David Dreisinger Presentation - Peru October 2012 - Reduced

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.


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.


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.


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


____________________________________________

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


Overall Process

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%

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Time (h)

Cu

Re

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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)

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Cu

Re

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Galvanox Leaching

No Pyrite


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Time (h)

Cu

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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)

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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

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Unassisted chalcopyrite leaching

Potential set point = 470 mV (vs. Ag/AgCl), T = 80°C

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ComparisonSilver-enhanced pyrite additionNatural pyrite addition

Potential set point = 470 mV (vs. Ag/AgCl), T = 80°C

0%

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0 20 40 60 80 100

Time (h)

Co

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Pyrite #1, Py/Cp = 6

Pyrite #2, Py/Cp = 6

Pyrite #3, Py/Cp = 60%

20%

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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%

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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

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Recycled pyrite at low pulp density at different solution potentials

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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%

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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




10 g/L Cu concentrate, T = 80°C

Fresh pyrite Recycled pyrite

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High pulp density

0%

20%

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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

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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)

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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%

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100%

0 20 40 60 80 100

Time (h)

Co

pp

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Ex

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Py/Cp = 2, Ag/Py = 100 ppm, E = 450 mV

Same Silver Added, No Pyrite Added, E = 450 mV0%

20%

40%

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80%

100%

0 20 40 60 80 100

Time (h)C

op

per

Ex

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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

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Galvanically-Assisted Leaching

PyriteChalcopyrite

FeS2

Cu2+

CuFeS2

S0 Fe2+

Fe3+

Schematic diagram of galvanically-assisted chalcopyrite leaching

Fe2+

e-

Resistivity of sulfur product layer

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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

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Sulfur Resistivity

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5

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9

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13

14

0 100 200 300 400 500 600 700 800 900 1000

Silver to Sulfur Ratio (ppm)

Lo

g (

ρ)

(Ω.c

m)

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Enhanced pyrite with Ag and Hg

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100%

0 20 40 60 80 100 120 140 160Time (h)

Co

pp

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Extr

acti

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Pyrite pretreated with silver, Ag/Py = 100 ppm

Pyrite pretreated with mercury, Hg/Py = 600 ppm

Natural pyrite, No Ag added, No Hg added

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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?

David Dreisinger Presentation - Peru October 2012 - Reduced

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