Microbial bioleaching uses microorganisms like bacteria and fungi to extract metals from low-grade ores in an economical way. Bacteria like Thiobacillus ferrooxidans and Thiobacillus thiooxidans produce acids that oxidize insoluble metals into soluble forms that can be extracted. Common metals extracted through bioleaching include copper, uranium, gold and nickel. Bioleaching offers advantages over traditional extraction methods by being lower cost, using less energy, and producing fewer emissions. It has been successfully commercialized to extract metals from mining waste and natural low-grade deposits.

1. Microbial Alchemy
(using bacteria to mine precious metals)
Speaker:
Shakshi Sharma
F-15-16-D

2. • Continuous depletion of Earth’s high-grade deposits of metals
necessitates the need for innovative and economical ways of
recovering metals from low-grade deposits.
• The necessity for utilisation of lean grade mineral resources
have become more urgent. Microbially-induced mineral
flotation and flocculation have been proved to very cost-
effective and environment-friendly.
• Ores with low metal content are not suitable for direct
smelting but it is possible to extract metals economically using
the activity of microorganisms.

3. Alchemy :
a seemingly magical
process of transformation,
creation or combination
Microbial Alchemy:
transforming metals from
something that has no
value into a solid,
precious metal that's
valuable,”
Biometallurgy:
has a good potential for
solving various
metallurgical problems
such as recovery of metal
from ores and minerals

4.  Microorganisms have been active in the
formation and decomposition of minerals
in the earth’s crust since life on earth
began.
 Our ability to harness the natural
capability of certain microbes to
decompose a variety of mineral deposits is
an old process that dates back to Roman
times in the first century BC.
History

5.  The first miners to exploit microbes, were probably the Romans some
2,000 years ago. They noticed that the fluid running off the mine tailings
was blue, an indication that it contained copper salts, from which they
then recovered the valuable metal.
 However, not until 40 years ago did it become clear that the copper in the
fluid was in fact the handiwork of a bacterium named Thiobacillus
ferrooxidans.
 Mankind has been using microbes for such activities without realizing that
these processes are mediated by microorganisms, but now with increasing
research trend in mineral biotechnology our interest toward the
phenomena has grown up and has given some potential results which
bring the revolution in mining industry.

6. As the world wides high grade ore reserves are falling out at an
appalling rate, because of high metal demand, traditional techniques
(pyrometallury, chemical processing) are becoming more and more
economically inviable.
Microbes bear a clear advantage over it as, not only they offer a
economically viable option but is also a clean technology. Microbes
converts metal compounds into their water soluble form.
By applying microbiological solublization process, it is possible to
recover metal values from industrial wastes. Majority of microorganisms
can interact with metals.

7. Bioleaching
Biomining
How to extract metals??

8. • Biological methods are:
 more cost-effective
 use less energy
 can function well at low concentration of
metals
 do not usually produce harmful emissions
 reduce the pollution of metal-containing
wastes
 Successful commercial metal-leaching
processes include the extraction of gold,
copper, and uranium.
The extraction of metals using mechanical and chemical methods is difficult
and expensive.

9. Microorganisms are used because they can:
 cause less environmental pollution in comparison to the traditional
leaching methods.
 very efficiently extract metals when their concentration in the ore
is low.
Microbial ore leaching (bioleaching) is
the process of extracting metals from
ores with the use of microorganisms.
This method is used to recover many
different precious metals like copper,
lead, zinc, gold, silver, and nickel.
Bioleaching

10. A bioleaching process takes place in a three phase
system:
Aqueous
phase:
is a solution of
salts providing
nutrients for the
microflora;
Gaseous phase:
consisting of
atmospheric
oxygen and
carbon dioxide.
Solid phase:
composed of the
finely ground ore
containing a mixture
of minor amounts of
waste rock and
metal values
combined with sulfur
to form metal
sulfides

11. Microorganisms Involved:
• Bioleaching used billion of rock cutting bacteria acting as a
catalyst to extract different metals. The most important
mineral-decomposing microorganisms are the iron- and
sulphur-oxidizing chemolithotrophs
• Metal-leaching microorganisms use ferrous iron and reduced
sulphur compounds as electron donors and fix carbon dioxide.
• Many of these microorganisms produce sulphuric acid
(acidophiles).

12.  The most commonly used microorganisms for bioleaching are:
• Thiobacillus ferrooxidans and
• Thiobacillus thiooxidans.
 Thiobacillus ferrooxidans is a rod-shaped, motile, non-spore
forming, gram-negative bacterium. It derives energy, from the
oxidation of iron or sulfur. This bacterium is capable of
oxidising ferrous iron (Fe2+) to ferric form (Fe3+), and
converting sulfur to sulfate (SO2-
4).

13. Thiobacillus thiooxidans
Thiobacillus ferrioxidans
Fig: Electron micrograph of bacteria

14. • Thiobacillus thiooxidans is comparable with T. ferrooxidams,
and grows mostly on sulfur compounds.
• Several studies indicate that the two bacteria T. ferrooxidans
and T. thiooxidans, when put together, work synergistically
and improve the extraction of metals from the ores.
• Besides the above two bacteria, there are other
microorganisms involved in the process of bioleaching:
 Sulfolobus acidocaldarius and
 S. brierlevi

15. Organism pH Temperature
0 C
Thiobacillus ferroxidans 2.5 30
Leptospirillum ferroxidans 1-2 45
Sulfobacillus acidophilus - 50
Sulfurococcus yellowstonii - 60-75
Leptospirillum ferroxidans 2.5-3.0 30
Sulfolobus solfataricus - 55-85
Sulfolobus rivotincti 2.0 69
Acidianus brierleyi 1.5-3.0 45-75
Acidianus infernus 1.5-3.0 45-75
Table : Optimum pH & temperature conditions for different organisms

16. A combination of two bacteria Leptospirillum
ferrooxidans and Thiobacillus organoparpus can
effectively degrade pyrite (FeS2) and chalcopyrite
(CuFeS2). The individual organisms alone are of no use in
extracting metals.
Pseudomonas aeruginosa can be employed in mining low
grade uranium ore. Another organism, Rhizopus arrhizus
is also effective for extracting uranium from waste water.
Certain fungi have also found use in bioleaching. Thus,
Aspergillus niger can extract copper and nickel while
Aspergillus oryzae is used for extracting gold. The
utilization of many of the other organisms is still at the
experimental stage.

17. Fig: Flow diagram of microbial bioleching

18. Fig: Extraction of Copper

19. Bioleaching technology
It has been shown that micro-organisms can
extract cobalt, nickel, cadmium, antimony, zinc,
lead, gallium, indium, manganese, copper, and
tin from sulphur-based ores.
The basis of microbial extraction is that the
metal sulphides, the principal component in
many ores, are not soluble but when oxidized to
sulphate become soluble so that the metal salt
can be extracted.

20. • The general metal recovery process can be
represented by the following equation:
MS + 2O2 MSO4
• It exerts its bioleaching action either directly or
indirectly
T. ferrioxidans

21. The bacteria which are naturally associated with the rocks
can lead to bioleaching by one of the following ways:
Direct action of bacteria on the
ore to extract metal.
Bacteria produce certain
substances such as sulfuric acid
and ferric iron which extract the
metal (Indirect action).

22. Direct
bioleaching:
Direct enzymatic attack
on the minerals by
microorganisms. Certain
bacteria (e.g., T.
ferrooxidans) can transfer
electrons (coupled with
ATP ) from iron or sulfur
to oxygen.
These organisms can
obtain energy from the
oxidation of Fe2+ to Fe3+or
from the oxidation of
sulfur to sulfate.
Indirect
bioleaching:
Bacteria produce strong
oxidizing agents ( ferric
iron and sulfuric acid)
helps in oxidation of
soluble iron or soluble
sulfur respectively.
Ferric iron or sulfuric
acid, being powerful
oxidizing agents react
with metals and extract
them.

23. Commercial process of bioleaching
 Commercial extraction of metal by bioleaching is
optimized by controlling the PH, temperature,
humidity, o2 and co2 concentrations.
These processes are:
 Slope leaching
 In-situ leaching
 Heap leaching

24. Slope leaching
1.)In slope leaching the
ore is finely ground and
kept in large pile in a
slope which is subjected
to continuous sprinkling
of aqueous solution of
microorganisms.
2.)The leach liquor
collected at the bottom
of the ore is processed
further for metal
recovery.
In situ leaching
1.) Ore is subjected to
bioleaching in its
natural occurrence,
aqueous solution of
microorganisms is
pumped through drilled
passages with in the
ore.
2.) The leach liquid
collected at the bottom
of the ore used for
metal extraction.
Heap leaching
3.) In heap leaching ore
is arranged in heap and
goes through the same
procedure as in slope
leaching. The aqueous
solution containing
microorganism works
on the heap of ore and
produces the leach
liquor.
2.)The leach liquor is
used for metal recovery.
Bioleaching approaches

25. Fig: Commercial bioleaching processes (A) Slope leaching (B)
Heap leaching (C) In situ leaching

26. Bioleaching plants
Copper bioleaching
plant
Heap bioleaching

27. Bioreactors
• The bioreactors used are the highly aerated stirred-tank designs
where finely ground ore is treated.
• Often nutrients such as ammonia and phosphate are added and the
bioreactor operated in a continuous manner.
The leaching can take days rather than the weeks required with dump
extraction, Ores such as chalcopyrite (CuFeS2) and energite
(Cu3AsS4) require temperatures as high as 75-80°C for leaching
which cannot be generated in dumps and therefore can only be
carried out in bioreactors

28. Main factors affecting bioleaching
Factors Effects
Physicochemical
1.) Temperature affects leaching rate, microbial composition and
activity (30-500C)
2.) pH needs to be low to obtain fastest leaching rates
and to keep ferric iron and metals in solution
(2.3-3.5)
3.) Oxygen reactions electron acceptor needed in chemical and
biological oxidation
Microbiological
1.) Microbial diversity culture
mixed cultures tend to be more robust and
efficient than pure
2.) Population density high population density tends to increase the
leaching rate
3.) Metal tolerance high metal concentrations may be toxic to
metals

29. • Copper ores (chalcopyrite, covellite and
chalcocite) are mostly composed of other
metals, besides copper. For instance,
chalcopyrite mainly contains 26%
copper, 26% iron, 33% sulfur and 2.5%
zinc.
• Bioleaching of copper ore (chalcopyrite)
is widely used in many countries. This is
carried out by the microorganism:
Thiobacillus ferrooxidans,
which oxidizes insoluble chalcopyrite
(CuFeS2) and converts it into soluble
copper sulfate (CuSO4).
Bioleaching of copper

30. • Copper leaching is usually carried out by heap and in situ
process. As the copper-containing solution (dissolved
state) comes out, copper can be precipitated and the water
is recycled.
• Extraction of copper by bioleaching is very common
since the technique is efficient, besides being economical.
• It is estimated that about 5% of the world’s copper
production is obtained via microbial leaching. In the USA
alone, at least 10% of the copper is produced by
bioleaching process.

31. Extraction mechanism
• Biomining of copper demands conversion of water-insoluble copper
sulfides to watersoluble copper sulfates. Copper ores such as
chalcocite (Cu2S) or covellite (CuS) are crushed, acidified with
sulfuric acid and agglomerated in rotating drums to bind fine
material to courser particles before piling in heaps. The heaps are
then irrigated with an iron-containing solution which percolates
through the heap and bacteria growing on the surface of the ore and
in solution catalyze the release of copper. The ferric iron generated
by the solution plays an important role in the production of copper
sulfate.
• Cu2S+2Fe(SO4)3 2CuSo4+4FeSO4+S
• CuS+Fe2(SO4)3 CuSo4+2FeSO4+S

32. • Bioleaching is the method of choice
for the large-scale production
uranium from its ores.
• Uranium bioleaching is widely used
in India, USA, Canada and several
other countries. It is possible to
recover uranium from low grade ores
(0.01 to 0.5% uranium) and low grade
nuclear wastes.
Bioleaching of Uranium:

33. • Bioleaching of uranium is an indirect process.
• Organism involved:
Thiobacillus ferrooxidans
• For optimal extraction of uranium by bioleaching, the ideal
conditions:
-Temperature: 45-50°C,
-pH: 1.5-3.5
• Heap leaching process is sometimes preferred instead of the in
situ technique. This is because the recovery of uranium in
much higher with heap leaching.

34. Bioleaching of gold
Generally gold is extracted by
treating with cyanide and then
gold from the cyanide extract is
treated with carbon.
The cyanide waste is a major
pollutant and has to be treated
before release into the environment.
Cyanide can be destroyed by a
sulphur dioxide or hydrogen
peroxide mixture.
However, there are biological
methods, both aerobic and
anaerobic, for the treatment of
cyanide.

35. • Micro-organisms known to oxidize cyanide
include species of the genera Arthobacter,
Bacillus, Micrococcus, Neisseria,
Thiobacillus, and Pseudomonas.
• Some ores are resistant to cyanide treatment
as the gold is enmeshed in pyrite (FeS2) and
arsenopyrite (FeAsS) and only 50% of the
gold can be extracted.
• The leaching is carried out in a sequence of
bioreactors with the first step bioleaching
the FeS2 and FeAsS so that the gold can
subsequently be extracted.

36. Extraction mechanism
• Gold is usually recovered from ores by solubilisation with a cyanide
solution and recovery of metal from the solution. In ores known as
refractory, small particles of gold are covered by insoluble sulfides.
The bacteria partially oxidize the sulfide coating. In the first stage,
bacteria catalyse the breakdown of the mineral arsenopyrite (FeAsS)
by oxidising the sulfur and metal (in this case arsenic ions) to higher
oxidation states while reducing dioxygen. This allows the soluble
products to dissolve.
• This process occurs at the cell membrane of the bacteria. The
electrons pass into the cells and are used in biochemical processes to
produce energy for the bacteria to reduce oxygen molecules to
water.
• In second stage, bacteria then oxidise Fe2+ Fe3+
• They then oxidise the metal to a higher positive oxidation state.

37. • The gold is now separated from the ore and in the solution.
Gold recovery from refractory minerals can increase from 15-
30% to 85-95% after biooxidation.

38. Bioleaching technique is also used for
extraction of other metals such as nickel, silver,
cobalt, molybdenum and antimony.
Bioleaching is useful for the removal of certain
impurities from the metal rich ores. For
instance, the microorganisms such as:
Rhizobium sp and
Brady rhizobium sp
Bioleaching of other metals

39. Advantages
of
Bioleaching
recover metals from
low grade ores in a
cost-effective
manner.
used to produce
refined and expensive
metals which
otherwise may not be
possible.
simple process with low
cost technology. It is
ideally suited for the
developing countries.
successfully
employed for
concentrating metals
from wastes or dilute
mixtures.

40. Time consuming(takes about 6-24 months or
longer)
Requires a large open area for treatment
Inconsistent yield because bacteria cannot
grow uniformly
High risk of contamination
Have a very low yield of mineral
Disadvantages of
Bioleaching

41.  Biomining is the extraction of
specific metals from their ores
through biological means usually
bacteria.
Microbial recovery of metals is
sometimes called “microbial
mining” or “biohydrometallurgy”.
Biomining occupies an
increasingly important place among
the available mining technologies.
Biomining

42. Mining mechanism
• Microorganisms involved in biomining gain
energy by breaking down minerals into
their constituent elements. The mineral
dissolution reaction is not identical for all
metal sulfides.
• Sand and coworkers (1999), have observed
that the oxidation of different metal
sulfides proceeds via Thiobacillus
ferrooxidans. They proposed two
mechanisms:
1.) Thiosulfate mechanism
2.)Polysulfide mechanism

43. For oxidation of acid insoluble metal
sulfides such as pyrite and molybdenite. In
this solublization is through ferric iron
attack on acid insoluble metal sulfides
For acid soluble metal sulfides such as
chalcopyrite, galena. In this solublization of
acid soluble metal sulfide through
combined attack by ferric ions and protons
Thiosulfate
mechanism
Polysulfide
Mechanism

44. • Today biomining is no longer a promising technology but an
actual economical alternative for treating specific mineral ores.
• Traditional extractions involve many expensive steps such as
roasting and smelting, which requires sufficient concentrations
of elements in ores while low concentrations are not a problem
for bacteria because they simply ignore the waste which
surrounds the metals, attaining extraction yields of over 90%
in some cases.

45. Bio Sorption:
Bio sorption primarily deals with the microbial cell surface
adsorption of metals from the mine wastes or dilute mixtures.
The microorganisms can be used as bio sorbents or bio
accumulators of metals. The process of bio sorption performs
two important functions:-
Both the above processes are concerned with a reduction in
environmental poisoning/pollution.
1. Removal of toxic metals from the industrial effluents.
2. Recovery of valuable but toxic metals.

46. Table: Microorganisms identified for biosorption of
toxic metals
Organism used Type Name of toxic metals
removed
Bacillus sphaericus Bacteria Chromium
Myxococcus xanthus Bacteria Uranium
Pseudomonas aeruginosa Bacteria Cadmium, Uranium
Streptoverticillium
cinnamoneum
Bacteria Lead
Rhizopus arrhizus Fungus Uranium
Saccharomyces cerevisiae Fungus Cadmium
(Source: Hu et al., 1996; Atkinson et al., 1998; Ahalya et al., 2003)

47. Fig : Microbial process

48. Bacteria:
Several bacteria and actinomycetes adsorb
and accumulate metals such as mercury,
cadmium, lead, zinc, nickel, cobalt and
uranium. For example:
Rhodospirullum sp can accumulate Cd,
Pb and Hg.
Bacillus circulans can adsorb metals such
as Cu, Cd, Co, and Zn
Rhodospirillum
Different group of microorganisms used in bio sorption process:

49. • There is a large scale production of fungal biomass in
many fermentation industries. This biomass can be
utilized for metal bio sorption from industrial effluents.
• Immobilized fungal biomass is more effective in bio
sorption due to increased density, mechanical strength
and resistance to chemical environment.
• Rhizopus arrhizus can adsorb several metallic cations
e.g. uranium, thorium.
• Pencillium lapidorum, P. spimuiosum are useful for the
bio sorption of metals such as Hg, Zn, Pb, Cu.
• Edible mushrooms were also found to adsorb certain
metals. For instance, fruit bodies of Agaricus bisporus
can take up mercury.
Fungi

50. • Several species of algae (fresh water
or marine) can serve as bio
accumulators of metals.
• For example:
• Chlorella vulgaris and C. regularis
can accumulate certain metals like
Pb, Hg, Cu, Mo and U. The green
algae Hydrodictyon reticulatum
adsorbs and accumulates high
quantities of Pb, Fe and Mn.
Algae

51. The need for biomining and bioleaching!!
Biomining will become more important as high-grade surface
mineral deposits are worked out and become less viable, and
mining companies will be forced to find other mineral sources.
These will include the working of low-grade ore deposits, mine
tailings, mine dumps, and worked-out mines.
It is a biological methods can function well at low concentration of metals,
do not usually produce harmful emissions and reduce the pollution of
metal-containing wastes.

52. Case studies
 Alan Goldstein and Robert Rogers, California State University in Los
Angeles (2015):
Phosphates have traditionally been extracted from ores either by burning them at
high temperatures to yield solid phosphorus or by treating them with sulphuric
acid to produce phosphoric acid. They evolved a pair of bacterial
strains, Pseudomonas cepacia E-37 and Erwinia herbicola, which can remove the
phosphate from the ore at room temperatures, without using corrosive sulphuric
acid.
Hindustan Copper Ltd (Kolkata) April 17, 2016:
contemplates using a cluster of bacteria to recover copper from its low grade
sulphide (chalcopyrite) ore by using state-of-the-art bio-leaching technique.

53.  Kashefi and Brown, 2016: researchers at
Michigan State University, uses the
bacteria Cupriavidus metallidurans to turn gold
chlroride—a toxic chemical liquid found in
nature—into 99.9% pure gold. It would be cost
prohibitive to reproduce their experiment on a
larger scale.
D B Nakeb, 2012: Biomining of copper using Halophilic Thiobacillus ferroxidans N
9.11 different bacterial isolates were isolated from hyper saline soil of kohlapur district. All
the isolates were investigated for bioleaching of copper using low grade chalcopyrite. Of all
the isolates, isolate no N-9 identified as Thiobacillus ferroxidans is found to be most
suitable for bioleaching of copper ore in both shake flask as well as bioreactor study. The
results showed that in the shake flask the isolate no.N-9 tolerates 40 g/L of Chalcopyrite
when supplemented with 0.5 G/L of yeast extract. 78% of copper can be extracted from 40
g/L of Chalcopyrite after 14 days.
Fig: gold flakes obtained
during experiment

54. Future Prospects
Scientist called biomining the "mining of the future".
Indeed, it is much cheaper and greener than traditional mining - there are a
lot fewer CO2 emissions
Furthermore, the toxic chemicals used in traditional mining can be
extremely harmful to the environment; there have been accidents before. In
case of biomining, the bacteria are naturally occurring at mining sites
anyway, and are not pathogenic.
Biomining is already in use in several countries, including South Africa,
Brazil and Australia.

55.  Overall, some 20% of the world's copper production comes
from bioleaching. The practice is not limited to copper.
Microorganisms are also used to extract gold and uranium.
And there are other applications of biomining: scientists are
working on using microbes to clean up the corrosive acid
pollution left over in mining waste.
 Scientists are now trying to genetically engineer new bacterial
strains that can stand up to toxic metals such as mercury and
cadmium.

56. In India, biomining and bioleaching has a great national
significance, where there is vast unexploited mineral potential .
The application of microorganisms for ore processing and waste
remediation is likely to become increasingly important in Indian
context in the coming years.
The bioleaching technology of silica magnesite by using Bacillus
Licheniformis developed at The Bose Institute, Calcutta, India is
being used for the first time in collaboration with the Department of
Biotechnology, Govt. of India.
Status in India

57. • Following are the industries which carry out biomining and
bioleaching in India:
 Hindustan Copper Limited (New Delhi)
 Bioleaching plants:
1.) The Bruhat Bangalore Mahanagara Palike (BBMP)
2.) GHMC (Greater Hyderabad Municipal Corporation)
 Uranium processing plant, Jaduguda (Jharkhand)

58. Conclusions
• The recovery of metals from mechanical and chemical methods is difficult to
carry out. To overcome this, certain biological methods are used nowadays.
These methods are useful for recovery of essential metals.
• The contribution of bioleaching is estimated to be approximately 15, 13 and
25% of the total world production of copper, uranium and gold.
• The use of acidophilic, chemolithotrophic iron- and sulfur-oxidizing microbes
mainly mesophiles in biological processes to recover metals are well
established.
• At present, bioleaching is being used commercially only for the recovery of
copper, uranium and gold. In future, however, these processes will become
important for several other metals such as zinc, nickel, cobalt and molybdenum
not only for extraction but also for environmental clean-up.
• Although biomining provides the possibility of recovering metals from many
low-grade deposits that would otherwise be considered waste, its application
greatly depends on the value of the metal to be recovered. A major challenge is
to find a suitable match between an ore body and biomining technology and to
identify suitable concentration and size which allow economic recovery.

59. References
• Alvorado Oscar. 2011. Mining Safety: Bioleaching Bacteria Clean Toxic
Mine Tailings," Global Mining,
• Abhilash et al. 2010. Bioleaching - An Alternate Uranium Ore Processing
Technology for India. 158-162p.
• K.A. Natarajan . 2006. Biotechnology for Metal Extraction, - Mineral
Beneficiation andEnvironmental Control. Proceedings of the International
Seminar on Mineral Processing Technology Chennai, India. pp. 68 - 81
• Mohd. Haris Siddiqui. 2009. Biomining - A Useful Approach Toward
Metal Extraction. American-Eurasian Journal of Agronomy 2 (2): 84-88,
2009
• Torsten von Rozycki Æ Dietrich H. Nies. 2008 Cupriavidus metallidurans:
evolution of a metal-resistant bacterium. Review paper