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High temperature heap leaching of chalcopyrite:

Method of evaluation and process model validation

Clement ChibwanaMetallurgist, Base Metals Technology-CPY Project 13th July 2012

BM Technology - CPY Project Team

Disclaimer

Slide 2

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Bioleaching process to increase rate of sulphide mineral leaching

Fe2+

Fe3+

Cu2+

H+

O2, CO2

diffusion through micro-poresair flow

migration or flow throughliquid film

reaction with mineral grains

absorption of oxygen & CO 2 into liquid film

solution phase solid phasegas phase

reaction with secondary sulphur

SO42-

BacterialGrowth

Bioleach Process: Catalytic effect enhancing oxidation rates of ferrous iron & sulphur by oxygen

- High solution Eh & fast leach kinetics

- Heat generation by oxidation of pyrite achieving high temperatures

solution flow

Slide 3Clement Chibwana, Metallurgist, Base Metals Technology –CPY Project, 13th July 2012

Development strategy to scale-up from laboratory to commercial heap

Slide 4

Accurate, reliable simulation

Validated computer model

Design Parameters for Commercial Scale Heap

Understand Microbial Ecology: Optimisation of Inoculation & Microbial Growth Rates

6m Columns

Simulation Columns

Clement Chibwana, Metallurgist, Base Metals Technology –CPY Project, 13th July 2012

Inoculation strategy to achieve microbial succession

Time

Tem

pera

ture

ChalcopyriteLeaching Zone

10 oC

45 oC

32 oC

68 oC

50 oC

25 oC

65 oC

Moderate

thermophiles

50 oC

High temperature

mesophiles

35 oC

Low temperature

mesophiles

Thermophiles

Sulfolobus metallicus

Metallosphaera sp.

Archaea JTC 1/2Ferroplasma JTC

Acidithiomicrobium & Acidimicrobium sp.

Acidithiobacillus caldus

Leptospirillum ferriphilum

Acidithiobacillus ferrooxidans

Acidithiobacillus thiooxidans

Sulfobacillus disulfidooxidans

Sulfobacillus MAD

60 oC


Simulation column construction


Simulation column operation: loading & unloading


Sulphide mineral distribution of the chalcopyrite o re showing copper source ratio’s (CSR)


Gangue mineral distribution of thechalcopyrite ore


Simulation column Pregnant Leach Solution (PLS) pH & Eh profiles

Slide 10

400

500

600

700

800

900

1000

1,0

1,5

2,0

2,5

3,0

0 50 100 150 200 250 300 350

Pot

entia

l vs

SH

E /m

V

pH

Leach Period /days

PLS pH PLS solution potential


Simulation column oxygen utilisation

Slide 11

0

10

20

30

40

50

60

70

0 50 100 150 200 250 300

% O

xyge

n U

tilis

ed

Time (days)


Simulation column mineral extraction and temperature profiles

Slide 12

0,0

1,0

2,0

3,0

4,0

5,0

6,0

7,0

8,0

9,0

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200 250 300

Air

and

Liqu

id fl

ow /

Kg.

m-2

.hr

Ave

rage

Tem

pera

ture

/°C

Pyr

ite O

xida

tion

/% C

oppe

r E

xtra

ctio

n /%

Leach Period /days

Average Temperature Pyrite Oxidation Copper Extraction Air flow Liquid flow


Microbial population change in solution as a function of ore temperature : simulation column

Clement Chibwana, Metallurgist, Base Metals Technology –CPY Project, 13th July 2012 Slide 13

Simulation column energy balance

Slide 14

0

10

20

30

40

50

60

70

80

-80

-60

-40

-20

0

20

40

60

80

100

0 50 100 150 200 250 300

Tem

pera

ture

(oC

)

Ene

rgy

per

unit

volu

me

(W

/m3)

Time (days)

Energy at Top Energy at Bottom Energy Accumulation Energy Generated Column Temperature


Simulation column temperature profile


Process model fit to extraction & temperature profi les of the simulation column

Slide 16

0

10

20

30

40

50

60

70

80

0

10

20

30

40

50

60

70

80

0 50 100 150 200 250 300

Ave

rage

Col

umn

Tem

pera

ture

(de

g C

)

Cop

per

Ext

ract

ion

(%

)

Leach Period (days)

Calculated Copper Extraction

Measured Copper Extraction

Calculated Average Temperature

Measured Average Temperature


Process model fit to oxygen utilisation

Slide 17

0

10

20

30

40

50

60

70

80

90

0 50 100 150 200 250 300

Oxy

gen

Util

isat

ion

(%

)

Leach Period (days)

Calculated Measured


Process model fit to net acid consumption results

Slide 18

-10

-8

-6

-4

-2

0

2

4

6

0 50 100 150 200 250 300

Net

Aci

d C

onsu

mpt

ion

(kg

/t)

Leach Period (days)

Calculated Measured


Progress since IBS 2007


Pilot heap : 500 000 kT Ore


Hot zones of heap 9-15m depth

S

1

4

23

6 5

789

N

S

EW


Pilot heap 3D temperature profiles

3 m 6 m 9 m

15 m 18 m

November 1 2007: 5 days irrigation to low flowrate (between 10 &14 m3/h)


November 30 2007: 34 days irrigation to rate 2l/h/m2

3 m 6 m 9 m

15 m 18 m



December 15 2007: 49 days irrigation to rate 4.5 l/h/m2

3 m 6 m 9 m

15 m 18 m



December 25 2007: 59 days irrigation to rate 5 l/h/m2

3 m 6 m 9 m

15 m 18 m



3 m 6 m 9 m

15 m 18 m

January 12 2008: 77 days irrigation to rate 5.5 l/h/m2



3 m 6 m 9 m

15 m 18 m

January 26 2008: 91 days irrigation to rate 5.5 l/h/m2


Clement Chibwana, Metallurgist, Base Metals Technology –CPY Project, 13th July 2012 Slide 27

February 12 2008: 108 days irrigation to rate 5.5 l/h/m2

3 m 6 m 9 m

15 m 18 m



February 20 2008: 116 days irrigation to rate 4.5 l/h/m2

3 m 6 m 9 m

15 m 18 m



March 12 2008: 137 days irrigation to rate 1.5 l/h/m2

3 m 6 m 9 m

15 m 18 m



March 20 2008: 145 days irrigation to rate 2 l/h/m2

3 m 6 m 9 m

15 m 18 m



April 3 2008: 159 days irrigation to rate 3 l/h/m2

3 m 6 m 9 m

15 m 18 m



April 22 2008: 178 days irrigation to rate 3 l/h/m2

3 m 6 m 9 m

15 m 18 m



May 10 2008: 196 days irrigation to rate 4.5 l/h/m2

3 m 6 m 9 m

15 m 18 m



May 25 2008: 212 days irrigation to rate 4.5 l/h/m2

3 m 6 m 9 m

15 m 18 m



Jun 5 2008: 222 days irrigation to rate 4.5 l/h/m2

3 m 6 m 9 m

15 m 18 m



Jun 22 2008: 239 days irrigation to rate 3 l/h/m2

3 m 6 m 9 m

15 m 18 m



July 15 2008: 262 days irrigation to rate 3 l/h/m2

3 m 6 m 9 m

15 m 18 m



July 27 2008: 274 days. Since July 22 cut irrigation and drainage starts

3 m 6 m 9 m

15 m 18 m



August 7 2008: 285 days. Continuous period of drainage

3 m 6 m 9 m

15 m 18 m



Mineral dissolution versus depth: Hot zone

AVG Recoveries in Hot and Cool Zones by Depth

0

10

20

30

40

50

60

70

80

90

100

Cc Cv Cp Bn CuT Pyrite

Rec

.%

HOT 0-6

HOT >6

COOL 0-6

COOL >6


Conclusions

The results presented demonstrate the ability of high temperature bioleaching to effectively leach a primarycopper ore. The copper recovery achieved was 75% in a leach cycle of 283 days.

The application of the Simulation Column patented by BHP Billiton - Base Metals (US Patent No. US 7727510B2, 1 June 2010) has been demonstrated, showing that self-generation of heat from bioleaching of pyritecontained in the ore may be managed to sustain high operating temperatures (average of 70 °C).

The success of bioleaching was attributed to the inoculation strategy and the ability to achieve microbialsuccession as the ore temperature increased.

The Process Model developed by BHP Billiton - Base Metals was validated against experimental results fromoperation of the Simulation Column.

The High Temperature Heap Leach Process has been tested in a 500 kT Pilot Heap confirming that highchalcopyrite dissolutions may be achieved at heap temperatures of >50°C.

The development work by BHP Billiton – Base Metals has laid the foundation for the application of HighTemperature Heap Leaching for treatment of suitable primary copper ores.

The gangue mineral composition, crush size, and ore permeability as a function of heap height and leach time,are also critical factors that determine the heap design and leach performance.


Acknowledgements

The high standard of work by the Mintek Biotechnology Division is acknowledged along with significant

individual contributions by Stefan Robertson (Mintek) and Heinrich Muller (Mintek), which combined to make

the test program a success.

The support work by the University of Cape Town is recognised, in particular the work carried out by Nathan

van Wyk for the molecular biology work done on the samples.

Acknowledgement is also given to Hatch Africa (Pty) Ltd and Wade Walker for the design and construction of

the columns described in this paper and for their engineering support during the operation of the column.


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