) and a much higher oxidation potential was recorded in Leach Stage 2. A high oxygen gas flow rate Table 8 Results for Goethite model experiments Experiment
G1 G2 G3
Fig. 7. Cu and Fe (%) Extraction over several leach cycles for Experiment G3 [P80 = 37 μm, 3 h per leach stage at 95 °C].
overcomes oxygen solubility inefficiency limitations at the bench scale. However, an industrial scale reactor can be designed to increase oxygen utilization efficiency using air. It was also intended that the feed liquor contain a low concentration (b 3 g/L) of free acid (as HCl) to promote goethite precipitation. Experiment G2 however had 10.0 g/L HCl resulting in inefficient iron precipitation and no better copper extraction. Though the goethite leach experiments were not successful in achieving N 95% copper extraction there is potential for doing so with further work. 4.3. Application of hematite leach model to Rosario concentrate A final experiment was conducted based on the Hematite Process leach model using finely ground Rosario concentrate (P90 = 37 μm) with a leach stage residence time of 3 h at 95 °C. The Rosario concentrate contains a similar amount of copper (26.8%) as the Antamina concentrate (28.5%), but less chalcopyrite and more chalcocite. Experimental feed conditions and extraction results are shown in Table 9. Surprisingly, not only was the final copper extraction 98%, but by the end of the first Table 9 Feed conditions and extraction results for the H9 Rosario experiment
Exit PLS Solution from LS1
Final LS2 Residue
CuTotal g/L
FeTotal g/L
Cu% Extn
Fe% extn
55.5 87.9 93.9
27.6 59.7 26.2
60 67 89
13 53 −7
Expt. Stream Solution
Solids
Percentage extn
Cu g/L Fe g/L Mass g Cu % Fe % Cu % Fe % H9
Feed LS1 LS2
50.6 91.7 55.1
82.0 100.5 84.9
135 76.3 68.6
26.8 2.1 1.1
26.8 28.3 27.5
96 98
40 48
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Table 10 Trace metal analysis Element
Ag Cr Pb Mg Ni Zn
Extraction % based on final LS2 residue H5
G3
H9 (Rosario)
97.1 92.1 99.9 96.7 93.0 98.9
92.4 46.2 99.7 93.4 90.1 98.4
98.9 93.9 94.3 95.5 92.4 98.7
background salt may be possible for the hematite model as there is no iron precipitation in the leach, and hence there is no concern for jarosite formation. The goethite model experiments only achieved 89% copper extraction under comparable optimum conditions. However, longer residence times or finer grinding to 20 microns or the use of an autoclave for Leach Stage 2 may increase copper extraction, as is required for some competing sulfate based leach processes. Acknowledgements
leach stage 96% extraction had already been achieved. The presence of less refractory Cu2S along with pyrite in the concentrate contribute to the significantly decreased leaching time (Eqs. (16) and (17)). Cu2 S þ 2FeCl3 →2FeCl2 þ 2CuCl þ So
ð16Þ
Cu2 S þ 2CuCl2 →4CuCl þ So
ð17Þ
4.4. Trace metals All the elements reported in ICP analysis were examined to determine which other elements were leached with copper. Table 10 reports the extraction values of these elements in the final LS2 residues of three experiments. Silver (Ag), lead (Pb), nickel (Ni) and zinc (Zn) all reported significantly high extractions above 90%. This indicates the high suitability of chloride leaching for most complex sulfides. 5. Conclusions Two new process flowsheets have been developed, the Goethite Process and the Hematite Process, which combine Cu(II)/chloride leaching for copper with solvent extraction, to selectively transfer copper to a conventional sulfate electrowinning circuit. Solvent extraction (SX) is a known and effective method for selective uptake of copper for transfer to an electrowinning circuit with minimal impurity carry-over. However, the carry-over of chloride ion needs further investigation. With respect to iron deportment the flowsheets offer flexibility. As goethite (FeOOH) is a less stable iron residue in the environment than hematite (Fe2O3) it is important to have two process options because in some localities goethite will not be accepted in waste for disposal. The counter-current leach experiments performed for the hematite model achieved N95% copper extractions using a relatively straight forward 2-stage leach and the separation of sulfur leach residue from iron precipitate. The substitution of NaCl for CaCl2 as
The authors would like to thank Falconbridge Limited for funding this study. The technical assistance of Dr. Mohamed Buarzaiga of Falconbridge, UBC colleagues and the assistance of Prabhjit Bhatia in conducting the pilot work are gratefully acknowledged. References Bonan, M., Demarthe, J.M., Renon, H., Baratin, F., 1981. Chalcopyrite leaching by CuCl2 in strong NaCl solutions. Metall. Trans. 12B, 269–274. Dalton, R.F., Diaz, G., Price, R., Zunkel, A.D., 1991. The CUPREX metal extraction process: recovering copper from sulfide ores. JOM August, pp. 51–56. Demarthe, J.M., Georgeaux, A., 1978. Hydrometallurgical treatment of complex suphides. Complex Metallurgy '78. I.M.M, London, pp. 113–120. Demarthe, J.M., Gandon, L., Georgeaux, A., 1976. A new hydrometallurgical process for copper. In: Yannopoulos, J.C., Agarwal, J.C. (Eds.), Extractive Metallurgy of Copper. TMS-AIME, New York, pp. 825–848. Dreisinger, D.B., Marsh, J., Dempsey, P., 2003. The Anglo-American Corporation/University of British Columbia (AAC/UBC) chalcopyrite copper hydrometallurgy process. Cobre 2003, 5th Intl. Conference, Santiago, Chile. Metallurgical Society, Montreal, Canada, pp. 223–238. Dutrizac, J.E., 1981. The dissolution of chalcopyrite in ferric sulfate and ferric chloride media. Metall. Trans. 12B, 371–378. Dutrizac, J.E., 1992. The leaching of sulphide minerals in chloride media. Hydrometallurgy 29, 1–45. Fisher, N., 2001. Countercurrent leaching of chalcopyrite in cupric/ ferric chloride media. Falconbridge Copper Chloride Leaching Project Report. University of British Columbia, Vancouver. Flett, D.S., 2002. Chloride hydrometallurgy for complex sulphides: a review. CIM Bull. 95 (1065), 95–103. Hackl, R.P., Dreisinger, D.B., Peters, E., King, J.A., 1995. Passivation of chalcopyrite during oxidative leaching in sulfate media. Hydrometallurgy 39, 25–48. Hoffman, J.E., 1991. Winning copper via chloride chemistry — an elusive technology. JOM August, pp. 48–49. 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. Peters, E., 1976. Direct leaching of sulfides: chemistry and applications. Metall. Trans. 7B, 505–517.
J. Liddicoat, D. Dreisinger / Hydrometallurgy 89 (2007) 323–331 Peters, E., 1977. Applications of chloride hydrometallurgy to treatment of sulphide minerals. Proceedings of Chloride Hydrometallurgy, Brussels, Benelux Metallurgie, pp. 1–37. Satchell, D.P., Gerlach, J.N., 1986. Chloride hydrometallurgical process for production of copper. US Patent 4,594,132. Schweitzer, F.W., Livingstone, R.W., 1982. Duval's CLEAR hydrometallurgical process. In: Parker, P.D. (Ed.), Chloride Electrometallurgy. TMS-AIME, New York, pp. 221–227.
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Szymanowski, J., 1996. Copper hydrometallurgy and extraction from chloride media. J. Radioanal. Nucl. Chem. Artic. 208 (1), 183–194. Wilson, J.P., Fisher, W.W., 1981. Cupric chloride leaching of chalcopyrite. JOM February, pp. 52–57. Winand, R., 1991. Chloride hydrometallurgy. Hydrometallurgy 27, 285–316.
Hydrometallurgy 89 (2007) 323 – 331 www.elsevier.com/locate/hydromet
Chloride leaching of chalcopyrite J. Liddicoat, D. Dreisinger ⁎ University of British Columbia, Department Metals and Materials Engineering, Vancouver, BC, Canada V6T 1Z4 Received 20 October 2006; received in revised form 7 August 2007; accepted 9 August 2007 Available online 17 August 2007
Abstract Two new process flowsheets have been developed which combine chloride leaching of copper from chalcopyrite with solvent extraction, to selectively transfer copper to a conventional sulfate electrowinning circuit. Chloride leaching with copper(II) as oxidant offers significant advantages for copper including increased solubility and increased rates of leaching. Both process flowsheets were similarly designed with a two stage counter-current leach but differ with respect to iron deportment. The goethite model flowsheet includes sparging of air or oxygen to the second leach stage to aid precipitation of iron as goethite (FeOOH). The hematite model flowsheet precipitates iron as hematite (Fe2O3) downstream from the leach in a dedicated autoclave. A mass balance has been completed for both process flowsheets and this determined the concentrations of copper and iron species in feed liquor returning to the leach following copper solvent extraction. The optimum leach extraction conditions were determined by varying grind size, temperature and residence time for both leach model scenarios. Leach tests were conducted using a chalcopyrite concentrate from Antamina in northern Peru, which contains a low to moderate amount of gangue material. The hematite model was also examined using a Rosario concentrate from Chile which contained chalcocite in addition to chalcopyrite and significant pyrite. Leach tests based on the hematite model were successful in achieving copper extractions N95% in 4–6 h at 95 °C after fine grinding the concentrate (P90 = 41 μm). However, copper extraction exceeded 99% from the finely ground Rosario concentrate (P90 = 37 μm). In the goethite model leach tests, 89% copper extraction was achieved under optimum conditions in the atmospheric conditions tested. © 2007 Elsevier B.V. All rights reserved. Keywords: Chloride leaching; Chalcopyrite concentrate; Goethite; Hematite; Copper process
1. Introduction Currently, commercial hydrometallurgical processes for copper largely feature sulfate-based heap or pressure leaching combined with solvent extraction and recovery via electrowinning, and are generally suitable for processing copper oxides or secondary copper sulfides such as covellite or chalcocite. Chalcopyrite is difficult to leach and competing sulfate based pressure oxygen ⁎ Corresponding author. Tel.: +1 604 822 4805. E-mail address: [email protected] (D. Dreisinger). 0304-386X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.hydromet.2007.08.004
leach systems are investigating fine grinding and addition of surfactants to overcome passivation effects of molten sulfur and product layer diffusion obstruction (Hackl et al., 1995; Dreisinger et al., 2003). Chloride leaching, however, has been extensively proven to extract N95% of copper from CuFeS2 at temperatures around the boiling point and at atmospheric pressure (Winand, 1991; Dutrizac, 1992; Flett, 2002). Chloride leaching offers significant advantages for hydrometallurgical processing, in supporting high metal solubility, enhanced redox behaviour, and increased rates of leaching. In this system, both cuprous ion and
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Fig. 1. The Hematite Process.
cupric ion, as well as several other metal ions are stabilized through complexation with chloride ion (Winand, 1991); and thus has potential for treating complex ores and concentrates. Yet despite the effectiveness of chloride leaching, progression toward commercial activity has been slow due to problems with product purity and morphology and technological challenges in handling corrosive process liquors (Hoffman, 1991; Dutrizac, 1992). Various strategies of copper recovery from chloride leaching that have been attempted over the last 30 years at the laboratory, pilot and demonstration scale include recovery as CuCl; direct electrowinning from copper (I) leach liquors; solvent extraction and electrowinning from copper(II) chloride; and solvent extraction and electrowinning from copper(II) sulfate (Dalton et al., 1991; Peters, 1976; Moyes et al., 2000; Satchell and Gerlach, 1986; Winand, 1991). Only the Duval Corporation's CLEAR process has operated commercially, for a period of six years, until it was closed due to various technical and economic reasons. In particular, the product still required further refining to achieve wirebar- or cathode-grade material (Hoffman, 1991; Dutrizac, 1992; Schweitzer and Livingstone, 1982). In this work, two new process flowsheets, shown in Figs. 1 and 2, were developed featuring chloride leaching of chalcopyrite combined with solvent extraction and conventional sulfate electrowinning to address the issue of recovering a pure product. They differ, however, with respect to iron deportment. The Hematite Process, in which no air is introduced to the leach, allows separate sulfur and iron residues to be produced, thus making waste treatment and disposal potentially easier. The Goethite Process offers simplicity in overall flowsheet design, and air/oxygen is sparged to the leach to precipitate iron as goethite (FeOOH) for disposal with the leach residue. The solvent extraction step can be performed using a conventional oxime extractant after oxidation of cuprous
to cupric using oxygen at the extraction stage. A wash stage is important to prevent chloride ions transferring to the sulfate electrowinning circuit where there is potential for corrosion of the stainless steel cathodes. This technique has not been demonstrated at commercial scale, but has been demonstrated in bench scale work (Demarthe et al., 1976; Demarthe and Georgeaux, 1978). This paper presents mass balance information important in the development of both process flowsheets. This paper also includes the results of countercurrent leach experiments to determine optimum leaching conditions for both leach model scenarios. The mass balance provided concentrations and species of copper and iron required in the feed liquor for the leach experiments. The leach conditions chosen for the 2 stage countercurrent leach experiments were based on literature investigations that indicated an atmospheric leach, near boiling point, at low pH, using relatively fine particles and high concentrations of chloride and copper (II) oxidant are important for effective and efficient leaching of chalcopyrite (Bonan et al., 1981; Dutrizac, 1981; Wilson and Fisher, 1981). As the reaction rate is linear with temperature and the rate determined to be surface reaction controlled, particle size, temperature and leach time were varied in the experiments to achieve higher extractions of copper. A novel ‘mini-thickener’ apparatus was developed and used to aid smoother S–L separation and transfer on a laboratory scale. 2. Experimental methods 2.1. Feed concentrates The copper concentrates tested originated from Antamina in northern Peru and from the Rosario deposit at Collahuasi in Chile. The concentrates were analysed by Inductively Coupled Plasma (ICP) spectrometry and for total sulfur. Particle size was
Fig. 2. The Goethite Process.
J. Liddicoat, D. Dreisinger / Hydrometallurgy 89 (2007) 323–331 Table 1 Feed concentrate analysis and particle size Feed concentrate
Cu %
Fe %
S%
Particle size
Antamina FG Antamina FG Rosario
28.8 28.5 26.8
28.4 28.7 26.8
32.1 32.4 35.5
P90 = 75 μm P50 = 16 μm, P90 = 41 μm P50 = 16 μm, P90 = 37 μm
FG = finely ground.
analysed by wet sieving the coarser material, and by a Malvern Mastersizer laser analyzer for finely ground material. The assay values and particle size analysis are shown in Table 1. X-ray diffraction spectrometry (XRD) was used to characterize both concentrates. The Antamina concentrate consisted largely of chalcopyrite with a low-moderate amount of pyrite, silica, sphalerite, zinc oxide and molybdenite. The Rosario concentrate consisted of chalcopyrite and chalcocite with a significant amount of pyrite and lesser amounts of silica, molybdenite, and sphalerite. 2.2. Feed solutions Feed liquor concentrations were based on the mass balances for each process flowsheet. Feed solutions were prepared in deionised water using technical grade FeCl3; CaCl2 pellets; and laboratory grade CuCl2·2H2O and HCl (25%w/v). Powdered iron was used to reduce ferric ions to ferrous ions in the leach feed liquor for experiments based on the goethite model. A background concentration of free HCl was targeted at approximately 3 g/L. Total chloride concentration was greater than 5 M with contributions from CuCl2·2H2O, FeCl3 and CaCl2. Samples of the feed solution were diluted as required for analysis of HCl (by oxalate masking NaOH titration), ferrous ions by cerium titration, metals ions by ICP, ferric ions as the difference between total iron and ferrous ions, and total chloride, using an ion selective electrode (ISE).
325
As determined from the mass balance, feed liquor concentrations to leach stage two for the goethite model experiments required 50 g/L Cu2+ and 30 g/L Fe2+ whilst the hematite model experiments required 50 g/L Cu2+ and 80 g/L Fe3+. 2.3. Experimental apparatus A schematic of the two-stage countercurrent leach circuit is shown in Fig. 3. For solid–liquid (S–L) separation one minithickener (Th1), was incorporated between Leach Stage 1 (LS1) and Leach Stage 2 (LS2) and pressure filtration (P.F.) was used to separate final leach residues. The filtrate from pressure filtration (LS2 liquor) was then transferred counter-currently to LS1. Leach experiments were conducted using 2 L glass waterjacketed vessels, containing 1 L volume and were sealed with a high-density polyethylene (HDPE) lid with ports for thermocouple, pH and Eh probes, titanium stirrer shaft and condenser. Peristaltic pumps were used to transfer the leach slurry through Masterflex tubing. For experiments based on the goethite model, air or oxygen was sparged inside the Leach Stage 2 vessel via a long polycarbonate tube (9.5 mm in diameter). The glass mini-thickener design used for bench-scale solidliquid separation is shown in Fig. 4. A slow moving internal titanium rake was used to aid movement of solids through the bottom exit. Flocculant was used to aid settling of solids. The mini-thickener overflow ports were not used in this work. Instead, the supernatant was pumped to enable counter-current liquor transfer. 2.4. Sampling and analysis LS1 and LS2 slurry samples (∼ 80 mL) were collected at the end of each leach stage. All liquor samples, chloride wash water and washed leach residue samples were analysed for metals by ICP and selected liquor samples were analysed for free acid and for total chloride. Total reduced species (Cu+ and Fe2+ ions) were determined by cerium titration. The
Fig. 3. Experimental Set-up.
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a better indication of acid concentration. Redox potential, Eh, measurements were largely performed using a Pt/Ag/AgCl (4 M KCl) combination electrode. Redox potential measurements taken in the leach vessels were not corrected for temperature and largely serve a comparative purpose between experiments.
3. Excel mass balance outputs for hematite and goethite process flowsheets Mass balances for both flowsheets were completed in Excel in which 135 g pure CuFeS2 concentrate was introduced to the circuit and it was assumed that 100% of the copper and iron in CuFeS2 was leached. Subsequently all of the copper extracted was removed via SX and all iron extracted was precipitated, either as goethite or hematite. The models were simplified to include only major reactions, assumed from previous experimental work and literature (Peters, 1977; Winand, 1991; Dutrizac, 1992; Fisher, 2001). For each stream, the copper and iron species are written as simple cations but are assumed to be associated with chloride. A background concentration of 110 g/L CaCl2 was used to ensure a concentrated chloride medium N5 M. HCl was also included in both models, and remains constant as a result of acid consuming and generating reactions. In these simplified models, gypsum precipitation is not considered, as minimal sulfate production is expected (Winand, 1991; Szymanowski, 1996). 3.1. The hematite process Fig. 4. Mini-thickener design.
feed concentrate and final LS2 residue samples were also analysed for sulfur speciation. From the mass balance, the predicted exit PLS concentrations from Leach Stage 1 in the goethite model experiments are 94 g/L Cu+, 1.9 g/L Cu2+ and 31 g/L Fe2+ ions. For the hematite model experiments the exit PLS concentrations from Leach Stage 1 are 96 g/L Cu+, 1.5 g/L Cu2+ and 121 g/L Fe2+ ions. The PLS analysis measured in this work was as expected in proportion to the extraction of Cu and Fe achieved. Although the reduced species in the PLS were 10% lower than predicted, due to the air oxidation of cuprous ion, the impact for either flowsheet is not problematic. 2.5. pH and redox measurement pH measurements were only taken at room temperature in the filtered samples using a refillable combination electrode with a ceramic junction. The pH measurements have not been corrected for liquid junction potential, and were generally near pH 0 or lower. Hence, free acid titrations in the feed and final PLS provide
This model focuses on 3 major process units (see Fig. 1), a 2 stage counter-current leach, copper solvent extraction and iron precipitation in an autoclave. The input and output streams for LS1, LS2, SX and Table 2 Hematite process streams Stream From autoclave to Leach Stage 2 From Leach Stage 2 to Leach Stage 1 From Leach Stage 1 to solvent extraction From solvent extraction to autoclave
Cu+ (g)
Cu2+ (g)
Fe2+ (g)
Fe3+ (g)
0
50.3
0
80.2
0
73.0
99.6
0.5
95.5
1.5
121.3
0
2.0
48.3
121.3
0
Feed, 100% CuFeS2 (135 g), Extent of CuFeS2 leaching: LS1 = 51.5%; LS2 = 48.5%. Solution contains 110 g CaCl2; 2 g HCl; 1000 g H2O.
J. Liddicoat, D. Dreisinger / Hydrometallurgy 89 (2007) 323–331 Table 3 Goethite process streams Stream From solvent extraction to Leach Stage 2 From Leach Stage 2 to leach stage 1 From Leach Stage 1 to solvent extraction
Cu+ (g)
Cu2+ (g)
Fe2+ (g)
Fe3+ (g)
0
48.7
31.1
0
0
69.7
0.3
93.5
1.9
31.1
8.2 0
Feed, 100% CuFeS2 (135 g), Extent of CuFeS2 leaching: LS1 = 55%; LS2 = 45%. Solution contains 110 g CaCl2; 2 g HCl; 1000 g H2O.
327
with the hematite model, the input and output stream data is shown in Table 3 and assumed reactions are shown by Eqs. (8)–(15). Stage 2 (LS2) CuFeS2 þ 3CuCl2 →4CuCl þ FeCl2 þ 2So
ð8Þ
2CuCl þ 0:5O2 þ 2HCl→2CuCl2 þ H2 O
ð9Þ
2FeCl2 þ 0:5O2 þ 2HCl→2FeCl3 þ H2 O
ð10Þ
2FeCl3 þ 4H2 O→2FeOOHðsÞ þ 6HCl
ð11Þ
autoclave determined from the mass balance for this flowsheet are shown in Table 2; and the assumed reactions for each unit operation are included as Equations (1)–(7) shown below. In reaction 4, only half the copper is extracted due to balancing the acid generated with the acid required for the oxidation of cuprous to cupric. Note also that not all iron is precipitated in the autoclave, as ferric ions return to Leach Stage 2 as an oxidant for leaching. Leach Stage 2 (LS2)
ð10 and 11Þ2FeCl2 þ 0:5O2 þ 3H2 O→2FeOOHðsÞ þ4HCl ð12Þ
CuFeS2 þ 4FeCl3 →5FeCl2 þ CuCl2 þ 2So
2CuCl þ 0:5O2 þ 2HRorg →CuR2org þ CuCl2 þ H2 O
ð1Þ
Leach Stage 1 (LS1) CuFeS2 þ 4FeCl3 →5FeCl2 þ CuCl2 þ 2So
ð13Þ
CuFeS2 þ 3CuCl2 →4CuCl þ FeCl2 þ 2So
ð14Þ
Solvent extraction (SX)
ð15Þ
Leach Stage 1 (LS1) CuFeS2 þ 4FeCl3 →5FeCl2 þ CuCl2 þ 2So
ð2Þ
CuFeS2 þ 3CuCl2 →4CuCl þ FeCl2 þ 2So
ð3Þ
Solvent extraction (SX) 2CuCl þ 0:5O2 þ 2HRorg →CuR2org þ CuCl2 þ H2 O ð4Þ Hematite precipitation in autoclave (A/C) 2FeCl2 þ 0:5O2 þ 2H2 O→Fe2 O3ðsÞ þ 4HCl
ð5Þ
2CuCl þ 0:5O2 þ 2HCl→2CuCl2 þ H2 O
ð6Þ
2FeCl2 þ 0:5O2 þ 2HCl→2FeCl3 þ H2 O
ð7Þ
3.2. The Goethite process This process focuses only on 2 major process units (see Fig. 2), and despite being simpler in overall flowsheet design than the hematite model, the leach is more complex as oxygen or air is added to precipitate goethite in LS2 thus producing a mixed sulfur/iron residue. As
3.3. Testwork matrix for the counter-current leach experiments Twelve continuous counter-current leach experiments were performed. The order, model basis and conditions used are shown in Table 4. The experimental identifier indicates upon which process model the leach Table 4 Order of experiments Expt.
Feed concentrate
RT (h)
Total time (h)
Temp. (°C)
Air/O2 to LS2 (flow rate)
H1 H2 H3 H4 H5
Antamina
2 2 3 3 3
10.75 10 18 18 18
85 95 85 95 95
No No No No No
2 3 2 2 2 3
12 18 12 10 10 18
95 85 85 85 95 95
No No No Air (200 mL/min) Air (2.5 L/min) O2 (2.5 L/min)
3
17.5
95
No
H6 H7 H8 G1 G2 G3 H9
↓
FG Antamina
↓
Antamina
↓
FG Antamina FG Rosario
RT = residence time per leach stage.
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Table 5 Feed solutions for hematite model experiments Experiment Feed solution to leach stage 2
H1 H2 H3 H4 H5 H6 H7 H8
Cl− [M]
E mV Ag/ pHa AgCla
7.2 7.4 7.2 8.0 6.3 6.4 8.0 7.2
648 650 639 661 677 660 659 661
− 0.48 − 0.24 − 0.36 − 0.35 − 0.16 − 0.25 − 0.68 − 0.67
Cu2+ g/L
Fe3+ g/L
Free acid (as HCl) g/L
47.8 47.2 52.9 55.8 45.0 41.1 47.7 48.0
76.7 79.9 87.2 90.6 76.0 70.2 80.1 75.3
5.7 5.3 4.0 4.0 2.7 1.9 3.0 3.7
a
Measured at room temperature.
was based, ‘H’ representing the hematite process and ‘G’ the goethite process. The residence time (RT) quoted in the table is per each leach stage, and the total time for each experiment was for 2–3 total (2 stage) leach cycles. The aim of these experiments was to find conditions to achieve maximum copper extraction (N95%) with both models by varying conditions of residence time, temperature and particle size. The first eleven experiments were conducted using Antamina concentrate and the final experiment was performed using finely ground Rosario concentrate, at the optimum conditions determined from the previous experiments. Analyses of feed liquor introduced to Leach Stage 2 are reported in Tables 5, 7 and 9. Copper and iron extraction was determined by the difference between the analysis of the feed solids and the final bulk solid residues leaving Leach Stage 2. 4. Results and discussion 4.1. Results of hematite model experiments
Fig. 5. Cu and Fe (%) Extraction over several leach cycles for Experiment H5 [P80 = 41 μm, 3 h per leach stage at 95 °C].
time and temperature. The first four experiments employed “as received” Antamina concentrate (P90 = 75 μm), whilst the successive four experiments employed finely ground concentrate (P90 = 41 μm). These experiments revealed that increasing the temperature from 85 °C to 95 °C had a greater impact on extraction than increasing the residence time from 2 h to 3 h. For the first four experiments, the highest copper extraction achieved was 93%, employing a 3 h leach stage residence time at 95 °C. As N 95% copper extraction in chloride media has been well demonstrated by others (Winand, 1991; Dutrizac, 1992), the subsequent experiments H5-H8 were performed on the finer material in order to achieve higher copper extraction. Here, the highest copper extraction was 98%, employing a 3 h leach stage residence time at 95 °C (H5), and plots of Cu and Fe % extractions and Cu and Fe the final leach residue can be seen over several leach cycles in Figs. 5 and 6. Experiments H6 and H7 with
The results of eight experiments based on the hematite leach model are shown in Table 6 with varying residence Table 6 Results for Hematite model experiments Experiment
H1 H2 H3 H4 H5 H6 H7 H8
Exit PLS solution from LS1
Final LS2 residue
CuTotal g/L
FeTotal g/L
Cu% extn
Fe% extn
74.1 81.8 86.3 94.6 86.0 75.3 81.1 80.4
101.7 114.3 125.1 127.9 118.0 103.9 112.9 106.5
80 87 83 93 98 96 96 90
74 80 76 85 91 88 89 83
Fig. 6. Cu and Fe in LS2 Residue over several leach cycles from Experiment H5 [P80 = 41 μm, 3 h per leach stage at 95 °C].
J. Liddicoat, D. Dreisinger / Hydrometallurgy 89 (2007) 323–331
329
Table 7 Feed solutions for Goethite model experiments Experiment Feed Solution to Leach Stage 2 Cl- E pH [M] mV Ag/ Ag/ Cl a G1 G2 G3
4.5 5.7 5.6
Cu2+ Fe3+ Fe2+ CaCl2 Free Acid g/L g/L g/L g/L (as HCl) g/L
463 0.02 54.1 7.9 27.1 110 457 − 0.47 55.9 11.6 22.9 220 443 − 0.29 47.4 4.9 25.1 220
0.7 10.0 b0.01
Due to the high air/oxygen flow rate (in G2 and G3) the temperature of the leach was depressed by approximately 4 °C from the starting water bath temperature down to 91 °C. a Measured at room temperature.
shorter residence time or lower temperature, both reported copper extractions of 96%. The % extraction Cu and Fe, and the Cu and Fe remaining in the final residue remained constant +/− 1% over several leach cycles after the first cycle. The lower values reported for iron extraction in Table 6 (74%– 91%) were found to represent iron remaining as undisturbed pyrite (FeS2) in addition to iron remaining from unleached chalcopyrite (CuFeS2). 4.2. Results of Goethite model experiments Three experiments based on the goethite leach model were performed, and the feed conditions and extraction results are shown in Tables 7 and 8. In the first two experiments air was added to Leach Stage 2 to regenerate cupric ions for further leaching and ferric ions for goethite precipitation. However, both of these experiments were not successful in achieving high copper extractions, indicating insufficient re-oxidation of Fe3+ or Cu2+ ions. For the third experiment, G3, finely ground concentrate and 98% oxygen were used to achieve higher copper extraction of 89% with a 3 h residence time at 95 °C. Following the first three cycles in experiment G3, copper extraction stabilized at 89% (see Fig. 7) and a much higher oxidation potential was recorded in Leach Stage 2. A high oxygen gas flow rate Table 8 Results for Goethite model experiments Experiment
G1 G2 G3
Fig. 7. Cu and Fe (%) Extraction over several leach cycles for Experiment G3 [P80 = 37 μm, 3 h per leach stage at 95 °C].
overcomes oxygen solubility inefficiency limitations at the bench scale. However, an industrial scale reactor can be designed to increase oxygen utilization efficiency using air. It was also intended that the feed liquor contain a low concentration (b 3 g/L) of free acid (as HCl) to promote goethite precipitation. Experiment G2 however had 10.0 g/L HCl resulting in inefficient iron precipitation and no better copper extraction. Though the goethite leach experiments were not successful in achieving N 95% copper extraction there is potential for doing so with further work. 4.3. Application of hematite leach model to Rosario concentrate A final experiment was conducted based on the Hematite Process leach model using finely ground Rosario concentrate (P90 = 37 μm) with a leach stage residence time of 3 h at 95 °C. The Rosario concentrate contains a similar amount of copper (26.8%) as the Antamina concentrate (28.5%), but less chalcopyrite and more chalcocite. Experimental feed conditions and extraction results are shown in Table 9. Surprisingly, not only was the final copper extraction 98%, but by the end of the first Table 9 Feed conditions and extraction results for the H9 Rosario experiment
Exit PLS Solution from LS1
Final LS2 Residue
CuTotal g/L
FeTotal g/L
Cu% Extn
Fe% extn
55.5 87.9 93.9
27.6 59.7 26.2
60 67 89
13 53 −7
Expt. Stream Solution
Solids
Percentage extn
Cu g/L Fe g/L Mass g Cu % Fe % Cu % Fe % H9
Feed LS1 LS2
50.6 91.7 55.1
82.0 100.5 84.9
135 76.3 68.6
26.8 2.1 1.1
26.8 28.3 27.5
96 98
40 48
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Table 10 Trace metal analysis Element
Ag Cr Pb Mg Ni Zn
Extraction % based on final LS2 residue H5
G3
H9 (Rosario)
97.1 92.1 99.9 96.7 93.0 98.9
92.4 46.2 99.7 93.4 90.1 98.4
98.9 93.9 94.3 95.5 92.4 98.7
background salt may be possible for the hematite model as there is no iron precipitation in the leach, and hence there is no concern for jarosite formation. The goethite model experiments only achieved 89% copper extraction under comparable optimum conditions. However, longer residence times or finer grinding to 20 microns or the use of an autoclave for Leach Stage 2 may increase copper extraction, as is required for some competing sulfate based leach processes. Acknowledgements
leach stage 96% extraction had already been achieved. The presence of less refractory Cu2S along with pyrite in the concentrate contribute to the significantly decreased leaching time (Eqs. (16) and (17)). Cu2 S þ 2FeCl3 →2FeCl2 þ 2CuCl þ So
ð16Þ
Cu2 S þ 2CuCl2 →4CuCl þ So
ð17Þ
4.4. Trace metals All the elements reported in ICP analysis were examined to determine which other elements were leached with copper. Table 10 reports the extraction values of these elements in the final LS2 residues of three experiments. Silver (Ag), lead (Pb), nickel (Ni) and zinc (Zn) all reported significantly high extractions above 90%. This indicates the high suitability of chloride leaching for most complex sulfides. 5. Conclusions Two new process flowsheets have been developed, the Goethite Process and the Hematite Process, which combine Cu(II)/chloride leaching for copper with solvent extraction, to selectively transfer copper to a conventional sulfate electrowinning circuit. Solvent extraction (SX) is a known and effective method for selective uptake of copper for transfer to an electrowinning circuit with minimal impurity carry-over. However, the carry-over of chloride ion needs further investigation. With respect to iron deportment the flowsheets offer flexibility. As goethite (FeOOH) is a less stable iron residue in the environment than hematite (Fe2O3) it is important to have two process options because in some localities goethite will not be accepted in waste for disposal. The counter-current leach experiments performed for the hematite model achieved N95% copper extractions using a relatively straight forward 2-stage leach and the separation of sulfur leach residue from iron precipitate. The substitution of NaCl for CaCl2 as
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