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. Microorganisms are used because they can: lower the production costs. cause less environmental pollution in comparison to the traditional leaching methods. very efficiently extract metals when their concentration in the ore is low.

1. ENRICHMENT OF ORES BY
MICROORGANISMS
Bioaccumulation and
biomineralization

2.  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.
Microorganisms are used because they can:
 lower the production costs.
 cause less environmental pollution in comparison
to the traditional leaching methods.
 very efficiently extract metals when their
concentration in the ore is low.

3. THE LEACHING PROCESS
 Bacteria perform the key reaction of regenerating the
major ore oxidizer which in most cases is ferric iron as
well as further ore oxidation. The reaction is
performed at the bacterial cell membrane. In the
process, free electrons are generated and used for
the reduction of oxygen to water which produces
energy in the bacterial cell.
 Ores, like pyrite (FeS2), are first oxidized by ferric iron
(Fe3+) to thiosulfate (S2O3
2-) in the absence of
bacteria.
 In the first step, disulfide is spontaneously oxidized to
thiosulfate by ferric iron (Fe3+), which in turn is
reduced to give ferrous iron (Fe2+):
 (1) FeS2+6Fe3++3H2O⟶7Fe2++S2O2−3+6H+spont
aneous

4.  Bacteria are added in the second step and recover
Fe3+ from ferrous iron (Fe2+) which is then reused in the
first step of leaching:
 (2) 4Fe2++O2+4H+⟶4Fe3++2H2O(iron
oxidizers)4Fe2++O2+4H+⟶4Fe3++2H2O(iron oxidizers)
 Thiosulfate is also oxidized by bacteria to give sulfate:
 (3) S2O2−3+2O2+H2O⟶2SO2−4+2H+(sulfur
oxidizers)S2O32−+2O2+H2O⟶2SO42−+2H+(sulfur
oxidizers)
 The ferric iron produced in reaction (2) oxidized more
sulfide as in reaction (1), closing the cycle and given the
net reaction:
 (4) 2FeS2+7O2+2H2O⟶2Fe2++4SO2−4+4H+2FeS2+7O
2+2H2O⟶2Fe2++4SO42−+4H+
 The net products of the reaction are soluble ferrous sulfate
and sulfuric acid.

5.  The microbial oxidation 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
while reducing oxygen to water. The critical
reaction is the oxidation of sulfide by ferric iron.
The main role of the bacterial step is the
regeneration of this reactant.
 Copper leaching has a very similar mechanism.

6. Sulfide mineral bacterial leaching: Bacterial cells
oxidizing the ferrous iron back to ferric iron while using
slightly different contact mechanisms with the metal.

7. Microorganisms Capable of Ore
Leaching
 Bioleaching reactions industrially are performed
by many bacterial species that can oxidize
ferrous iron and sulfur. An example of such
species is Acidithiobacillus ferroxidans. Some
fungi species (Aspergillus niger and Penicillium
simplicissimum) have also been shown to have
the ability to dissolute heavy metals. When fungi
are used, the leaching mechanism is different.
The fungi use the acids that they produce in their
metabolic reactions to dissolve the metal.

8.  In general, bioleaching is cleaner and safer for
the environment than chemical processing.
However environmental pollution with toxic
products, like sulfuric acid from the pyrite
leaching, and heavy metals is still possible.
Another drawback of microbial leaching is the
slow rate at which microbes work.

9. MOST COMMONLY USED
MICROBES
 The most commonly used microorganisms in
bioleaching are; o Thiobacillus thiooxidants
 o Thiobacillus ferrooxidants
 other microorganisms which may also be used
are;
 Bacillus Licheniformis,
 B. luteus, B megaterium,
 B polymyxa,
 B leptospirillum ferrooxidants,
 Pseudomonas flurescens,
 Sulfolobus acidocaldarius, etc;

10.  Thiobacillus thiooxidant and T. ferrooxidants
have always been found to be present on the
leaching dump
 The specie of thiobacillus is most extensively
studied gram –ve bacteria which derives energy
from oxidation of fe2

11.  The reactions mechanisms are two types, i.e.,
 • Direct bacterial leaching
 • Indirect bacterial leaching

12. DIRECT
 Direct bacterial leaching in this process, a
physical contact exist between bacteria and ores
and oxidation of minerals takes place though
enzymatically catalysed steps ex; pyrite is
oxidised to ferric sulphate 2FeS2+7O2+2H2O
2FeSo4+2H2So4

13. INDIRECT
 Indirect bacterial leaching in this process the
microbes are not in direct contact with minerals,
but leaching agents are produced by these
microbes which oxidize the ores.

14. COMERCIAL BIOLEACHING
 There are three commercial process used in
bioleaching;
 a. Slope leaching
 b. Heap leaching
 c. In situ leaching

15. SLOPE LEACHING
 Here the ores are first ground to get fine pieces
and then dumped into large leaching dump
 Water containing inoculum of thiobacillus is
continuously sprinkled over the ore
 Water is collected from the bottom and used to
extract metals and generate bacteria in an
oxidation pond

16. HEAP LEACHING
 In this process the ore remains in its original
position in earth. Surface blasting of earth is
done to increase the permeability of water.
 Water containing thiobacillus is pumped through
drilled passages to the ores .
 Acidic water seeps through the rock and collects
at bottom
 Again, water is pumped from bottom .
 Mineral is extracted and water is reused after
generation of bacteria

17. IN SITU LEACHING
 Ores of copper from which copper is recovered
are,
 Chalcocite(Cu2S)
 Chalcopyrite(CuFeS2)
 Covellite(CuS)
 Copper leaching is operated as simple heap
leaching and in situ leaching process
 Dilute sulphuric acid is percolated down through
the pile
 Liquid coming out of bottom of pile reach in
mineral
 Liquid is collected and transported to
precipitation plant

18.  Chalcocite is oxidized to soluble form of copper
Cu2S+O2+ CuS+Cu2+ +H2O .Thereafter
chemical reactions occur, i.e. CuS+8Fe +4H2O -
Cu+8Fe+SO4+8H Copper is removed,
Fe0+Cu Cu+Fe2+ Fe2+ is transferred to
oxidation pond Fe+1/4(O2)+H+ Fe3+ +1/2(H2O)
 Fe3+ ions produced is an oxidation of ore
 It is pumped back to pile
 Sulphuric acid is added to maintain pH

19.  Uranium is extracted when insoluble tetravalent
uranium is oxidized with a hot H2So4/FeSo4
solution to make hexavalent uranium sulphate
 pH required for the reaction is 1.5-3.5
 Temperature: around 35 degree C following
reaction takes place, U2O+Fe2(SO4)3
UO2SO4+2FeSO4
 Uranium leaching is an indirect process
 When T.ferrooxidants are involved in uranium
extraction, they do not directly attack on ore but
on the iron oxidants.
 The pyrite reaction is used for the initial
production of Fe Reaction; 2FeS+H2O+7 ½[O2]
Fe2[SO4]3+ H2SO4

20.  Microbial leaching of refractory process metal
ores to enhance gold and silver recovery is one of
the promising applications
 Gold is obtained through bioleaching of
arsenopyrite/pyrite
 Silver is also obtained by bioleaching of
arsenopyrite but it is more readily solubilized than
gold during microbial leaching of iron sulphide.

21.  Ores of silica
 Magnesite
 Bauxite
 Dolomite
 Basalt
 Mohanty et al.,(1990) isolated Bacillus
licheniformis from magnesite ore deposits . Later,
it was shown to be associated with bioleaching,
concomitant mineralysis and silican uptake by the
bacterium

22. BIOMINERALIZATION
 Microbes play geo active role in biosphere .
 All kind of microbes include prokaryotes and
Eukaryotes , their symbiotic association etc.
contribute geological phenomena and many
geological processes like metal and mineral
transformation.
 The ubiquity and importance of microbes in
biosphere processes.

23.  A process by which living forms influences the
precipitation of mineral materials.
 The process creates heterogeneous
accumulation composites composed of biogenic
and inorganic compounds.
 Living forms produces carbonates phosphate
oxalates silica iron or sulfur containing minerals.
 Biomineralization occurs extracellular involves
often crystalline, materials forming on the outer
wall of the cell.
 Intracellular biomineralization is mineral
formation within the cell such as calcite formation
for the group of the algae the Coccolithophorides.

24. TYPES OF MINERALIZATION
 Mineral synthesis can be categorized into two
categories: Biologically Induced Mineralization
Biologically Controlled Mineralization

25. BIOLOGICALLY INDUCED
MINERALIZATION
 Mineral forms by this process, generally nucleate
& grow extracellulary as a result of metabolic
activity.
 Subsequent chemical reaction involving
metabolic by products such as O2, HCO-3, etc.
 In some the organisms secrete one or more
metabolic products that react with ions or
compounds in the environment resulting on the
subsequent deposition of mineral particles.

26. MICROBES INVOLVES IN BIM
 No of microbes involves in biologically Induced
mineralization process .
 Some of microbes are: Mycorrhiza, Lichen,
Cynobacteria like Synechococcus spp.,
 Bacteria like Leptospirillum spp. , Thiobacillus
ferroxidans, sulfur reducing bacteria etc.
 Archea like sulfolobus spp., Acidimicrobium
ferroxidans spp., acidianus spp., Metallosphaera
spp., sulfurococcus yellowstonesis. etc.

27. EXAMPLES OF MINERAL BY
BIM
 Calcium Carbonate: Carbonate are long lived
locally abundant sediments, promotes calcite/
Aragonite and Dolomite precipitates. o These
precipitates occurs in, on or around the organic
matter of the cells that they produce. o These
carbonate minerals presents on lake, sea floors
etc. Chemical Reaction: Ca2+ + 2HCO3- ↔
CaCO3 + CO2 + H2O Microbial populations
involved in this mineral formation are :
Cynobacteria, Algae such as green, brown, red
algae and Chrysophytes such as
Coccolithophores & few protozoa like Forminifera.

28. BIOLOGICALLY CONTROLLED
MINERALIZATION
 Microbes exerts considerable active control over
all aspects of the nucleation and mineral growth
stages.
 A specific site within the cytoplasm or the cell wall
is sealed off from the external environment
creating geochemical condition independently.
 2 common methods of space delineation can
occur. 1. Involve the development of intercellular
space between cells. 2. Formation of intracellular
deposition vesicles.

29.  Once the cellular compartment is formed the cells
sequestering specific ions of choice transferring
them to mineralization site , where conc.
Increased until saturation achieved Super
saturation are then regulated by managing the
rate at which mineral constituents are brought
into the cell via specific transport enzymes.
nucleation controlled by exposing organic ligands
with distinct sterochemical and electrochemical
properties tailored to interact with the mineralizing
ions.

30. MICROBES INVOLVE IN BCM
 Many microbes involves in biologically controlled
mineralization process These are: Magnetotactic
bacteria Diatoms Emiliania huxleyi etc

31. EXAMPLE OF MINERAL BY
BCM
 Magnetite: Magnetite formation done by
Magnetotactic Bacteria, which is microaerophilic,
posses bidirectional motility and contain
membrane bounded a no of intracellular, linear
arranged magnetosomes , house mineral grains.
The actual crystallization of magnetite then
involves the reaction of the ferric hydroxide with
more Fe2+: Fe2+ + 2OH− + 2Fe(OH)3→Fe3O4 +
4H2O

32. SIGNIFICANCES OF
BIOMINERALIZATION
 Great significance in scientific and commercial
application
 Metal sorption, precipitate can be important and
useful in metal and radionuclide removal during
bioremediation metal radionuclide contaminate
water .
 Efficiently removal of Fe and Mn ions from water
in waste water treatment plants.

34. BIOMAGNIFICATION AND
BIOACCUMULATION
 Biomagnification It is also known as
bioamplification or biological magnification It is
the increase in concentration of a pollutant that
occurs in a food chain as a consequence of: 1.
Persistence (can't be broken down by
environmental processes) 2. Bioenergetics in the
food chain 3. Low rate of internal
degradation/excretion of the substance often due
to water-insolubility

35.  Biomagnification occurs when substances such
as pesticides or heavy metals move up the food
chain by working their way into the environment. •
e.g. Pollutants in rivers or lakes are taken up by
microorganisms like plankton and are eaten by
aquatic organisms such as fish, which in turn are
eaten by large birds, animals and humans. The
substances become concentrated in tissues or
internal organs as they move up the chain.

36.  As a result,organisms at the top of the food chain
generally suffer greater harm from a persistent
toxin or pollutant than those at lower levels
Because •At each level of the food chain there is
a lot of energy loss, a predator must consume
many prey, including all of their lipophilic
substances and fats which carries the pollutant,
which then accumulates in the fats of the
predator.

37.  Biomagnification can occur in almost all types of
ecosystems.e.g terrestrial,aquatic
 •Bioaccumulants are toxic substances that increase in
concentration in tissues of living organisms. They
enter the organism through contaminated air, water,
or food and are very slowly metabolized or excreted.
 •Bioaccumulation is the concentration of pollutant
from the environment which occurs within a trophic
level, i.e. one level of a food chain, usually the first
organism in the food chain
 •Where as biomagnification is the concentration of
pollutant across the food chain

38.  In order for biomagnification to occur, the pollutant must
be: 1.long-lived 2.mobile 3.soluble in fats 4.biologically
active Persistent
 Persistent pollutant vs. short lived pollutant
 • If a pollutant is short-lived, it will be broken down before
it can become dangerous.
 • If it is not mobile, it will stay in one place and is unlikely to
be taken up by organisms.
 • If the pollutant is soluble in water it will be excreted by the
organism.
 • Pollutants that dissolve in fats(Persistent pollutants) are
retained for a long time.
 • Lipid or fat soluble substances cannot be diluted, broken
down, or excreted in urine.
 • They accumulate in fatty tissues of an organism if the
organism lacks enzymes to degrade them.

39.  DDT :dichloro diphenyl trichloroethane.
 •chlorinated hydrocarbon,used as pesticide
 •DDT has a half-life: 15 years, which means if you
use 100 kg of DDT, it will break down as follows:
Year Amount Remaining 0 100 kg 15 50 kg 30 25
kg 45 12.5 kg 60 6.25 kg 75 3.13 kg 90 1.56 kg
105 0.78 kg 120 0.39 kg

40. BIOCONCENTRATION
 Bioconcentration is a term used specifically in
reference to aquatic environments and aquatic
organisms, in contrast with the related
“bioaccumulation,” which can refer to toxins and
organisms found in a variety of environments.
•The substance(pollutant) can also be taken up
by organism from surrounding water by non
dietary routes. e.g. through the gills of a
fish,which travels through blood to the lipid tissue.
 Bioconcentration factor can be expressed as: The
ratio of the concentration of a chemical in an
organism to the concentration of the chemical in
the surrounding environment.

41.  It can also be defined as the rate of substance
uptake/rate of substance elimination
 The higher the ratio, the more severe the
bioconcentration.
 A high BCF can lead to health problems such as
genetic mutations passed on to offsprings In fish
populations increasing numbers of fish born with
ambiguous genitalia have been identified in
waterways contaminated with pharmaceuticals.

42. MERCURY POISONING
 Alarming levels of toxic mercury were found in 264
samples of popular fish (like Rohu, Bhola, Tangra,
Aar, Bhetki and other fish varieties )collected across
West Bengal .[organisations :Toxics Link and DISHA
on 2012]
 •The trend is applicable across the country
 •While 52 cases had mercury concentrates in excess
of the Prevention of Food Adulteration (PFA) Act
standards of 0.5 ppm
 • 129 of the fish showed methyl mercury levels (a
metabolized and more poisonous form of mercury)
exceeding the 0.25 ppm PFA stipulations. Mercury
levels in fish across West Bengal
 Causes •coal firing •mining •thermal plants •industrial
effluents directly discharged into water bodies
•municipal waste water streams.

43.  High level of mercury causes: neurotoxicity and
impairs motor skills ,stunts psychological
development and growth can cause serious
mental disorders over a gradual period of time
 Biodiversity Research Institute in Maine ,August
2013 estimated that 83% of fish worldwide have
unsafe mercury levels Over 50% of Asian
population have more than the 5ug/ml mercury
level in blood Cause for global concern because:
•Most Seafood is imported and exported
•Pollution is World-wide problem, requires
cooperation of various nations. E.g. pollution of
the ocean and seas