Lecture 10: Biohydrometallurgy Of Copper – General Principles, Mechanisms And Microorganisms
NPTEL Web Course
Lecture 10
Biohydrometallurgy Of Copper – General Principles, Mechanisms
And Microorganisms
Keywords: Bioleaching Of Copper, Leaching Reactions, Leaching Bacteria
In lectures 10-12, bioleaching of copper ores and concentrates is critically analyzed with
respect to use of different microorganisms, possible mechanisms, heap and bioreactor
leaching [42-63].
Copper production is poised to reach to about 20mt by 2012. More than 20% of world copper is
now produced through hydro and biometallurgy. To meet the ever - increasing demand, all types
of ore resources including low grade ores, overburden and even wastes from mining operations
need be economically processed. Biohydrometallurgy holds great promise in the economical and
environment-friendly processing of such copper resources, besides treatment of copper
concentrates.
The most successful copper leach operations have been in the bioleaching of secondary copper
sulfides and copper oxides (chalcocite, covellite, oxides and oxidized ores).
However,
chalcopyrite is the most abundant and the most refractory copper mineral which is not readily
amenable to mesophilic biooxidation processes. However, efforts are being made to bioprocess
chalcopyrite ores and concentrates using high temperature thermophilic organisms.
For example, Straits resources tested chalcopyrite heap leaching with good results.
Titan
Resources, operated trial runs on mixed nickel sulfide-chalcopyrite heaps at Radio Hill. Mintek
along with Iranian copper industries company are undertaking large scale pilot tests on heap
bioleaching of chalcopyrite ores at the Sarcheshmeh mines in Iran.
1
Course Title: Metals Biotechnology
Course Co-ordinator: Prof. K. A. Natarajan, IISc Bangalore
Lecture 10: Biohydrometallurgy Of Copper – General Principles, Mechanisms And Microorganisms
NPTEL Web Course
Oxidative bioleaching of chalcopyrite involves role of ferric ions as an oxidant and formation of
elemental sulfur. Reactions are controlled by redox potentials. Insoluble reaction products such
as sulfur and jarosite compounds formed on chalcopyrite surfaces can affect dissolution rates.
Sulfide ore dumps and heaps present a complex microbial habitat and many of the indigenous
microorganisms participate in the bioleaching processes.
In table 10.1, a few of the important mesophilic and thermophilic organisms isolated from sulfide
deposits are listed, all of which could play a role in bioleaching of copper minerals.
Acidithiobacillus ferrooxidans is the most widely studied organism with respect to copper
bioleaching.
Leptospirillum ferriphilum were found to outgrow At.ferrooxidans in many
bioreactor operations. Predominant roles played by L.ferrooxidans and At.thiooxidans at high
acidic levels in copper bioleach environments have been reported.
Moderate and extreme
thermophiles also are significant, especially at higher temperatures (40-800C). At.caldus is the
dominant sulfur oxidizer in many bioreactor operations. Sulfolobus spp become significant at
temperatures higher than 600C. Microbial consortia participating in a bioleaching process (heaps
or bioreactors) is indeed very complex.
Major bioleaching reactions for chalcopyrite are given below:
CuFeS2 + 4Fe+++ + 5Fe++ + Cu++ + 2S0
CuFeS2 + 4H+ = Fe++ + Cu++ + 2H2S
2Fe++ + 2H+ + 0.5O2 = 2Fe+++ + H2O
2S + 3O2 + 2H2O = 2H2SO4
3Fe+++ + 2SO4-- + 6H2O + M+ = MFe3(SO4)2(OH)6 + 6H+
Where M = K+, Na+ or NH+4
2
Course Title: Metals Biotechnology
Course Co-ordinator: Prof. K. A. Natarajan, IISc Bangalore
Lecture 10: Biohydrometallurgy Of Copper – General Principles, Mechanisms And Microorganisms
NPTEL Web Course
Table 10.1: Some iron and sulfur oxidizing microorganisms
(adapted from Watling H.R, Hydrometallurgy, 84 (2006), 81-108)
Acidianus brierleyi
S- -
pH 1.5 – 2.5
Acidimicrobium
ferrooxidans
Mixotroph
Fe++ oxdn. and Fe+++
redn.
Moderate thermophile
pH 2
Acidiphilum spp
Obligate heterotroph
Mesophiles
Acidithiobacillus
ferrooxidans
S, S- -, Fe++
pH 2 - 4
Acidithiobacillus
thiooxidans
S, S- -
pH 0.5 -2
Acidithiobacillus caldus
Mixotroph
S, S- -
Moderate thermophile
pH 2 – 2.5
Ferrimicrobium
acidiphilium
Heterotroph
Fe++, S- -
Mesophile, pH 1 - 2
Ferroplasma acidophilum
Leptospirillum ferriphilum
Pyrite oxidation
Fe++
pH 1 - 2
Mesophiles, some thermo
– tolerant
Leptospirillum
thermoferrooxidans
Pyrite
pH 1 – 2
Leptospirillum
ferrooxidans
Fe++
Mesophile, pH 1 – 2
Sulfobacillus acidophilus
Fe(II) oxidation; Fe(III)
reduction, S- -
Moderate thermophile.
Sulfobacillus
thermosulfidooxidans
S
pH 1 – 2.5
Sulfolobus metallicus
Strict
chemolithoautotroph, S, S-
Hyperthermophile
-
Sulfolobus acidocaldarius
Heterotroph
Hyperthermophile
3
Course Title: Metals Biotechnology
Course Co-ordinator: Prof. K. A. Natarajan, IISc Bangalore
Lecture 10: Biohydrometallurgy Of Copper – General Principles, Mechanisms And Microorganisms
NPTEL Web Course
Factors influencing bacterial mineral oxidation are given below:
Physicochemical and
Temperature
microbiological parameters
pH
Redox potential
Oxygen
Carbon dioxide
Mass transfer
Nutrient availability
Ferric ion concentration
Pressure
Surface tension
Presence of inhibitors
Microbial diversity, population and activity
Metal tolerance and adaptation
Mineral properties
Mineral type, compositions, grain size and liberation
Particle size, area
Porosity
Hydrophobicity
Presence of secondary minerals
Bioleaching
Leaching mode (in situ, heap, dump or reactor leaching)
Pulp density.
Stirring rate (reactor)
Heap geometry (heap leaching)
4
Course Title: Metals Biotechnology
Course Co-ordinator: Prof. K. A. Natarajan, IISc Bangalore
Lecture 10: Biohydrometallurgy Of Copper – General Principles, Mechanisms And Microorganisms
NPTEL Web Course
Important parameters influencing bioleaching processes are given in table 10.2.
Table 10.2: Some parameters influencing copper bioleaching processes
Parameter
Particle size
Pulp density
Influence
Reasons
Leaching rate increase with decrease in
Higher surface area, better
particle size
mass transfer and oxidation
High grinding costs for finer particles
rate, Higher cell attachment.
Bioleaching rates decrease with increase
Mass transfer rates lower and
in pulp density.
abrasion effects high. Slurry
density and viscosity high
Agitation
Bioleaching rates increase at higher
Uniform mixing and higher
impeller speeds upto critical level-
suspension of slurries, better
decrease if agitation rates increase
mass transfer rates -
further- High power consumption.
Bacterial damage due to high
shear and particle attrition.
Aeration
Bioleaching rates increase with aeration
Better availability of O2 and
rates
CO2
Lower size of gas bubbles preferable.
High mass transfer.
High power consumption with enhanced
aeration rates and finer bubble sizes.
Residence
High leaching rates with lower residence Slow kinetics, Higher
time
times, - low productivity.
bacterial wash-out.
5
Course Title: Metals Biotechnology
Course Co-ordinator: Prof. K. A. Natarajan, IISc Bangalore
Lecture 10: Biohydrometallurgy Of Copper – General Principles, Mechanisms And Microorganisms
NPTEL Web Course
Leaching methods for hydrometallurgical extraction of copper are illustrated in table 10.3.
Table 10.3: Leaching methods for hydrometallurgical extraction of copper
Leach
Nature of ore
Grade
method
In situ
Dump
Heap
Percolation
Agitation
Vat
Approximate
Period
particle size
Oxide and
sulfides
Oxide /
sulfides-run
of mine and
lean ores
Oxide and
secondary
sulfides
Oxide
Oxide
concentrate
Roasted
0.2-0.5
0.2-0.5
200-400 mm
Typical
Cost
operation
4-20 years
2-15 years
4-5 million
tonnes
4-5 million
tonnes
-Low
0.2-0.5
100-250 mm
3-6 months
3x105 tonnes
Low
1-2
20-30
5-10 mm
< 0.1mm
5-10 days
2-6 h
5-15 vats
40-50 tanks
High
High
2-6 h
40-50
30-40
A diagrammatic analysis illustrating the beneficial effect of high temperature leaching of
chalcopyrite using thermophilic organisms (instead of acidophilic mesophiles) is given in
fig.10.1.
6
Course Title: Metals Biotechnology
Course Co-ordinator: Prof. K. A. Natarajan, IISc Bangalore
Lecture 10: Biohydrometallurgy Of Copper – General Principles, Mechanisms And Microorganisms
NPTEL Web Course
Fig. 10.1: Effect of temperature and thermophiles on copper dissolution
For copper oxides and secondary sulfides, direct heap or dump leaching can be used and the
efficiency of copper dissolution depends on the type of mineral and mineralogy.
Copper oxides require only a few hours, where as secondary sulfides such as chalcocite and
covellite take upto several months for acceptable copper recovery from heaps. On the otherhand,
chalcopyrite would require years of leaching since its leaching rate is only about one fifth rate of
chalcocite. Possible biooxidation reactions for various copper minerals are given in table.10.4.
7
Course Title: Metals Biotechnology
Course Co-ordinator: Prof. K. A. Natarajan, IISc Bangalore
Lecture 10: Biohydrometallurgy Of Copper – General Principles, Mechanisms And Microorganisms
NPTEL Web Course
Table 10.4: Dissolution reactions of some copper minerals in heaps and dumps
(Adapted from H.R.Watling, Hydrometallurgy, 84 (2006) 81-108)
Mineral
Reactions
Chrysocolla
CuSiO3 . 2H2O + 2H+ = Cu++ + SiO2 . 3H2O
Tenorite
CuO + H2SO4 = CuSO4 + H2O
Malachite
Cu2(CO3)(OH)2 + 2H2SO4 = 2CuSO4 + CO2 + 3H2O
Azurite
Cu3(CO3)2(OH)2 + 3H2SO4 = 3CuSO4 + 2CO2 + 4H2O
Native copper
Cu + 1/2O2 + H2SO4 = CuSO4 + H2O
Cuprite
Cu2O + 1/2O2 + 2H2SO4 = 2CuSO4 + 2H2O
Chalcocite
Cu2S + 1/2O2 + H2SO4 = CuS + CuSO4 + H2O
Cu2S + Fe2(SO4)3 = CuS + CuSO4 + 2FeSO4
Bornite
Cu5FeS4 + 2Fe2(SO4)3 = 2CuS + CuFeS2 + 2CuSO4 + 4FeSO4
Covellite
CuS + 2O2 = CuSO4
CuS + Fe2(SO4)3 = CuSO4 + 2FeSO4 + So
Enargite
Cu3AsS4 + 4 l/2Fe2(SO4)3 + 2H2O = 3CuSO4 + 9FeSO4 + 4So + HAsO2 +
11/2H2SO4
Chalcopyrite
CuFeS2 + O2 + 2H2SO4 = CuSO4 + FeSO4 + 2So + 2H2O
8
Course Title: Metals Biotechnology
Course Co-ordinator: Prof. K. A. Natarajan, IISc Bangalore