Bioleaching technology - mine waste management - chemolithotrophic bacterias

1. Sulphide mineral leaching
chemistry of sulphide
oxidation of bacteria

2. Content
● Introduction
● Microorganisms
● Bioleaching processes
● Conclusion
● Bibliography

3. Introduction
1. Metals as minerals are present as oxides, carbonates or sulphides in
the earth’s crust
2. Minerals in which metals are concentrated are called ‘ores’
3. Conventional methods for metal recovery - pyrometallurgy,
hydrometallurgy and pyrohydrometallurgy
4. Mine wastes - pyrite - common sulphide ore - oxidation - Acid Mine
Drainage (AMD) - serious problem

4. 166 AD
First time in copper
mine at Cyprus -
copper recovery
Commercial
scale
Rio Tinto mine at
Spain Copper heap
leaching
Colmer
and Hinkle
First to demonstrate
bacterial catalysis of
iron oxidation
Isolated the bacterial
strain T. ferrooxidans
1920
Reported the oxidation
of Zinc sulphide by
Sulphur oxidisers
Not confirmed till 1947
Then came
Biometallurgy
Biohydrometallurgy
Bioleachinig

5. Bioleaching
Water insoluble metal sulphide Water soluble metal sulphates
A branch of biohydrometallurgy
Ability of microorganisms or their metabolites to attack or dissolve metals

6. Microorganisms
● Backbone of biomining activity
● Isolated from industrial
leaching operations
● Includes bacteria, fungi,
archaea, alage, and some
yeast
● Rio tinto – ‘copper mine’ - first
large scale operation to isolate
organisms for leaching
● Colmer and Hinkle isolated the
strain - Thiobacillus

7. Diverse group of
bacteria
Chemolithotrophs - use ferrous ions and
reduced sulphur compounds for energy
source
Important mesophiles are:
Acidothiobacillus ferrooxidans
Acidothiobacillus thiooxidans
Leptospirillum ferrooxidans,
Chromebacterium violaceum, Micrococcus
lactilytious, Methallogenium spp.,
Hyphomicrobium spp., Desulfovibrio spp.
Desulfotomaculum spp
Moderate and extreme thermophiles
Sulfolobus spp. TH-1, Acidinus spp.,
Acidiphilum spp, Acidimicrobium
ferrooxidans, Thiobacillus caldus ,
Galolieria sulphararia , Sulfobacillus
thermosulfidooxidans, Ferromicrobium
spp., Metallosphera and Sulfurisphaera

8. Microorganisms involved in bioleaching and
their preferred energy source
Energy source used by the organism
Ferrous iron
Elemental sulphur
Microorganism
Acidithiobacillus ferrooxidans
Leptospirillum spp.
Ferroplasma acidarmanus
Acidimicrobium ferrooxidans
Ferromicrobium acidophilus
Alicydobacillus tolerans
Sulfolobus metallicus
Metallosphaera spp.
Acidianus spp.
Sulfobacillus acidophilus
Acidithiobacillus thiooxidans
Acidithiobacillus caldus

9. Mechanisms

10. Mechanisms of bioleaching
Metal extraction from the sulphidic ores,
concentrate and tailing was initially
described by two mechanisms
1. Direct leaching or enzymatic
oxidation
2. Indirect leaching or non -
enzymatic oxidation
3. Galvanic conversion
 Ferric ion - Oxidising agent
 Ferric ion and proton (+) ion is
responsible for mineral solubilization
 Microorganisms - produce chemical
agents - ‘LIXIVIENT’ - and produce
space for leaching reaction to take
place - ‘EXOPOLYSACCHARIDE’ serves
as space

11. The mineral dissolution reaction
is not identical for all metal
sulphides as it varies depending
on the nature of the sulphides.
The oxidation of different metal
sulphides proceeds by means of
one of the two main pathways
via different intermediates.
Pathways
1. Direct
2. Indirect
3. Thiosulphate pathway
4. Polysulfide mechanism

12. Direct/contact
Bacteria in physical
contact with the
mineral surface and
resulting in the
oxidation of iron
sulfides

13. Indirect mechanism
No physical contact is here necessary
Bacteria lixiviant
Acid and/or iron(III) - oxidizing agents
Bacteria - catalyst of the mineral dissolution,
concentrating the attacking agents (i.e., protons
and/or iron(III) ions) at the interface of the minerals
and thus enhancing the degradation process
Iron(II), elemental sulphur, sulphates, thiosulphates,
and hydrogen sulphide are produced

14. Recent studies - redefined pathways
Acid solubility of the minerals

15. Thiosulphate pathway
Occurs when the acid insoluble metal sulphides
such as pyrite (FeS2) and molybdenite (MoS2) are
oxidized
Solubilisation - ferric iron attack on the acid-
insoluble metal sulphides where thiosulfate is the
main or first intermediate and sulphate is the main
end product

16. Polysulfide mechanism
Takes place when the acid soluble metal sulphides such as sphalerite (ZnS),
chalcopyrite (CuFeS2) or galena (PbS) are solubilised
In this case, solubilisation - combined attack by ferric iron and protons, with
elemental sulphur as the main intermediate
Elemental sulphur is relatively stable but may be oxidized to sulphate by the
sulphur-oxidizing microbes present in the system

17. In both the pathways, the ferrous iron
produced gets re-oxidized to ferric iron
by the iron-oxidizing microorganisms
EPS layers, which provides a zone of high oxidation activity

18. Factors
Nutrients
O2 and CO2
pH
Temperature
Mineral substrate
Heavy metals
Surfactants and organic extractants
Redox potential
Influencing bioleaching

19. Conclusion
Further scope
● Low cost carriers - Organic
carriers can be used for
immobilization
● Designing a well controlled
reactor system – to minimize the
release of GMM in environment
● Prolong the life of immobilized
carriers and increase the biomass
concentration

20. Thank you