Transcript Biogenesis and Biodegradation of Sulfide Minerals at Earth`s Surface

Biogenesis and Biodegradation of
Sulfide Minerals at Earth’s Surface
Geomicrobiology of Sulfide Minerals
Aldyla Nisa Raditya
Astri Elia
Ariani Intan Utami
Venessa Alia
Vilandri Astarini
Annissa Kurnia Maulida
Zara Zentira
10407013
10407015
10407016
10407032
10407035
10407040
10607053
GROUP 4
SCHOOL OF LIFE SCIENCES AND TECHNOLOGY
BANDUNG INSTITUTE OF TECHNOLOGY
2010
Introduction
Natural
Origin of
Metal
Sulfides
Formation of
Acid Coal
Mine
Drainage
Outline
Bioextraction
of Metal
Sulfides Ores
by
Complexation
Principles of
Metal Sulfide
Formation
Bioleaching
of Metal
Sulfide &
Uraninite
Ores
Biooxidation
of Metal
Sulfides
Introduction
SULFIDE MINERALS AT A GLANCE
-2
Sulfide = S-2
-2
+6
0
€ $ Rp = Cu, Ni, Zn, Co
Metal ions + oxidized sulfides
REDUCTION
OXIDATION
Other microbes
Some
sedimentary
environments
Sulfate-reducing bacteria (SRB)
Sulfate
•Soil
•Sediments
•Rock surfaces
Metal sulfides
Sulfide minerals
FeS (pyrite)
Metal industry
utilization
Bioextraction
(bioleaching)
Biobeneficiation
(microbial pretreatment to
remove pyrite from gold ores)
Ore biogenesis
Ore biomobilization
Bioleaching
Where it comes
NATURAL ORIGIN OF METAL
SULFIDES
Natural
Origin of
Metal
Sulfides
Abiotic
Origin
• Hydrothremal
origin
Biotic
Origin
• Sedimentary
metal sulfides
of biotic origin
Hydrothermal Origin (Abiotic)
Igneous origin
Most metal sulfides
(including those of
commercial interest)
A result of subduction
of oceanic crust,
enriched in Cu with
hydrothermal activity
at mid-ocean
spreading-centers
Formation
Terrestrial deposit of
porphyry copper ore
Current theory:
The help of plate tectonics
White smokers
Metal sulfide “smoke”
(black mineral)
Cooling
outside the
oceanic crust
Deposited as the vents
(chalcopyrite CuFeS2,
sphalerite ZnS)
 Relatively more significant
quantity of metal sulfides
deposition occurs
 The brine is cooler than
that of black smoker’s
White smoke is depleted in
some base metals, but still
contains major quantities of
Fe, Mn, & H2S
Metal sulfide (black
mineral) presipitated
inside the crust
Seawater
Magma heat
Cooling in upper oceanic crust
Sedimentary Metal Sulfides of Biogenic Origin
relatively
rare
Nonferrous
sulfides
Burried in
formed sediment
Hydrothermal or
microbial origin
Metal sulfides = metal compound + H2S
Iron sulfides
most
common
reducing zone in
sedimentary deposits in
estuarine environment
(peat, salt marsh)
Plentiful supply
of sulfate
IMPORTANT
Bacterial reduction
(anaerobic)
Each >1% metal deposited
needs 0.1% carbon (dry
weight) and an enriched
source of metals (e.g.
hydrothermal solution)
Metal sulfides = iron compound + H2S
Iron pyrite (FeS2)
Not a
permanent sink
for iron
Seasonal reoxidation
as conditions in the
environment change
from
reducing to oxidizing
Back to basics, always
PRINCIPLES OF METAL SULFIDE
FORMATION
• Metal Sulfide in nature
interaction between an appropriate metal ion and
biogenically
or abiogenically formed sulfide ion:
M2+ + S2- →MS
Biogenik
bacterial sulfate
reduction
Abiogenik
from bacterial mineralization of
organic
sulfur-containing compounds
• Solubility Products for Some Metal Sulfides
Because of their relative insolubility, the
metal sulfides form readily at ambient temperatures
and pressures.
• case of amorphous iron sulfide (FeS) formation
The ionization constant
for FeS
The ionization constant
for H2S
The constant for the
dissociation of H2S into
HS- and H+
The constant for the
dissociation of HS- into
S2- and H+
[Fe2+][S2-]=
10-19
1
[Fe2+] = [H+]2/[H2S] x 10-19/10-21,96
= [H+]2/[H2S] x 1021,96
[S2-]= 10-21,96 [H2S]/[H+]2
3
[HS-][H+]/[H2S]= 10-6,96
4
[S2-][H+]/[HS-]= 10-15
2
LABORATORY EVIDENCE IN SUPPORT OF
BIOGENESIS
OF METAL SULFIDES
Batch Cultures
Miller
(1949,1950)
cobalt sulfide on
bismuth
sulfide
addition
of 2CoCO3
,on addition
· 3Co(OH)2,
of (BiO2)2CO3 ·H2O,
nickel sulfide on
addition of NiCO3
or Ni(OH)2
reported that sulfides of Sb, Bi, Co, Cd, Fe, Pb, Ni, and Zn
were
formed in a lactate-containing broth culture of Desulfovibrio
desulfuricans to which insoluble salts of selected metals had
been added.
minimize metal
toxicity for D.
desulfuricans
Metal ion toxicity depends in
part on the solubility of
the metal compound from
which the ion derives
Desulfovibrio desulfuricans and Desulfotomaculum sp. (Clostridium
Desulfuricans). They grew them in lactate or acetate medium
containing steel wool. The media were saline to simulate marine
(near-shore and estuarine) conditions under which the
sourceinvestigators
of
thought the reactions are likely to occur in nature.
hydrogen for the
The
bacterial
Baas Becking
hydrogen resulted from corrosion of the steel
reduction of
and Moore
wool by the spontaneous reaction,
(1961) sulfate
Fe0 + 2H2O → H2 + Fe(OH)2
used by the sulfatereducers in the
4H2 + SO42- + 2H+  H2S + 4H2O
formation of hydrogen
sulfide.
They succeeded in forming covellite from
to form
cinnabar
where Miller (1950) failed,unable
probably
Argentite
(Agmalachite
S)from
from
silver
ZnS
unable
to form
alabandite (MnS)
2from
Ferrous
Covellite
Galena
(PbS)
sulfide
(CuS)
from
PbCO
3
ZnS
from(Ag
ZnCO
(HgS)
from mercuric
because
they
chloride
ClO23) and
silverperformed
from
MnCO3
or Cu5FeS4 or CuFeS2
2
FePO
Malachite
and
[PbCO
and
[CuCO
Fe
.Pb(OH)
.Cu(OH)
]
]
4
3 2 33 2
2
carbonate
their 3experiment
in a saline medium from
(3% NaCl)
carbonate (AgCO
)
a mixture of Cu2O or malachite
in which Cl− could complex Cu2+, thereby
and hematite and lepidochrosite.
increasing the solubility of Cu2+.
COLUMN EXPERIMENT: MODEL FOR BIOGENESIS
OF SEDIMENTARY METAL SULFIDES
BIOOXIDATION OF METAL SULFIDES
Microorganisms Involved in
Biooxidation of Metal Sulfides
Microorganisms
Moderate
thermophiles
Mesophiles
Acidithiobacillus
ferrooxidans
Leptospirillum
ferrooxidans
Ferroplasma
acidiphilum
(Archaea)
F. Acidarmanus
(Archaea)
Alicyclobacillus
tolerans
Acidimicrobium
ferrooxidans
Extreme
thermophiles
Sulfolobus spp.
(Archaea)
Acidianus
brierleyi
(Archaea)
Mesophile Bacteria
• F. acidarmanus grow best in a
pH range of ∼1.5–2.5. F.
acidarmanus, a recent
discovery, grows at a pH as low
as 0 (optimum pH 1.2) at a
temperature of ∼40°C.
• F. acidiphilum grows in a pH
range of 1.3–2.2 (optimum pH
1.7) in a temperature range of
15–45°C
• Acidithiobacillus ferrooxidans
secreted EPS formation. The
EPSs enable attachment to
sulfide mineral surfaces.
• L. ferrooxidans
(Mesophile) and
Acidimicrobium
ferrooxidans
(Moderate
thermophile) can
promote metal sulfide
oxidation only by
generating Fe3+ from
dissolved Fe2+ which
then oxidizes metal
sulfide abiotically
Acidimicrobium ferrooxidans
Extreme Thermophile
• Acidianus brierleyi and
Sulfolobus sp. can
oxidize a variety of metal
sulfides including pyrite,
marcasite, arsenopyrite,
chalcopyrite, NiS, and
probably CoS.
• A. brierleyi can oxidize
molybdenite in the
absence of added iron
• molybdate ion is less
toxic to Acidianus
brierleyi
Acidianus brierleyi
Sulfolobus sp
INTERACTION IN MICROBIAL
OXIDATION
Direct
the microbes
oxidize a metal
sulfide in physical
contact with the
mineral surface.
Indirect
microbes usually
generate an
oxidant (commonly
ferric iron from
ferrous iron) in the
bulk phase.
Interaction in
microbial
oxidation
Direct oxidation
• microbes have to be in intimate contact with
the mineral they attack (enzymatic oxidation)
• Bacterial attachment to mineral sulfide
surfaces at specific sites
• Some evidence suggests that direct microbial
attack is initiated at sites of crystal
imperfections
• a collective model is that bacterial cells
possessing this ability act as catalytic
conductors
• in transferring electrons
from cathodic areas on
crystal surfaces of a metal
sulfide via an electron
transport system in the cell
envelope to oxygen
• In this model :
cell attached to the surface
of a Cu2S particle (acts as
a conductor) electrons it
removes in the oxidation
of Cu(I) of Cu2S and
transfers to oxygen.
• the outer membrane
of Acidithiobacillus
ferrooxidans
contains a highmolecular weight ctype cytochrome
Cyc2 that has the
capacity to promote
the oxidation of Fe2+
to Fe3+ at the outer
surface of the outer
membrane. (Yarzabal
et al., 2002)
Biooxidation of Sulfide Minerals
Indirect Oxidation
Indirect Oxidation
MICROBES
oxidant
(Fe3+)
Oxidize
metal ores
Indirect Oxidation
It may be generated initially from dissolved
ferrous iron (Fe2+) at:
1. pH 3.5 – 5 in a mesophilic temperature range by
Metallogenium
2. pH <3.5 in a mesophilic temperature by
Acidithiobacillus ferrooxidans and
Leptospirillum ferrooxidans
3. thermophilic temperature by Sulfolobus spp,
Acidianus brierleyi and Alicyclobacillus tolerans
Indirect Oxidation
Ferric iron in acid solution acts as an oxidant
of the metal sulfides in indirect attack:
MS + 2Fe3+ → M2+ + S0 + 2Fe2+
* A central role of Acidithiobacillus
ferrooxidans in an indirect oxidation process
is to regenerate Fe3 + from the Fe2+ formed
Indirect Oxidation
Ferric iron can be generated from iron
pyrites (FeS2) by indirect attack by
Acidithiobacillus ferrooxidans and other
iron-oxidizing acidophiles
Further oxidation to sulfuric acid (H2SO4)
is very slow but is likely to be greatly
accelerated by microorganisms such as
Acidithiobacillus thiooxidans
Pyrite Oxidation
Elemental sulfur may form a film on the surface of
metal sulfide crystals in chemical oxidation and
interfere with further chemical oxidation of the residual
metal sulfide
The chemical oxidation of metal sulfides must occur in
acid solution below pH 5 to keep enough ferric iron in
solution.
Biooxidation of Sulfide Minerals
Pyrite Oxidation
Pyrite Oxidation
Acidithiobacillus ferrooxidans represents a special
case in which direct and indirect oxidation of the
mineral CANNOT BE READILY SEPARATED because
ferric iron is ALWAYS a product.
Experimentally, there ara 4 phases in the leaching
of pyrite by
Acidithiobacillus ferrooxidans in a stirred reactor.
Pyrite Oxidation
The first phase (5 days):
- unattached bacteria (planctonic) decerase
- small amount of dissolved ferric iron added with
the inoculum reacted with some of the pyrite.
The second phase (5 days):
- Start of pyrite dissolution with oxidation of its iron and
sulfur
- Planktonic bacteria multiexponentially and the pH
began to drop
Pyrite Oxidation
The third phase (10 days) :
Significant increase in dissolved ferric iron, the ferrous
iron concentration remaining low
Planktonic
bacteria
continued
to
increase
exponentially, pH continued to drop
The fourth phase (25 days) :
- The dissolved Fe(III)/Fe(II) ratio decreased, iron and
sulfur strongly oxidized, and the planktonic bacteria
reached a stationary phase
- The surface of the pyrite particles now showed easily
recognizable square or hexagonal corrosion pits.
Oxidation of Iron Pyrite (FeS2)
BIOLEACHING OF METAL SULFIDES
AND URANINITE ORES
METAL SULFIDE ORES
• Low-grade sulfide ores generally contain metal values at
concentrations below 0.5% (w/w).
• Bioleaching was used commercially only with low-grade
portions of an ore and with ore tailings→ it is now also used in
treating high-grade ore and ore concentrates.
• Ore heaps may consist of high grade ore.
The lixiviant
• As a fine spray onto ore heaps and dumps → avoids waterlogging
waterlogging
exclude
needed oxygen
(anaerobic
conditions)
bacteria
reduce ferric
to ferrous iron
and others
that reduce
sulfate to H2S
lower the
ferric iron
concentration
for chemical
oxidation of
metal sulfides
in the anoxic
zone
The sulfate-reducers
cause metal species
mobilized in the
oxidized zones to
reprecipitate as
sulfides
• makes possible the growth and multiplication of appropriate acidophilic
iron-oxidizers and the oxidation of pyrite, chalcopyrite, and nonferrous
metal sulfides in the ore.
as microbial and chemical activities continue → the solution in the heaps/dumps
becomes charged with dissolved metal values → after issuing from the
heaps/dumps it is collected as pregnant
solution
Copper Separation:
treatment of pregnant
solution with sponge iron
(Fe0)
•
The sponge iron precipitated the copper
by cementation in a process
Cu2+ + Fe0 → Cu0 + Fe2+
(The copper metal: very impure and required further refinement by smelting)
metal value is
stripped by
CEMENTATION
BARREN
SOLUTION
significantly
enriched in
Fe2+
excess of
ferrous iron
Removal
(biooxidation in
oxidation ponds)
the oxidation of
the ferrous iron
with concomitant
acidification
precipitate on
the ore mineral
surfaces
excessive jarosite
(KFe3(SO4)2(OH)6)
formation
interfering with
further
oxidation
clog the
drainage
channels in the
ore heaps
/dumps
oxidized iron
precipitated as
basic ferric
sulfates,
including jarosite
reintroduced
into the
heap/dump,
the residual
iron caused
indirect
leaching of the
metal sulfides
Barren solution that entered the heaps/dumps caused;
Weathering of
the host rock
Liberation of
aluminum and
aluminosilicates
High acidity of the lixiviant may also play an important role
in preventing metal ions formed during leaching from being adsorbed by the
host rock(Ehrlich, 1977; Ehrlich and Fox, 1967).
Method of Recovering Metal Values
from Pregnant Solution:
electrowinning
(the pregnant solution contains
only one major metal value)
electrolytic process → metal to be
recovered is deposited on a cathode made
of the same metal.
Advantage: high purity and normally does
not need further refining; not raising the
ferrous iron concentration in barren
solution.
solvent extraction
(when the pregnant solution
contains several different metal
values)
followed by electrowinning of each
of the separated metal values
Introduce reagents into the barren
solution that are inhibitory to the
bacteria involved in leaching
The acidophilic iron-oxidizing bacteria
Generate Acidic
ferric sulfate
Lixiviant
Attack the
mineral sulfides
directly
The heating of the interior ore
dumps/heaps can be accelerated
by bacterial action →metal sulfide
oxidation is an exothermic process
↓
The interior temperature (70-80°C)
→ unfavorable for the growth of
mesophilic bioleaching bacteria
(Acidithiobacillus ferrooxidans and
Leptospirillum ferrooxidans) in the
interior
↓
Leaching process in dumps/heaps
of metal sulfide ores is
mostly abiotic.
Leptospirillum
ferrooxidans
Acidithiobacillus
ferrooxidans
• Thermophiles capable of promoting
bioleaching of metal sulfides, by acidophilic
→ iron-oxidizing thermophiles → operate
optimally at the higher temperatures.
• Leaching in all parts of a heap or dump is
most likely biological.
• Thermophiles may be responsible for
regulating the internal temperature of
active leach heaps/dumps
COPPER SULFIDE ORES
Primary Copper
Mineral
• Chalcopyrite (CuFeS2)
Secondary Copper • Chalcocite (Cu2S)
Sulfide Minerals • Covellite (CuS)
• The oxidation of chalcopyrite enhanced by Acidithiobacillus ferrooxidans
and Acidianus brierleyi (Razzell and Trussell, 1963; Brierley, 1974).
• Ferric iron > 1000 ppm → it precipitates as jarosite or adsorbs to the
surface of chalcopyrite crystals and prevents further oxidation → inhibit
chalcopyrite oxidation
• Bacteria interfere by generating excess ferric iron from ferrous iron that
precipitates or is adsorbed by residual chalcopyrite.
Heap, dump, and in situ leaching
operations do not require
inoculation with active bacteria
(Brierley et al., 1995).
Reactor leaching operations greatly benefit
from inoculation with a strain selected for
enhanced activity.
The inoculum has to be massive → outgrow
the organisms naturally present on the ore.
Schematic representation of a bioleach circuit for heap or dump leaching of
copper sulfide ore
URANINITE (URANIUM OXIDE) LEACHING
Uranium is found in
some igneous and
sedimentary rocks in
the form of UO2 or
Uranium (VI) oxides
which are radioactives.
The principles of bioleaching
have also been applied on a
practical scale to the leaching of
uraninite ores, especially if the
ores are low grade. The process
may involve dump, heap, or in
situ leaching (Wadden and Gallant,
1985; McCready and Gould, 1990)
Using Acidithiobacillus
ferrooxidans in the process.
The process proceeds indirectly by generating:
• Oxidized lixiviant
• Acid ferric sulfate (Fe (III) sulfate), oxidizing U(IV) into U(VI) in soluble form
2Fe2+
+ 0.5O2H +
2H+
:
→ 2Fe3+ + H2O
Fe3+ + 3H2O → Fe(OH)3 + 3H+
• Ferric iron or Fe (III) oxide is hydrolized generating acid
UO2 + 2Fe3+ → UO22+ + 2Fe2+
• Insoluble ferric iron reacts with uranium dioxide
generating uranil ions
UO22+ + H2S → UO2 + 2H+ + S0
• These bacteria can reprecipitate UO2 as a result of
reaction of UO22+ with H2S
URANIUM BIOLEACHING → artificially stimulated
• Must occur on a very limited scale and thus
only result in slow mobilization of uranium.
• UO22+ in drainage → microbiologically
precipitated by its reduction under anaerobic
conditions to insoluble UO2.
• Geobacter metallireducens and Shewanella
→ precipitating U(IV) under anaerobic
conditions (Gorby and Lovley, 1992).
• The electron donors used:
– organic compounds
– H2 in the case of some sulfate-reducers
and Shewanella
MOBILIZATION OF URANIUM IN GRANITIC ROCKS BY
HETEROTROPHS
Heterotrophic microorganisms such as some
members of the soil microflora and bacteria from
granites or mine waters (Pseudomonas fluorescens, P.
putida, and Achromobacter) can mobilize uranium in
granitic rocks, ore, and sand by weathering that
results from mineral interaction with organic acids
and chelators produced by the microorganisms.
Magne et al. found experimentally:
• Addition of thymol to percolation columns of uraniferous material fed with
glucose solution selected a microbial flora whose effi ciency in uranium
mobilization was improved by greater production of oxalic acid
• Phenolic and quinoid compounds (secondary metabolites of plant) could replace
the role of thymol
• Microorganisms could presipitate uranium through complex uranium solution
digestion, that is, by microbial destruction of the organic moiety that complexes
the uranium
The experiment explains how uranium in granitic rocks could
basically be mobilized and presipitated by bacteria and
concentrated in another place under the influence of other
microbes
STUDY OF BIOLEACHING KINETICS
A number of experiments about bioleaching of sulfide
mineral in the presence of ferrous iron has been
published
• Boon et al. (1995), Hansford (1997), Hansford andVargas (1999),
Crundwell (1995, 1997), Nordstrom andSoutham (1997), Driessens et
al. (1999), Fowler and Crundwell (1999), and Howard dan Crundwell
(1999).
Assumption and conclusion is that bioleaching of metal
sulfides happens concurrently in the same leaching
operation appears to have been rejected.
• However, Fowler and Crundwell (1999) do assign oxidation of S0 that
appears at the surface of ZnS during leaching to attached
Acidithiobacillus ferrooxidans cells.
INDUSTRIAL v.s.NATURAL BIOLEACHING
BIOEXTRACTION OF METAL SULFIDE
ORES BY COMPLEXATION
oxidized by
Metal sulfide ores
acidophilic iron-oxidizing bacteria
an amount of acid-consuming
constituents in the host rock
extracted by :
• • Penicillium
Aspergillussp.
sp.
complexing agents
mine-tailings pond of the White
unidentified metabolites
Pine Copper Co. in Michigan mobilization of copper in an oxidized
mining residue by A. niger in a sucrose–
mineral salts medium.
mobilize copper from sedimentary ores Czapek’s broth
contain : sucrose, NaNO3, cysteine, methionine, or
glutamic
acid as well as ligands of metal ions
The chief mobilizing agents
act
as acidulants
gluconic and citric acids
Wenberg et al. (1971)
grew fungus in the presence of copper
ore (sulfide or native copper minerals
with basic gangue constituents)
addition of citrate
lowered the toxicity of the extracted copper
when the fungus was grown in the presence of the ore
obtained better results
grew the fungus in the absence of the ore
treated the ore with the spent
medium from the fungus culture
by forming complexes
The organisms
forms ligands
extracted the metals
from the ores
more stable than the original insoluble
form of the metals in the ores
MA+ HCh → MCh + H+ + A−
MA : metal salt (mineral)
HCh : ligand (chelating agent)
MCh : the resultant metal chelate
A− : the counter ion of the original metal salt (S2−)
The S2− may undergo chemical or bacterial oxidation
(Chemical Processing, 1965)
FORMATION OF ACID COAL MINE
DRAINAGE
Acid Mine Drainage
• Yellow boy in a stream receiving acid
Air, bacteria and
Pyrite
drainage from surface
coalduring
mining.
moisture
mining
An Enviromental problem in coalMining region
Initiator
reaction
Pyrite Oxidation
Propagation
cycle
Degrades water quality > Mixing of
acid mine water into natural in river
Polluted water for human
consumption
Formation
of AMD and industrial use
• The breakdown of pyrite
– Leads to the formation of sulfuric acid and ferrous
iron
– pH values ranging from 2 to 4.5
– Sulfate ion concentrations ranging from 1,000 to
20,000 mg L−1 but a nondetectable ferrous iron
concentration
– The acid formed attack other minerals associated
with the coal and pyrite, causing breakdown of
rock fabric
• Alumunium : Highly toxic
• In AMD will be detectable some of acidophilic iron oxidizing thiobacilli.
Acidithiobacillus ferrooxidans is involved, pyrite biooxidation proceeds
• Pyrit Oxidation :
• Ferric ion oxidation
• Acidithiobacillus thiooxidans : Oxidized elemental sulfur (S0) and other
partially reduced sulfur species : Intermediates in pyrite oxidation to
sulfuric acid
• Metallogenium-like organism that they isolated from AMD ( Walsh and
Mitchell (1972) ) - pH drops below 3.5.
An early study by
Harrison (1978)
Microbial
succession
in coal spoil
under laboratory
conditions
Artificial coal spoil
Deposit into mound
d= 50 cm l= 25cm on
plastic tray
Absorbed
and migrated upward
Sampling
Inoculated : 20 L of an
emulsion of acid soil,
drainage water, and
mud from a spoil from
an old coal strip
mine
Initial
samples
:
After
8 weeks
:
The base of the
heterotrophs
were stillmound
dominant
BetweenHeterotrophic
12
bacteria.
and 20 weeks
:
The population
decreased
2 weeks : The
population
density of ∼107
cells g−1
Near the summit
of the mound,
pH values
• pH had dropped from 7 toHigher
5.
First 15 weeks :
Protozoans,
Heterotrophs
algae, and
• pH topredominated
just below 5 >> caused by aarthropod
burst of
growth by sulfur-oxidizing bacteria, >> then died
off progressively.
Acidithiobacillus
• The heterotrophic
again to
thiooxidans and population increased
Metallogenium
was not seen
Acidithiobacillus
just below
107 g−1.
ferrooxidans
8 weeks :
• TheAfter
sulfur-oxidizing
bacteria were assumed to be making use
heterotrophs
of elemental
sulfur resulting from the oxidation of pyrite by
were still
dominant
ferric
sulfate:
FeS2 +12Fe2(SO4)3
→ 3FeSO4 + 2S0
Between
and
Result...
20 weeks : The
population
decreased
NEW DISCOVERIES RELATING TO ACID MINE DRAINAGE
• A fairly recent study of abandoned mines at Iron Mountain,
California.
• The ore body at Iron Mountain
– various metal sulfides and was a source of Fe, Cu, Ag, and
Au.
– A signifi cant part of the iron was in the form of pyrite. The
drainage currently coming
• The distribution of Acidithiobacillus ferrooxidans and
Leptospirillum ferrooxidans from a pyrite deposit
– in the Richmond Mine, seepage from a tailings pile and
AMD storage tanks outside this mine
Acidithiobacillus
ferrooxidans
L. ferrooxidans
• Occurred in slime-based communities at
pH >1.3 at temperatures below 30°C
• Affect precipitation of ferric iron but
seemed to have
• a minor role in acid generation
• active role in generating ferric iron as an
oxidizing agent
• Abundant in subsurface slime-based
communities.
• Occurred in planktonic form at pH values
in the range of 0.3–0.7 between 30 and
50°C
• active role in generating ferric iron as an
oxidizing agent
• The Richmond Mine revealed the presence
of Archaea
• in summer and fall months: Archaea
represented ∼50% of the total population
• correlated these population fluctuations
with rainfall and conductivity, (dissolved
solids), pH, and temperature of the mine
water
• Ferroplasma acidarmanus, grew in slime
streamers on the pyrite surfaces.
• extremely acid-tolerant : pH optimum
at 1.2
• Its cells lack a wall
• Archaean order Thermoplasmales
Finally ...
SUMMARY
Summary
Require relatively
insoluble metal
compounds as
starting material to
limit the toxicity of
the metal ions to the
SRBs
Sulfate
H2S
Organic sulfur
compounds
Most nonferrous sulfides
Microbial role in biogenesis
of any sulfides deposits
(generation of H2S)
Demonstrated
in Lab
Abiogenically formed
(magmatic & hydrothermal processes)
Metal sulfides
Occur locally at
high concentration
A few sedimentary deposits
(some sedimentary ferrous sulfide
accumulation)
Relatively water insoluble
Biogenically formed
Spontaneous reaction of
metal ions with the biogenic sulfide
Ores
Summary
Direct oxidative attack
Microbial oxidation of
metal sulfides is
industrially exploited
Extracting metal values
(low-grade metal sulfide ore
and uraninite )
Has been tested successfully
on some high-grade ore and
ore concentrates
Pyrite oxidation in
bituminous coal seams
(mining activity)
AMD
Bacterial
action
subject to
oxidation
by bacteria
of the crystal lattice of a
metal sulfide
Indirect oxidative attack
by generation of lixiviant (acid
ferric sulfate), which oxidizes
the metal sulfide chemically
Solubilization of
uraninite (UO2)
Metal sulfides
Acidithiobacillus ferrooxidans
Leptospirillum ferrooxidans
Sulfolobus spp.
Acidianus brierleyi
others
End of Presentation. Any questions?
THANK YOU Ü