Analysis of biological and metallurgical factors which can control copper leaching

rate in bioleaching operations

Toms Vargas

Center of Hydrometallurgy/Electrometallurgy/Biohydrometallurgy

University of Chile

Bioleaching of copper sulfides in dumps and heaps is to day a well established technology. First dump leaching operations: Rio Tinto, Spain; Cananea, Mexico (60-70s)The first plant to bioleach secondary copper sulfides in heaps was built in Lo Aguirre, near Santiago, in 1990 (approx) with the technology developped by the R&D group of Minera Pudahuel, a Chilean company. Today Chile concentrates more that 50% of world copper produced with this technology (J.Brierley, IBS 2011)

PLANTA TRES VALLES, 30.000 TON CU CATHODES, VALE (2010)

BacteriaCu+2

Fe+2Fe+3

CuS

LIXIVIACIN BACTERIANA EN PILASBIOLEACHING OF COPPER SULFIDES

with permission of VALE S.A:

However, there are too many expectations about the impact of the addition of inocula or the improvement of oxidative capacity of microorganisms (by genetics or adaptation), on the rate of copper leaching

Leaching time

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(

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100

Abiotic system+ bact ++ bact +++ bact

THERE IS A CONSTANT SEARCH FOR FASTER LEACHING RATES AND BETTER COPPER RECOVERIES

When inoculation or improvement of bacterial activity could be of any benefit?:

It would be of any benefit only in conditions in which the rate of dissolution of the sulfide is limited by the oxidative activity of microorganisms

To define this is not a microbiological problem: it demands a global view of the process, pondering simultaneously biological and metallurgical factors.

Fe+3 + e- Fe+2

O2 + 4H+ + 4e- 2H2O

Cu+2 + S0 + 2e CuS

+ 1.229

+ 0.77

+ 0.55

e-

e-

Flow of electrons in dissolution of sulfides under bacterial catalytic action

bacteria

42

22

ln4

229.1 +++= HOOHOcp

FRTE

SOME FUNDAMENTAL ASPECTS

Fe+3

Fe+2

H+, O2

H2O

CuxS

e-

O2 , CO2(Solution)

Electron transport in the bioleaching of sulfides in the presence of Fe+2, Fe+3 ions

T.f.

Cu+2

THE CORE REACTIONS

H2SO4

Air:O2, CO2

CuOxCu4(OH)6SO4

FeOx Fe3+

Fe2+

Clays

Q

Cu 2+

Gangue

H2SO4

S0 Cu2SCuS,CuFeS2Cu5FeS4FeS2

Fe3+

At.f.T.f.

At.f.Lept.f

Fe3+

Fe2+

Cu2+

Clays

Fe2+

H2O

(Q)

Jarosites

H2OH

A FULL PICTURE IS NECESSARY

Fe+2, H+, O2

Fe+3 Fe+3

Fe+2

SULFIDE

BACTERIA

H+

O2

Fe+3 + MS Fe+2 + Cu+2 + S0

4Fe+2 + O2 + 4H+ 4Fe+3 + 2H2OA SIMPLIFIED BUT USEFUL SCHEME

Fe+2, H+, O2

Fe+3 Fe+3

Fe+2

SULFIDE

BACTERIA

H+

O2

CASES WHERE INOCULATION WOULD NOT BE OF ANY ADVANTAGE: A: CONTROL BY ACID SUPPLY

BIOLEACHING OF EL TENIENTE CRATER: A CASE CONTROLLED BY ACID SUPPLY

EFFECT OF ACID CONCENTRATION IN FEEDING SOLUTION

Time, weeks

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OXIDATIVE POTENTIAL IN EXIT SOLUTION

Time, weeks

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MICROORGANISMS IN EXIT SOLUTION

Time, weeks

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COPPER IN EXIT SOLUTION

SYSTEM CONTROLLED BY ACID SUPPLY: INOCULATION WOULD NOT BE OF ANY BENEFIT IN THIS CASE

CONTROL BY H+

DIFFUSION IN HEAPS

(Petersen and Dixon, 2003)Leaching time

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Long dripper spacing

Short dripper spacing

H+

Fe+2, H+, O2

Fe+3 Fe+3

Fe+2

SULFIDE

BACTERIA

H+

O2

CASES WHERE INOCULATION WOULD NOT BE OF ANY ADVANTAGE: B: CONTROL BY OXYGEN SUPPLY

e- e-

O2, H+

Fe2+

Fe3+

CuS

2 m

O2

Fe3+ Fe2+

Fe3+ + CuxS Fe2+ + S0 + x Cu2+

H2O

COPPER BIOLEACHING IN HEAPS WITH AIREATION BY NATURAL CONVECTION: A CASE OF CONTROL BY OXYGEN SUPPLY

R. Montealegre et al. (1995), Copper 95, Santiago, Chile

EFFECT OF FORCED AIREATION

T. Lancaster and D. Walsh (1997), IBS-1997, Melbourne, Australia.

G= 1.7 [L/m^2-min]

0123456

0 5 10 15 20 25

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G= 4.2[L/m^2-min]

0

2

4

60 5 10 15 20 25

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G= 6.5[L/m^2-min]

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60 5 10 15 20 25

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Oxygen profiles as a function of heap height at three aeration rates. H.M. Lizama. Int. J. Miner. Process. 62 (2001) 257269

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oxygen in air (OA), %

EFFECT OF AIR FLOW ON THE INCREASE OF COPPER RECOVERY OVER THE BASAL CASE OF NATURAL AIREATION

H. Salomon (2000), Learned lessons in high altitude leaching, Expomin, May 2000, Santiago, Chile

O2 , CO2

CLUSTERS OF PARTICLES IN STAGNANT SOLUTION ZONES

HOWEVER, OVER CRITICAL AIR FLOW (~10 L/min m2) SYSTEM CAN STILL BE CONTROLLED BY SUPPLY OF OXYGEN OR CO2 TO REACTION ZONE

Fe+2, H+, O2

Fe+3 Fe+3

Fe+2

SULFIDE

BACTERIA

H+

O2

CASES WHERE INOCULATION COULD BE OF ANY ADVANTAGE: GOOD SUPPLY OF ACID, OXYGEN AND, CO2

Fe+2, H+, O2

Fe+3 Fe+3

Fe+2

SULFIDE

BACTERIA

M+n

[MS]

(X)

][][

*1 232

+

+

+

= +

FeFeK

Xvv Max

Fe

[ ]][][1 3

2

max

2

+

++

+

==+

FeFeB

MSvbvv MSMSMSFe

Rate of Fe+2 consumption by bacterial oxidation (-v) and rate of chemical leaching of MS, expressed as rate of Fe+2 generation by reduction of Fe+3 during leaching of MS (+v), expressed as a function of Eh.

0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9Solution Eh, V(SHE)

X4X3X2X1

-vFe+2, bact +vFe+2, chem

0MS

3MS

2MS

1MS

[ ]][][1 3

2

max

2

+

++

+

==+

FeFeB

MSvbvv MSMSMSFe

][][

*1 232

+

+

+

= +

FeFeK

Xvv Max

Fe

MS(t) X(t)

0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9Solution Eh, V(SHE)

X4X3X2X1

-vFe+2, bact +vFe+2, chem

0MS

3MS

2MS

1MS

SMALL N MICROORGANISMS HIGH REACTIVITY OF MS: INOCULATION HAS A IMPACT

LARGER N MICROORGANISMS SMALLER REACTIVITY OF MS: INCULATION DOES NOT HAVE AN IMPACT

THE RATE OF COPPER SULFIDE LEACHING IS CONTROLLED BY BACTERIAL ACTIVITY WHEN Vmax X < VMSmax . AFTER THAT BACTERIAL INOCULATION IS OF NO USE

AN APPLICATION:EVOLUTION OF COPPER, PLANCTONIK BACTERIA, Eh AND pH DURING BIOLEACHING OF A COPPER CONCENTRATE WITH A. ferrooxidans

From: J. Casas (1991), M.Sc. thesis in Chemical Engineering, University of Chile.

time, days

With adequate data on kinetics of +vFe+2 and vFe+2 it is possible to model the impact of bacterial population on copper sulfides bioleaching

bact. population

Fe+3

Cu+2L. Lufin, 2007

A CASE CONTROLLED BY MICROBIOLOGICAL ACTIVITY: BACTERIAL ACTIVITY INHIBITION DUE TO MISSMANAGEMENT OF SOLUTION CHEMISTRY :

Al2(SO4)3

MnSO4

H2SO4

CuSO4

Fe(SO4)x

H+

Cu2+

Al2(SO4)3

MnSO4

H2SO4

CuSO4

Fe(SO4)x

AlOx

MnOx

CuOx

FeOx

CaOx

CaSO4(ppt)

H2SO4LEACHING SOLVENT

EXTRACTION

SOLUTION REMAINING IN LEACHED ORE

JAROSITES PRECIPITATION, GYPSUM PRECIPITATION, ETC.

ORGANIC

C1 C2 C3

[ SO42-, Xi+]

max

BACTERIAL INHIBICION DUE TO HIGH IONIC CONCENTRATION

1.0

0

CONCLUSIONSImprovement of bacterial oxidative activity (X x max ) through inoculation (larger X) or by adaptation/genetic modification (larger max) could have any impact on copper leaching rate only if there is good supply of solution, H+ ,O2 and CO2 to reacting sites.Inoculation of the ore would be of any benefit only in conditions in which the rate of dissolution of the sulfide is limited by the oxidative activity of microorganisms. The impact of inoculation can be assessed in advanced in this case from kinetic data of biological ferrous iron oxidation and copper sulfide leaching, using modelling.Unless there are strong inhibitig conditions, the system will be rearly controlled by bacterial oxidative activity.Questionable to claim advantages for some particular microorganisms

Fe+2

Fe+3Fe+3(FeOX)

Cu+2

SO4-2S2-2

S0

CHALCOPYRITESUBPRODUCTS

LAYER SOLUTION

Cu+

Fe+3

CuOX

e Fe+3?

IDEAL SITUATION: COPPER LEACHING RATE CONTROLLED BY THE INTRINSIC RATE OF SULFIDE DISSOLUTION

THE QUESTION REMAINS: HOW MUCH CAN MICROORGANISMS DO TO HELP AT THAT LEVEL

CuFeS

??

?

?

?

DIRECT CATALYTICAL ACTION PREVENTED BY PHYSICAL CONSTRAINTS

THANK YOU