GALVANOX TM A Novel Process for the Treatment of Copper Concentrates David G. Dixon UBC Hydrometallurgy
PRESENTATION OUTLINE GALVANOX HISTORY GALVANOX FEATURES GALVANOX CHEMISTRY BATCH LEACHING RESULTS PILOT LEACHING RESULTS PROCESS FLOWSHEET OPTIONS PROCESS COMPARISONS COMMERCIAL EVALUATION CONCLUSIONS
GALVANOX HISTORY UBC researchers Dave Dixon and Alain Tshilombo developed a novel process for galvanically-assisted atmospheric leaching of primary copper concentrates in early 2004. A preliminary patent application was filed in June 2004. Several patent applications were filed in 2005 (US, Chile, Peru, Laos), and successful PCT examination in September 2006 spawned many other national phase applications. UBC entered into an exclusive marketing agreement with Bateman Engineering in October 2006, and is working closely with Bateman to identify potential applications of the process. Batch testing programs on many candidate concentrates have been initiated or completed, continuous leaching was piloted in May, and three detailed feasibility studies are currently underway, with integrated pilot campaigns planned to begin in November.
Atmospheric Leach (~80 C) No microbes Pure sulphate medium (no chloride) Conventional materials of construction No fine grinding Generates elemental sulfur (> 95%), low oxygen demand No surfactants GALVANOX FEATURES Selective for chalcopyrite over pyrite (can cost-effectively treat low grade concentrates down to 9% copper or less) Complete copper recovery, typically in less than 12 hours, and sometimes in as little as 4 hours Fully compatible with conventional SX-EW
GALVANOX CHEMISTRY GALVANOX takes advantage of the galvanic effect between chalcopyrite and pyrite. Chalcopyrite is a semiconductor, and therefore corrodes electrochemically in oxidizing solutions. In ferric sulphate media, the overall leaching reaction is as follows: CuFeS 2 + 2 Fe 2 (SO 4 ) 3 CuSO 4 + 5 FeSO 4 + 2 S 0 This reaction may be represented as a combination of anodic and cathodic half-cell reactions: Anodic: CuFeS 2 Cu 2+ + Fe 2+ + 2 S 0 + 4 e Cathodic: 4 Fe 3+ + 4 e 4 Fe 2+
UNASSISTED CHALCOPYRITE LEACHING So Cu2+ 4 e- 4 Fe3+ Fe2+ CuFeS2 4 Fe2+ Anodic Site Cathodic Site
UNASSISTED CHALCOPYRITE LEACHING
GALVANOX CHEMISTRY Typically, chalcopyrite surfaces are passivated (i.e., they become resistant to electrochemical breakdown) in ferric sulfate solutions at even modest solution potential levels. It is widely held that this results from the formation of some sort of passivating film on the mineral surface that most likely consists of an altered, partially Fe-depleted sulfide layer. Because of this, most investigators have assumed that it is the anodic half-cell reaction that limits the overall rate of leaching. However, we discovered that it is primarily the cathodic half-cell reaction (i.e., ferric reduction) that is slow on the passivated chalcopyrite surface.
GALVANOX CHEMISTRY The presence of pyrite facilitates chalcopyrite leaching by providing an alternative surface for ferric reduction This essentially eliminates cathodic passivation of chalcopyrite in ferric sulfate solutions. Also, by ensuring rapid chalcopyrite oxidation, the solution potential is easily maintained at levels low enough to prevent anodic passivation of the chalcopyrite This also prevents anodic breakdown of the pyrite, which remains more or less completely inert.
GALVANICALLY-ASSISTED CHALCOPYRITE LEACHING Cu2+ Py Cp 4 Fe3+ 4 e- 4 e - 4 Fe 2+ Fe 2+ Anodic Site So Py Cathodic Site
GALVANICALLY-ASSISTED CHALCOPYRITE LEACHING Partially leached particle Completely leached particles
GALVANOX CHEMISTRY The ferric required for GALVANOX leaching is regenerated in situ with oxygen gas Ferric leaching of chalcopyrite: CuFeS 2 + 2 Fe 2 (SO 4 ) 3 CuSO 4 + 5 FeSO 4 + 2 S 0 Oxidation of ferrous with dissolved oxygen gas: 4 FeSO 4 + O 2 + 2 H 2 SO 4 2 Fe 2 (SO 4 ) 3 + 2 H 2 O Overall leaching reaction: CuFeS 2 + O 2 + 2 H 2 SO 4 CuSO 4 + FeSO 4 + 2 S 0 + 2 H 2 O
GALVANOX CHEMISTRY GALVANOX leaching is followed by conventional solvent extraction and electrowinning to recover LME Grade A pure copper cathodes Copper electrowinning: CuSO 4 + H 2 O Cu 0 + ½ O 2 + H 2 SO 4
Iron is rejected from the Galvanox circuit by oxyhydrolysis in an autoclave at ~220 C to make hematite, which is easy to filter and perfectly suitable for disposal Iron oxyhydrolysis: GALVANOX CHEMISTRY 4 FeSO 4 + O 2 + 4 H 2 O 2 Fe 2 O 3 (s) + 4 H 2 SO 4 This autoclave also treats a portion of the concentrate feed, in order to generate the heat required for the atmospheric leach circuit, and also to generate extra acid as required for secondary sulfides or acidconsuming gangue minerals in the concentrate
GALVANOX CHEMISTRY In summary, the overall GALVANOX process chemistry is as follows: Galvanically-assisted atmospheric leaching of chalcopyrite: CuFeS 2 + O 2 + 2 H 2 SO 4 CuSO 4 + FeSO 4 + 2 S 0 + 2 H 2 O Iron oxyhydrolysis: FeSO 4 + ¼ O 2 + H 2 O ½ Fe 2 O 3 (s) + H 2 SO 4 Copper electrowinning: CuSO 4 + H 2 O Cu 0 + ½ O 2 + H 2 SO 4 Overall process chemistry: CuFeS 2 + 5 / 4 O 2 Cu 0 + 2 S 0 + ½ O 2 + ½ Fe 2 O 3 (s)
BATCH TESTING APPARATUS Six 3-L jacketed reactors Water baths for temperature control Digital oxygen mass flow meters for potential control Automated data acquisition for potential, ph and temperature
Cu Recovery CHALCOPYRITE CONCENTRATE 35% Cu Effect of pyrite addition (50 g con, 65 g acid, 470 mv, 80 C) 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 0 4 8 12 16 20 24 Time (h) Py = 150 g (K5) Py = 100 g (K9) Py = 50 g (K6) Py = 25 g (K10) Py = 0 g (K1)
Cu Recovery CHALCOPYRITE CONCENTRATE 35% Cu Effect of sulfuric acid addition (50 g con, 100 g Py, 470 mv, 80 C) 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Ac = 90 g (1.80 kg/kg) (K16) Ac = 80 g (1.60 kg/kg) (K14) Ac = 68 g (1.36 kg/kg) (K9) Ac = 55 g (1.10 kg/kg) (K13) Ac = 45 g (0.90 kg/kg) (K15) 0 4 8 12 16 20 24 Time (h)
Cu Recovery CHALCOPYRITE CONCENTRATE 35% Cu Effect of solution potential (50 g con, 100 g Py, 90 g acid, 80 C) 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 0 4 8 12 16 20 24 Time (h) E = 485 mv (K20) E = 470 mv (K16) E = 455 mv (K19) E = 440 mv (K18) E = 425 mv (K17)
Solution Potential (mv vs Ag/AgCl) CHALCOPYRITE CONCENTRATE 35% Cu Effect of solution potential (50 g con, 100 g Py, 90 g acid, 80 C) 500 490 480 470 460 450 440 430 420 410 400 0 4 8 12 16 20 24 Time (h)
Cu Recovery CHALCOPYRITE CONCENTRATE 35% Cu Effect of temperature (50 g con, 100 g Py, 90 g acid, 470 mv) 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 0 4 8 12 16 20 24 Time (h) T = 80 C (K16) T = 70 C (K22) T = 60 C (K21)
Cu Recovery CHALCOPYRITE CONCENTRATE 35% Cu Effect of pyrite recycle (50 g con, 100 g Py, 90 g acid, 470 mv, 80 C) 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Baseline (K16) Alt. Baseline (K25A) + K25A Continued (K25B) + K5 Residue + 7.5 g Cu (K24) + K8 Residue (K23) 0 4 8 12 16 20 24 Time (h)
Cu Recovery David G Dixon, UBC Hydrometallurgy ph CHALCOPYRITE CONCENTRATE 35% Cu At constant solution potential, ph is an indicator of reaction progress 100% 1.4 90% 80% 70% 1.3 1.2 60% 1.1 50% 40% 1 30% 20% 10% 0% Alt. Baseline (K25A) + K25A Continued (K25B) + K5 Residue + 7.5 g Cu (K24) 0 4 8 12 Time (h) 0.9 0.8 0.7 0 4 8 12 Time (h)
Cu Recovery CHALCOPYRITE CONC 2 23.6% Cu Effect of pyrite addition (30 g con, 120 g Py, 30 g acid, 480 mv, 80 C) 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Galvanox Leaching No Pyrite 0 4 8 12 16 20 24 Time (h)
Cu Recovery CHALCOPYRITE CONC 3 24.1% Cu Effect of pyrite addition (10 g con, 40 g Py, 15 g acid, 470 mv, 80 C) 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Galvanox Leaching No Pyrite 0 4 8 12 16 20 24 Time (h)
Cu Recovery CHALCOPYRITE CONC 4 20.1% Cu Effect of pyrite addition (57 g con, 112 g Py, 60 g acid, 450 mv, 80 C) 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Galvanox Leaching No Pyrite 0 4 8 12 16 20 24 Time (h)
Cu Recovery CHALCOPYRITE BULK CONC 10.2% Cu 150 g bulk con @ ~1.21 Py/Cp ratio, 75 g acid, 440 mv, 80 C) 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 0 4 8 12 16 20 24 Time (h)
Au extraction David G Dixon, UBC Hydrometallurgy NaCN consumption (kg/t) BULK CONC RESIDUE 22.8 g/t Au 77 g Galvanox residue @ 0.5 g/l NaCN, ph 11, room temp 100% 6 90% 80% 5 70% 4 60% 50% 3 40% 30% 2 20% 1 10% 0% 0 12 24 36 48 0 0 12 24 36 48 Time (h) Time (h)
SUMMARY OF LEACH RESULTS GALVANOX is robust (insensitive to the source of chalcopyrite) Process optimization is straightforward: Pyrite-to-chalcopyrite ratio (2:1 to 4:1 typically optimal) Acid concentration (stoichiometric + modest excess) Solution potential (> 440 mv) Temperature (> 70 C) Recycled pyrite is equally as effective as fresh pyrite Under the correct process conditions, GALVANOX leaching is very rapid (limited by the rate of gas-liquid mixing) High Au extractions from GALVANOX residues are feasible, with relatively modest cyanide consumption levels
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