david dreisinger presentation - peru october 2012 - reduced
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New Developments in the Treatment of Sulphides
David Dreisinger
University of British Columbia
Vancouver, Canada
Outline
• Where have we come from? – a selected history
• What has been happening recently?
• Where might we go in the future?
• Focus on Copper
Where have we been?
• Copper
– Chloride leaching of copper – CLEAR Process and BHAS Process
– Heap leach SX-EW for oxides and secondary sulphides
– Ammonia leaching of copper - Escondida Process (Coloso) and Arbiter Process
– Nitrogen species catalyzed leaching of copper (NSC)
– Mount Gordon Copper Process
– Total Pressure Oxidation Process (Bagdad and Kansanshi)
– Medium Temperature Pressure Leach Process (Morenci)
– BIOCOP Process for Copper (Chile)
– CESL Copper Process (UHC Plant in Brazil)
Heap Leach Pad Under Preparation
Heap Leach Under Irrigation
SX-EW Mixer Settlers and Tank Farm
Copper Electrowinning Tankhouse
BIOCOP Plant Overview
8
Bagdad Demonstration Plant (Total Oxidation)
9
Where have we come from?
• Base metal and precious metal innovations
• Necessity (Mt. Gordon, Sepon, Cobre Las Cruces) and Opportunity (Total POX at Bagdad)
• Successful application of hydromet unlike non-sulphides….
• Many unique plants
• Enabled by other technologies
– Solvent extraction
– Ion exchange
– Electrowinning
– Hydrogen reduction of metals
– Bioprocessing
– Materials of construction
– Etc.
10
Where are we going?
• All the easy ores are gone (or are already being processed)?
• Demand for materials continues to rise (China, India, Brazil, etc.)
• Prices have risen which continues to make lower grade materials attractive
• Metallurgists have to adapt to new realities and innovate
11
What has been happening recently?
• New innovations in all areas
• Levers for innovation;
– High temperature
– High pressure
– Use of catalysts (nitric/nitrous acid, chloride)
– Use of complexants (ammonia, chloride, etc.)
– Control of sulfur behaviour (surfactants)
– Iron precipitation chemistry
– Atmospheric leaching
– Ultra fine grinding
– Galvanic systems for leaching
– New separation and metal recovery technologies
12
Examples of Innovation
• Sepon Copper Process (Laos) – paper only
• PLATSOL Process (NorthMet Project, USA)
• GALVANOX Process (UBC – David Dixon)
13
SEPON Copper Plant
PLATSOL™ PROCESS
• Process developed initially for PolyMet Mining Corporation by Chris Fleming, David Dreisinger and Terry O’Kane
15
PLATSOL Principles
• PLATSOL™ Process
– Simple process for one-step dissolution of base and precious metals
– Invented at Lakefield Research
– Tested via Batch and Continuous Autoclave Programs at Lakefield
– High levels of base (+95-99%) and precious metals (90-95%) recovery
Bulk Flotation (Applied to NorthMet Ore – PolyMet Mining)
Pressure Oxidation: Conventional and PLATSOL Metal Extractions (220 C)
Element Conventional PLATSOL**
Cu 99.3 99.6
Ni 95.9 98.9
Co >92 96
Fe 11.5 11.5
S 91.5 91.5
Pt ~0 96
Pd 61.1 94.6
Au ~0 89.4
** ACTUAL PILOT PLANT RESULTS FROM LAKEFIELD
Under PlatSol leaching conditions all value metals are efficiently dissolved
Addition of Chloride to High Temperature Pressure Oxidation to Promote Leaching of Precious and Base Metals.
PGM’s, Copper, Nickel and Cobalt can then be selectively extracted
The following slides show the chemistry of PLATSOL
PLATSOL™ Principles
Autoclave Leaching Base Metals
Chloride – Assisted Total Pressure Oxidation
Chalcopyrite Oxidation/Iron Hydrolysis:
CuFeS2 + 4.25O2 + H2O = CuSO4 + 0.5Fe2O3 + H2SO4
Pyrite Oxidation:
FeS2 + 3.75O2 + 2H2O = 0.5Fe2O3 + 2H2SO4
Pyrrhotite Oxidation
Fe7S8 + 16.25O2 + 8H2O = 3.5Fe2O3 + 8H2SO4
Nickel Sulfide Oxidation:
NiS + 2O2 = NiSO4
Basic Ferric Sulfate Formation:
Fe2O3 + 2H2SO4 = 2Fe(OH)SO4 + H2O
Autoclave Leaching Precious Metals
Gold Oxidation/Chlorocomplex Formation:
Au + 0.75O2 + 4HCl = HAuCl4 + 1.5H2O
Platinum Oxidation/Chlorocomplex Formation:
Pt + O2 + 6HCl = H2PtCl6 + 2H2O
Palladium Oxidation/Chlorocomplex Formation:
Pd + 0.5O2 + 4HCl = H2PdCl4 + H2O
Temperature of 220 to 230 C.
Barren solids washed and discarded
14121086420
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Eh (Volts)
pH
Au
Au(OH)3
AuCl4-
Eh – pH Diagram for the Au-Cl system at 25 C. [Au] = 0.00001 M. [Cl] = 0.2 M.
PLATSOL™ Principles
14121086420
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Eh (Volts)
pH
Pd
PdO
PdCl+
Eh – pH Diagram for the Pd-Cl system at 25 C.[Pd] = 0.00001 M. [Cl] = 0.2 M.
PLATSOL™ Principles
14121086420
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Eh (Volts)
pH
Pt PtO
PtO2
PtCl6-2
Eh – pH Diagram for the Pt-Cl system at 25 C.[Pt] = 0.00001 M. [Cl] = 0.2 M.
PLATSOL™ Principles
Optimization Tests
Optimization Tests
Base Metal Recovery
Copper
• Copper Solvent Extraction and Electrowinning
to Produce LME Grade Copper Metal Cathode
Nickel/Cobalt
• Variety of Processes Possible
• Mixed Hydroxide Precipitation of Nickel and Cobalt
• Nickel and Cobalt Hydroxide Refined “Off Site”
• SX-EW or SX-Hydrogen Reduction to Metal
PLATSOL™ Principles
____________________________________________
Au Pt Pd
____________________________________________
Autoclave solution (mg/L) 0.32 0.34 1.23
Product solution (mg/L) 0.01 0.00 0.01
Precipitate ( g/t) 92 102 484
Precip. Efficiency % 97 ~100 99
____________________________________________
Precipitation of Precious Metals
* Precipitation with sodium hydrosulfide
PLATSOL™ Principles
Overall Process
Applications to Other Cu/Ni/PGM Concentrates
Applications to Other Cu/Ni/PGM Concentrates
Applications to Other Feeds
• Cu/Au concentrates
• Refractory Au Concentrates
• Cu/Ni/PGE mattes
• Pt Laterites
• Automobile catalysts
Other Applications
Cu - Au concentrate
(28.9% Cu,5.8 g/t Au)
PLATSOLTM recovery99.7% Cu
95.9% Au
No cyanide!
Other Applications
Refractory Au ores-concentrates (non-preg robbers)
FeS2 - FeAsS conc
19.9 Au, 19.4 g/t Ag
• PLATSOLTM recovery
Au 96%, Ag 99.5%
• No cyanide!
GALVANOX™ PROCESS
• Process developed by David Dixon with Alain Tshilombo and Ghazaleh Nazari
35
GALVANOX FEATURES
Atmospheric Leach (~80°C)
No microbes
Pure sulphate medium (no chloride)
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
Conventional materials of construction
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:
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+
Cu2+
Fe2+
4 Fe3+
4 Fe2+
So
4 e-
CuFeS2
Anodic Site Cathodic Site
UNASSISTED CHALCOPYRITE LEACHING
UNASSISTED CHALCOPYRITE LEACHING
GALVANOX RATE CONTROL
• Chalcopyrite appears passivated
• Anode passivation due to iron depleted sulphide
• Anode or cathode?
• Dixon and Tshilombo – passivation appears to be at cathode (ferric reduction)
• Pyrite catalyzes the cathodic process in galvanic leaching
• Pyrite is inert and can be recycled
Cu2+
Fe2+
So
Py
Py
Cp
4 e- 4 e-
4 Fe3+
4 Fe2+
Anodic Site Cathodic Site
GALVANICALLY ASSISTED CHALCOPYRITE LEACHING
Partially leached particle Completely leached particles
GALVANICALLY ASSISTED CHALCOPYRITE LEACHING
GALVANOX CHEMISTRY
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
Conventional SX-EW of Cu and Fe Precipitation
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)
BATCH TESTING
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
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 4 8 12 16 20 24
Time (h)
Cu
Re
co
ve
ry
Py = 150 g (K5)
Py = 100 g (K9)
Py = 50 g (K6)
Py = 25 g (K10)
Py = 0 g (K1)
CHALCOPYRITE CONCENTRATE #1 – 35% CuEffect of pyrite addition (50 g con, 65 g acid, 470 mV, 80 C)
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 4 8 12 16 20 24
Time (h)
Cu
Re
co
ve
ry
Galvanox Leaching
No Pyrite
CHALCOPYRITE CONCENTRATE #2 – 23.6 % CuEffect of pyrite addn (30 g con, 120 g Py, 30 g acid, 480 mV, 80 C)
0%
10%
20%
30%
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50%
60%
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80%
90%
100%
0 4 8 12 16 20 24
Time (h)
Cu
Re
co
ve
ry
Galvanox Leaching
No Pyrite
CHALCOPYRITE CONCENTRATE #3 – 24.1 % CuEffect of pyrite addn (10 g con, 40 g Py, 15 g acid, 470 mV, 80 C)
0%
10%
20%
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50%
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90%
100%
0 4 8 12 16 20 24
Time (h)
Cu
Re
co
ve
ry
Galvanox Leaching
No Pyrite
CHALCOPYRITE CONCENTRATE #4 – 20.1 % CuEffect of pyrite addn (57 g con, 112 g Py, 60 g acid, 450 mV, 80 C)
0%
10%
20%
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50%
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100%
0 4 8 12 16 20 24
Time (h)
Cu
Re
co
ve
ry
CHALCOPYRITE BULK CONCENTRATE – 10.2% Cu(150 g bulk con @ ~1.21 Py/Cp ratio, 75 g acid, 440 mV, 80 C)
KEY QUESTIONS
• ARE ALL PYRITES EQUAL? (NO!)
• CAN PYRITE BE IMPROVED IN CATALYTIC ABILITY? (YES –WITH A SILVER SURFACE TREATMENT)
• HOW DO YOU HAVE GALVANIC CONTACT WHEN THE CHALCOPYRITE GETS COATED IN ELEMENTAL SULPHUR (A NATURAL INSULATOR? (INTERESTING ANSWER!)
• WHAT ABOUT OTHER “REFRACTORY” COPPER SULPHIDES? (GALVANOX HAS BEEN ADAPTED TO TREATMENT OF ENARGITE)
51
52
Experiments (Ghazaleh Nazari – Ph.D.)
• Investigating the effect of various parameters on the kinetics of chalcopyrite leaching:
– Mass ratio of silver-enhanced Py/Cp
– Silver concentration on pyrite
– Solution potential
– Pyrite recycle
– Pulp density
• Comparison of silver-catalyzed leaching and silver-enhanced pyrite-catalyzed leaching
53
Unassisted chalcopyrite leaching
Potential set point = 470 mV (vs. Ag/AgCl), T = 80°C
0%
20%
40%
60%
80%
100%
0 10 20 30 40 50 60 70 80 90
Time (h)
Co
pp
er
Ex
tra
cti
on
54
ComparisonSilver-enhanced pyrite additionNatural pyrite addition
Potential set point = 470 mV (vs. Ag/AgCl), T = 80°C
0%
20%
40%
60%
80%
100%
0 20 40 60 80 100
Time (h)
Co
pp
er
Ex
tra
cti
on
Pyrite #1, Py/Cp = 6
Pyrite #2, Py/Cp = 6
Pyrite #3, Py/Cp = 60%
20%
40%
60%
80%
100%
0 2 4 6 8 10
Time (h)
Co
pp
er
Ex
tracti
on
Pyrite #3, Py/Cp = 6, Ag/Py = 100 ppm
Pyrite #1,Py/Cp = 6, Ag/Py = 100 ppm
Pyrite #2,Py/Cp = 6, Ag/Py = 100 ppm0%
20%
40%
60%
80%
100%
0 20 40 60 80 100
Time (h)
Co
pp
er
Ex
tracti
on
Py #1Py #2Py #3
Py #3, Ag/Py = 100 ppmPy #1, Ag/Py = 100 ppmPy #2, Ag/Py = 100 ppm
55
Recycled pyrite at low pulp density at different solution potentials
0%
20%
40%
60%
80%
100%
0 10 20 30 40 50 60
Time (h)
Co
pp
er
Ex
tracti
on
Py/Cp = 4, Ag/Py = 100 ppm, E = 450 mV
Py/Cp = 4, Ag/Py = 100 ppm, E = 440 mV
Py/Cp = 4, Ag/Py = 100 ppm, E = 470 mV
Py/Cp = 4, Ag/Py = 100 ppm, E = 420 mV0%
20%
40%
60%
80%
100%
0 10 20 30 40 50 60
Time (h)
Co
pp
er
Ex
tracti
on
Py/Cp = 4, Ag/Py = 100 ppm, E = 450 mV, Py Recycle
Py/Cp = 4, Ag/Py = 100 ppm, E = 440 mV, Py Recycle
Py/Cp = 4, Ag/Py = 100 ppm, E = 470 mV, Py Recycle
Py/Cp = 4, Ag/Py = 100 ppm, E = 420 mV, Py Recycle
10 g/L Cu concentrate, T = 80°C
Fresh pyrite Recycled pyrite
56
High pulp density
0%
20%
40%
60%
80%
100%
0 2 4 6 8 10
Time (h)
Co
pp
er
Ex
tracti
on
Py/Cp = 2, Ag/Py = 100 ppm, E = 450 mV, 2nd Py Recycle
Py/Cp = 2, Ag/Py = 100 ppm, E = 450 mV, Fresh Py
Py/Cp = 2, Ag/Py = 100 ppm, E = 450 mV, 1st Py Recycle
70 g/L Cu concentrate, T = 80°C
57
Silver Catalyzed Leaching
• The copper extraction from chalcopyrite increases in ferric sulfate solution by addition of silver as a soluble silver salt.
• Formation of an intermediate Ag2S film
CuFeS2 + 4 Ag+ → 2 Ag2S (chalcopyrite surface) +
Cu2+ + Fe2+
Ag2S + 2 Fe3+ → 2 Ag+ + 2 Fe2+ + S0
Silver-Catalyzed Leaching
• Silver availability
– Silver availability is affected by the formation of argentojarosite during leaching:
3Fe2(SO4)3 + Ag2SO4 + 12H2O → 2AgFe3(SO4)2(OH)6 + 6H2SO4
• Silver toxicity (in biological leaching)
– Accumulation of silver sulfide on ferrooxidant cells has been observed
– Silver ions are toxic to most microorganisms
– Biooxidant growth is inhibited in the presence of even miniscule amounts of silver (as low as 0.1 ppm)
58
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Comparison of silver-catalyzed leaching and enhanced pyrite-catalyzed leaching
0.61 g Ag/kg Cu, E = 450 mV, T = 80°C
0%
20%
40%
60%
80%
100%
0 20 40 60 80 100
Time (h)
Co
pp
er
Ex
tra
cti
on
Py/Cp = 2, Ag/Py = 100 ppm, E = 450 mV
Same Silver Added, No Pyrite Added, E = 450 mV0%
20%
40%
60%
80%
100%
0 20 40 60 80 100
Time (h)C
op
per
Ex
tracti
on
Py/Cp = 2, Ag/Py = 100 ppm, E = 450 mV, Py Recycle
Same Silver Added, No Pyrite Added, E = 450 mV
Fresh pyrite Recycled pyrite
0.61 g Ag/kg Cu, E = 450 mV, T = 80°C
Fresh pyrite
60
Galvanically-Assisted Leaching
PyriteChalcopyrite
FeS2
Cu2+
CuFeS2
S0 Fe2+
Fe3+
Schematic diagram of galvanically-assisted chalcopyrite leaching
Fe2+
e-
Resistivity of sulfur product layer
61
8.05 ± 0.15 × 1010 ΩcmSulfur without silver
1.06 ± 0.10 × 107 ΩcmSulfur with silver
ResistivitySample ID
Based on Ohm’s law and Faraday’s law and knowing the driving force
Maximum Resistivity: 1.11 × 107 Ωcm
62
Sulfur Resistivity
4
5
6
7
8
9
10
11
12
13
14
0 100 200 300 400 500 600 700 800 900 1000
Silver to Sulfur Ratio (ppm)
Lo
g (
ρ)
(Ω.c
m)
63
Enhanced pyrite with Ag and Hg
0%
20%
40%
60%
80%
100%
0 20 40 60 80 100 120 140 160Time (h)
Co
pp
er
Extr
acti
on
Pyrite pretreated with silver, Ag/Py = 100 ppm
Pyrite pretreated with mercury, Hg/Py = 600 ppm
Natural pyrite, No Ag added, No Hg added
64
GALVANOX™ Conclusions• An improvement to the Galvanox™ process has been
developed. As little as 60 mg of silver per kg of copper is sufficient to ensure complete copper extraction typically within 10 to 15 hours of leaching
• The acceleration of chalcopyrite leaching in this process is attributed to the galvanic interaction between pyrite and chalcopyrite
• Pyrite has a critical role in this process and it provides an additional surface for ferric reduction
• Silver has a critical role in this process:
– It decreases the resistivity of sulfur layer by the formation of dispersed silver sulfide particles
– It increases the catalytic properties of pyrite and the rate of ferric reduction increases on silver-enhanced pyrite
WHAT OF THE FUTURE?
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