1Lakefield Research

C.J. Ferron, C.A. Fleming, SGS Lakefield Research Limited

D. Dreisinger, University of British Columbia

T. O’Kane, O’Kane Consultants Inc.

Chloride as an Alternative toCyanide for the Extraction of

Gold - Going Full Circle?

2Lakefield Research

Outline

Introduction : A brief look at history

Chloride Process for Gold Extraction chloride and preg-robbers

PLATSOL for Cu-Ni-Au-PGM’s ores

treatment of Cu-Au concentrates

treatment of refractory Au concentrates (non-preg-robbers)

3Lakefield Research

Outline - continued

Gold Recovery from PLATSOL Liquor: - NaHS, Carbon, IX

Silver Recovery with PLATSOL

Gold Recovery from Preg-Robbing Ores

Engineering Implications

Conclusions

4Lakefield Research

Introduction - Flash-Back

Before cyanidation, chlorination was used Cl2 (gas), bleach + H2SO4, KMnO4 + NaCl + H2SO4

Cl2/HCl to dissolve Au (+PGM’s) in refineries

Putnam (1947)

Chloride roasting

Au-Sb slag in RSA

McGill University - Pressure chloride leaching with [Cl]

5Lakefield Research

PLATSOL DiscoveryAu, Chloride, Preg-Robbers

LIHIR

Santa Fe Pacific Gold Corporation

Con Mine

PLATSOL : add small amount of chloride to HTPOX (225oC) to dissolve Au + PGM’s

First Application : Northmet Project

6Lakefield Research

Eh - pH Diagram for the Au-Cl-H2O Systemat 25oC: [Au] = 0.00001M; [Cl] = 0.2M

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(-a)

7Lakefield Research

Effect of Chloride Additionson Metal Extractions

(225oC, 2 hours)

Effect of Temperature onMetal Dissolutions

(5g/L NaCl, 2 hours)

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20

g/L NaCl

% E

xtra

cti

on

Au

Pt

Pd

70

80

90

100

190 200 210 220 230 240

Temperature °C

% E

xtra

cti

on

Cu

Au

Pt

Pd

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Analyses of Various Cu-Ni Concentrates TestedElements Concentrate Type

% A B C D E F G H I _______________________________________________________Cu 2.1 12.0

Ni 0.9 9.9

Fe 12.6 35.9

S 7.3 34.1

Au g/t 2.5 3.6 4.0 12.4 5.0 0.9 0.5 3.0 2.1

Pt g/t 0.8 490

Pd g/t 2.0 294

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Results(10-20g/L NaCl; 220oC; 50g/L H2SO4 Initial; 100psi O2 overpressure)

% Concentrate TypeRec’y A B C D E F G H

Cu 99.9 98 99.9 99.9 99.9 99.3 99.0 99.3

Ni 99.9 99 99.9 99 99 93.8 99.6 98.7

Au 93 83 96 99 83 97.1 84.3 96.0

Pt 72 80 76 95 51 97.4 98.2 99.0

Pd 97 93 94 94 80 98.1 93.9 98.4

10Lakefield Research

PLATSOL forChalcopyrite-Au Concentrates

Origin Chile Canada Australia

Assays% Cu 28.9 32.0 26.1% S2- 29.6 28.5 29.3g/t Au 5.8 2.5 12

PLATSOL ConditionsT(ºC) 225 225 225g/L NaCl 10 10 10P80 (µm) 15 20 15Duration (h) 2 2 2

PLATSOL Results% Cu extracted 99.7 99.8 99.9% Au extracted 95.9 93.1 88.3

11Lakefield Research

PLATSOL for Refractory Gold Concentrates

Concentrate Origin South Africa South America Greece RomaniaType Au

encapsulatedin Fe2O3

Auencapsulated

in pyrite

Auencapsulated

in arsenopyrite

Auencapsulated

in arsenopyriteChemical Analysis

g/t Au 17.7 50.9 19.9 11.2g/t Ag 6.8 350 19.4 146

PLATSOL® Conditions

Temperature (ºC) 225 225 225 225Duration (h) 6 4 3 3

g/L NaCl 10 20 20 20P80 (µm) 25 16 15 16

PLATSOL® Results

Au extraction (%) 90 96 96 92Ag extraction (%) 41 5 99.5 7

12Lakefield Research

PLATSOL and Silver Concentrates

PRINCIPLE: PLATSOL

Silver Mineral AgCl in residue(and not Ag-Jarosite)

AgCl can be recovered from residuecyanidation flotationNaTS leaching

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PLATSOL and Silver Concentrates - continued

EXAMPLE 1: Ag-tetrahedrite, USA16% Cu, 30% Pb, 9.8% Sb, 3.5% AgPLATSOL = 99% Cu in solution, ~0% Ag

Cyanidation:95.4% (96 hours)NaTS: 87.5% (6 hours, RT)

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PLATSOL and Silver Concentrates - continued

EXAMPLE 2: Cu-Ag-Au-As concentrate from Peru

1.4% Ag, 21 g/t Au, 7% As

PLATSOL = Cu, Au (92.5%) in solution, ~0% Ag

ATS dissolved 88% Ag (one test)

15Lakefield Research

PLATSOL & Preg-RobbersFlotation of Graphitic Carbon

from PLATSOL Residue

AuFraction Wgt(%)

g/t % Recovery

Rougher 1 26.6 1132 75.4

Rougher 2 19.7 290 14.2

Total Rougher 46.3 774 89.6

Rougher Tail 53.7 77 10.4

PLATSOL®

Residue 100 399 100

16Lakefield Research

Gold Recovery fromPLATSOL Liquors

Various methods:

carbon

NaHS precipitation

ion exchange

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Extraction Isotherms at 45oC for Au, Pd from PLATSOL NorthMet Pulps.

AuRix 100 Resin

10

100

1000

10000

0.01 0.1 1

Concentration in Barren (mg/L)

Res

in L

oad

ing

(g

/t)

Au

Pd

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Engineering Implications1) Refractory gold autoclaves

(225oC, 100 psi O2, 20 - 40 g/L H2SO4)

2) Presence of 5 -10 g/L Cl Polymeric membrane

- Macraes- Laterites- Phelps Dodge

3) Rest of the circuit must handle acidic chloride solutions

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Engineering Implications- cont’d

But…

1) No cyanide circuit

2) Real potential for RIP, CIP

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CONCLUSIONS

Results indicate that the PLATSOL is a

viable non-cyanide alternative for:

copper-gold concentrates (i.e. Phelps Dodge) enargite-gold concentrates refractory non-preg robber ores/concentrates high silver concentrates (modified) especially

with Sb, As

21Lakefield Research

Adsorption of Metals from Autoclave Pregnant Leach Solution on Activated Carbon

Conditions Solution Assays (mg/L) Carbon Assays (g/t, %)Temp

ºC

Time

h

Carbon

g/LStream Au Pt Pd Au Pt Pd Cu Ni Fe

20 24 5 Preg 0.21 0.19 1.08Barren <0.01 0.03 0.07 14 31 197 0.72 0.54 0.18

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Elution of Activated Carbon-Zadra Method

ProductCarbon Analyses (g/t, %)

Au Pt Pd Cu Fe

Loaded carbon 16 118 732 0.15 0.20Eluted carbon 0.6 1.8 7 0.002 0.20

Elution efficiency % 96 98 99 99 ~0

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Extraction Isotherms at 45oC forAu, Pd from PLATSOL NorthMet Pulp

on Activated Carbon

10

100

1000

10000

0.01 0.1 1

Concentration in Barren (mg/L)

Car

bo

n L

oad

ing

(g

/t)

Au

Pd

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Kinetics of Gold CIP Adsorptionfrom NorthMet PLATSOL Pulp

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0 10 20 30

Time (h)

Res

idu

al A

u (

mg

/L)

85ºC

40ºC

25Lakefield Research

CIC Feed and Discharge Au Concentrations

Gold (mg/L)

Feed CIC-6 DischargePP5-1 0.10 0.01PP5-2 0.12 0.02PP5-3 0.08 <0.01PP5-4 0.09 0.01PP5-5 0.12 0.01PP5-6 0.14 <0.01PP5-7 0.11 <0.01PP5-8 0.08 0.01PP5-9 0.12 <0.01PP5-10 0.14 0.01PP5-11 0.10 <0.01PP5-12 0.13 <0.01PP5-13 0.11 <0.01

Average 0.11 <0.01

26Lakefield Research

Concentrations of Metals After Elution of Loaded Carbon

Metal Loaded Carbong/t

Eluted Carbong/t

ElutionEfficiency %

Au 88 2.7 97.2

Pt 107 5.3 95.2

Pd 454 18.3 96.0

Cu 2230 25 99.4

Ni 960 70 91.6

Fe 4200 4400 8