Chemistry Reference
In-Depth Information
Table 1.
Some biologically-induced
iron and manganese minerals
Chemical Formula
Mineral Name
Fe(OH)
3
(approx.)
Ferric oxyhydroxide
2
Fe(OH)
3
·Fe(OH)
2
(approx.)
Green rust
α
-FeO(OH)
Goethite
γ
-FEO(OH)
Lepidocrocite
5Fe
2
O
3
·9H
2
O
Ferrihydrite
Fe
3
O
4
Magnetite
γ
-Fe
2
O
3
Maghemite
FeCO
3
Siderite
FePO
4
·nH
2
O Hydrous Ferric Phosphate
Fe
3
(PO
4
)
2
·2H
2
O Vivianite
FeS Cubic FeS (Sphalerite-type)
FeS Mackinawite (tetragonal FeS)
Fe
3
S
4
Greigite
Fe
1-x
S Pyrrhotite
FeS
2
Pyrite
KFe
3
(SO
4
)
2
(OH)
6
Jarosite
Fe
8
O
8
SO
4
(OH)
6
Schwertmanite
FeSO
4
·7H
2
O Melanterite
MnCO
3
Rhodochrosite
Mn
4
O
7
·H
2
O Todorokite
Na
4
Mn
14
O
27
·9H
2
O Birnessite
Adapted from Lowenstam and Weiner 1989.
Iron and manganese oxidation
Fe- and Mn-oxidizing bacteria are known to be responsible for the precipitation of
oxides of both metals at acidic and neutral pH conditions. At low pH, where oxidized
Fe(III) and Mn(IV) are soluble, active mineralization by organisms, such as the
mesophilic, autotrophic Bacteria
Acidithiobacillus ferrooxidans
(formerly
Thiobacillus
ferrooxidans
) (Kelly and Wood 2000) or
Leptospirillum
spp., that oxidize Fe(II), may be
more important in iron oxyhydroxide precipitation (Fortin and Beveridge 2000; Southam
2000). The acidophiles are better known for their dissolution and bioleaching of minerals,
particularly sulfide minerals such as pyrite, but are often involved in the nucleation and
deposition of a secondary mineral, ferric oxyhydroxide, during Fe(II) oxidation (Fig. 2).
Although mineral formation by BIM processes may not have been definitively
demonstrated in every case, all Fe(II) oxidizers should be considered to have this
potential. The known Fe(II)-oxidizing acidophiles are diverse and include: thermotolerant
gram-positive species such as
Sulfobacillus
spp.,
Acidimicrobium ferrooxidans
, and
Ferromicrobium acidophilus
(Blake and Johnson 2000); mesophilic Archaea such as
Ferroplasma
spp. (Edwards et al. 2000, 2001; Golyshina et al. 2000) that lack cell walls;
and thermophilic Archaea such as
Sulfolobus
spp.,
Acidianus brierleyi
,
Metallosphaera
spp., and
Sulfurococcus yellowstonensis
(Blake and Johnson 2000).
