a novel process for copper concentrates

David G Dixon, UBC HydrometallurgyDavid G Dixon, UBC HydrometallurgyGALVANOXGALVANOXTMTM – A Novel Process for Copper Concentrates – A Novel Process for Copper Concentrates

GALVANOXGALVANOXTMTM

A Novel Process for the TreatmentA Novel Process for the Treatmentof Copper Concentrates of Copper Concentrates

David G. DixonDavid G. DixonUBC Hydrometallurgy UBC Hydrometallurgy


GALVANOX HISTORY

GALVANOX FEATURES

GALVANOX CHEMISTRY

BATCH LEACHING RESULTS

PILOT LEACHING RESULTS

PROCESS FLOWSHEET OPTIONS

PROCESS COMPARISONS

COMMERCIAL EVALUATION

CONCLUSIONS

PRESENTATION OUTLINE


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.

GALVANOX HISTORY


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

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 FEATURES


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:

CuFeS2 + 2 Fe2(SO4)3 → CuSO4 + 5 FeSO4 + 2 S0

This reaction may be represented as a combination of anodic and cathodic half-cell reactions:

Anodic: CuFeS2 → Cu2+ + Fe2+ + 2 S0 + 4 e–

Cathodic: 4 Fe3+ + 4 e– → 4 Fe2+

GALVANOX CHEMISTRY


UNASSISTED CHALCOPYRITE LEACHING

Cu2+

Fe2+

4 Fe3+

4 Fe2+

So

4 e-

CuFeS2

Anodic Site Cathodic Site


UNASSISTED CHALCOPYRITE LEACHING


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.

GALVANOX CHEMISTRY


GALVANICALLY-ASSISTEDCHALCOPYRITE LEACHING

Cu2+

Fe2+

So

Py

Py

Cp

4 e- 4 e-

4 Fe3+

4 Fe2+

Anodic Site Cathodic Site


GALVANICALLY-ASSISTEDCHALCOPYRITE LEACHING

Partially leached particle Completely leached particles


The ferric required for GALVANOX leaching is regenerated in situ with oxygen gas

Ferric leaching of chalcopyrite:

CuFeS2 + 2 Fe2(SO4)3 → CuSO4 + 5 FeSO4 + 2 S0

Oxidation of ferrous with dissolved oxygen gas:

4 FeSO4 + O2 + 2 H2SO4 → 2 Fe2(SO4)3 + 2 H2O

Overall leaching reaction:

CuFeS2 + O2 + 2 H2SO4 → CuSO4 + FeSO4 + 2 S0 + 2 H2O

GALVANOX CHEMISTRY


GALVANOX leaching is followed by conventional solvent extraction and electrowinning to recover LME Grade A pure copper cathodes

Copper electrowinning:

CuSO4 + H2O → Cu0 + ½ O2 ↑ + H2SO4

GALVANOX CHEMISTRY


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:

4 FeSO4 + O2 + 4 H2O → 2 Fe2O3 (s) + 4 H2SO4

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 acid-consuming gangue minerals in the concentrate

GALVANOX CHEMISTRY


In summary, the overall GALVANOX process chemistry is as follows:

Galvanically-assisted atmospheric leaching of chalcopyrite:

CuFeS2 + O2 + 2 H2SO4 → CuSO4 + FeSO4 + 2 S0 + 2 H2O

Iron oxyhydrolysis:

FeSO4 + ¼ O2 + H2O → ½ Fe2O3 (s) + H2SO4

Copper electrowinning:

CuSO4 + H2O → Cu0 + ½ O2 ↑ + H2SO4

Overall process chemistry:

CuFeS2 + 5/4 O2 → Cu0 + 2 S0 + ½ O2 ↑ + ½ Fe2O3 (s)

GALVANOX CHEMISTRY


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


CHALCOPYRITE CONCENTRATE – 35% CuEffect of pyrite addition (50 g con, 65 g acid, 470 mV, 80°C)

0%

10%

20%

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50%

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70%

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100%

0 4 8 12 16 20 24

Time (h)

Cu

Rec

over

y

Py = 150 g (K5)Py = 100 g (K9)Py = 50 g (K6)Py = 25 g (K10)Py = 0 g (K1)


CHALCOPYRITE CONCENTRATE – 35% CuEffect of sulfuric acid addition (50 g con, 100 g Py, 470 mV, 80°C)

0%

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0 4 8 12 16 20 24

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Cu

Rec

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y

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%

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100%

0 4 8 12 16 20 24

Time (h)

Cu

Rec

over

y

E = 485 mV (K20)E = 470 mV (K16)E = 455 mV (K19)E = 440 mV (K18)E = 425 mV (K17)

CHALCOPYRITE CONCENTRATE – 35% CuEffect of solution potential (50 g con, 100 g Py, 90 g acid, 80°C)


400

410

420

430

440

450

460

470

480

490

500

0 4 8 12 16 20 24

Time (h)

Sol

utio

n P

oten

tial (

mV

vs

Ag/

AgC

l)CHALCOPYRITE CONCENTRATE – 35% Cu

Effect of solution potential (50 g con, 100 g Py, 90 g acid, 80°C)


0%

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0 4 8 12 16 20 24

Time (h)

Cu

Rec

over

y

T = 80°C (K16)T = 70°C (K22)T = 60°C (K21)

CHALCOPYRITE CONCENTRATE – 35% CuEffect of temperature (50 g con, 100 g Py, 90 g acid, 470 mV)


0%

10%

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0 4 8 12 16 20 24

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Cu

Rec

over

y

Baseline (K16)Alt. Baseline (K25A)+ K25A Continued (K25B)+ K5 Residue + 7.5 g Cu (K24)+ K8 Residue (K23)

CHALCOPYRITE CONCENTRATE – 35% CuEffect of pyrite recycle (50 g con, 100 g Py, 90 g acid, 470 mV, 80°C)


0 4 8 12

Time (h)

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

pH

0%

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0 4 8 12

Time (h)

Cu

Rec

over

y

Alt. Baseline (K25A)

+ K25A Continued (K25B)

+ K5 Residue + 7.5 g Cu (K24)

CHALCOPYRITE CONCENTRATE – 35% CuAt constant solution potential, pH is an indicator of reaction progress


0%

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0 4 8 12 16 20 24

Time (h)

Cu

Rec

over

y

Galvanox Leaching

No Pyrite

CHALCOPYRITE CONC 2 – 23.6% CuEffect of pyrite addition (30 g con, 120 g Py, 30 g acid, 480 mV, 80°C)


0%

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0 4 8 12 16 20 24

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Rec

over

y

Galvanox Leaching

No Pyrite



0%

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0 4 8 12 16 20 24

Time (h)

Cu

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over

yCHALCOPYRITE BULK CONC – 10.2% Cu

150 g bulk con @ ~1.21 Py/Cp ratio, 75 g acid, 440 mV, 80°C)


BULK CONC RESIDUE – 22.8 g/t Au77 g Galvanox residue @ 0.5 g/L NaCN, pH 11, room temp

0%

10%

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30%

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100%

0 12 24 36 48

Time (h)

Au

extra

ctio

n

0

1

2

3

4

5

6

0 12 24 36 48

Time (h)

NaC

N c

onsu

mpt

ion

(kg/

t)


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

SUMMARY OF LEACH RESULTS


FIRST GALVANOX COPPER (99.85% Cu directly from PLS at 50 g/L Fe!)


QUESTIONS ?

For more information, please visit:

www.GALVANOX.comwww.GALVANOX.com

a novel process for copper concentrates

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