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COBALT METAL FACTS
Cobalt (Co) is one of the most essential
elements for the humankind. It has several strategic
and irreplaceable industrial applications. It
is a silvery metal with close packed hexagonal
crystal structure. Its common properties are as
follows:
Density = 8.85 g/cm3, Melting point
= 1493°C, Boiling point = 3100°C
Atomic number = 27, Valency = +2 & +3
Co has the property of retaining its strength
even at very high temperatures, and hence is used
extensively in superalloys, surface coatings,
high-speed steel, high-temperature cutting tools,
cemented carbides etc.
Co can retain ferromagnetic property up to a
temperature of 1100°C, which is highest for
any other metals. Therefore, it is used in manufacturing
of Alnico magnets, recording tapes, soft magnetic
material, alloys for spacecraft etc.
Co in conjunction with silica produces intense
deep blue colour and hence is used in manufacturing
of paints and enamels.
Co as acetate is an effective catalyst, hence
extensively used in oil refineries. Apart from
these usages Co is finding increasing application
in electronic industry.
Co is 33rd abundant metal in the earth's crust
but is highly scattered. Exploitable concentration
is found in several countries, out of which, 17
countries presently produce this metal either
from its own land resources (12 countries) or
by refining imported slag and scrap (5 countries).
Co is mostly associated with copper, nickel, and
arsenic ores. In 2003 nearly 40 % of the world
production came from nickel ores. Presently the
world production of Co stands at around 42000
tonnes, and current land deposits are estimated
to last for over 100 years. Co mining is active
in Australia, Brazil, Belgium, Canada, China,
Cuba, Morocco, Zambia, South Africa. India is
one of the countries that refined nearly 500 tonnes
of Co during 2004 from imported slag concentrates
from Congo and Cuba. In most of the cases Co is
produced as byproduct of Ni and Cu mining. The
pure (99.8 %) Co metal price rose to as high as
~28 $ per lb (60 $ / Kg) in recent past and is
again low at ~US$ 15/lb (Source: www.thecdi.com
), but the price is highly variable. In view of
the importance of cobalt metals we felt it worth
exploring marine regime for the cobalt-deposits.
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Team Members:
Dr.
Rajiv Nigam
Dr.
Abhay Mudholkar
Sh.
G. Parthiban
Sh. R. Manimurali
Sh.
D. Gracias
Dr. Anjali Chodankar
Ms. Rajani Ramesh
Sh. Sanjay Rana
Dr.
N. B. Bhosle
Dr.
P. A. Loka Bharati
Dr.
N. Ramaiah
Sh. K. P. Krishnan
Ms. Ranjita Harji
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WHAT ARE THESE DEPOSITS
Ferromanganese encrustations (Fe-Mn Crust) containing
on an average >1% of cobalt metal can be designated
as Co-rich crust. The Co-rich crusts accrete at
shallow water depth (generally <2500 m) as
slabs capping the seamounts. They are 3-6 times
more enriched in Cobalt metal than the abyssal
polymetallic nodules and deep-water crusts. Ferromanganese
crusts are hydrogenous colloidal precipitates,
which are known to record oceanographic conditions
contemporaneous to their growth period. The Co-rich
crusts are purely hydrogenetic precipitates, wherein
the cobalt concentration was shown to relate inversely
with their growth rate. The primary requirements
for Co-rich crust formation are:
a) Availability of sediment free hard substrate
b) Fairly oxic ambient water
c) Large supply of oxidizable Mn
Such conditions are generally found on seamounts
rising in to the OMZ, where a large supply of
dissolved Mn can be expected due to intense oxidation
of the organic matter. In the water column the
Mn- and Fe-oxides occur together as colloidal
flocks. Below the OMZ (generally below 1000 m
depth in northern Indian Ocean) oxidizable-Mn
availability is large and hence, the crusts forming
at this depth enrich mangalophile elements like
Mn, Co, Pb etc. Cobalt and other metals are fixed
by lattice substitution for Mn4+ in the MnO2.
Another pathway of Cobalt enrichment is due to
its ability to oxidise on the surfaces of MnO2
colloids to Co3+, which is less soluble and more
stable than other minor metals. This is the reason
why the seamount ferromanganese crusts formed
closer to OMZ tend to enrich cobalt over other
transition metals. It is also worth noting here
that the Co-rich crusts do concentrate platinum
(up to 2.5 ppm) compared to deep-water Fe-Mn nodules.
Therefore, the seamount ferromanganese crusts
have attracted the attention of mineral explorers.
The Fe-Mn crusts cap most of the shallow-water
seamounts in the world oceans. The seamount Fe-Mn
crusts deposited in inactive-hydrothermal regions
are exclusively of hydrogenetic origin because
of non-availability of diagenetically remobilized
metals due to sediment starvation. Most of the
transition- and alkali-metals are preferentially
removed from the ambient water by adsorption on
to the negatively charged surfaces of MnO2 colloids,
while negatively charged ions preferentially bind
to the slight positively charged FeOOH phase during
the Fe-Mn crust formation. Hydrogenous Fe-Mn crusts
accumulate by slow accretion (<10 mm/ Ma) of
Fe-Mn oxyhydroxides precipitated from the ambient
seawater. The slow growth rate allows for effective
adsorption of considerable quantity of minor elements
by the oxyhydroxide colloids during the process
of Fe-Mn crust accretion. The Fe-hydroxide precipitate
forms the beginning layer during the hydrogenetic
accretion of the crust oxide, which subsequently
catalyses the oxidation of Mn. The further growth
process of the Fe-Mn crusts is believed to be
autocatalytic. The dominant controls on the concentrations
of elements in the Fe-Mn crusts include the concentrations
of metals in seawater, surface-charge and -area
of the colloidal particles, and growth rate.
The seamount Fe-Mn crusts exhibit enrichment
of metals over the seawater composition by several
orders and most dominantly enriched metal species
are the transition group comprising Mn, Fe, Co,
Ni, Cu, V, Pb, Zn, etc. The second group of elements
that is enriched is the REE and followed by ultra-trace
metal such as platinum group metals. Although
considerable work has been done on the Fe-Mn crusts
of the world oceans, the studies on Indian Ocean
Fe-Mn crusts are limited. Particularly the studies
on ANS Fe-Mn crust are extremely sparse and were
based on samples collected from a single dredging-operation
in the upper flank of the ANS (see Banakar et
al. 1997, Marine Geology; Parthiban and Banakar,
1999, Indian Mineralogist).
Exploring for new mineral deposits generally
depends on its utility, cost, and availability
on the land. As far as India is concerned, no
workable deposits of cobalt have been located.
Low-grade non-workable deposits of Co have been
reported from Singbhum district of Bihar. According
to Cobalt Development Institute cobalt-metal market
is extremely complex and volatile. Hence, the
economics of the Cobalt-Crust mining and metallurgy
requires expert opinions, and is out of the scope
of present information.
EVOLUTION OF THE PROJECT
Subsequent to the first recovery of cobalt-enriched
Ferromanganese Crusts in 1994 from the Afanasiy-Nikitin
Seamount (ANS) on board RV. Sidorenko (See Banakar
et al., 1997, Marine Geology), the National Institute
of Oceanography initiated in-house R & D Project.
The samples for this R & D project were collected
on board R.V. A.A. Sidorenko. We conducted only
one dredging operation on the ANS at 3°S Latitude
& 83°E Longitude in the Equatorial Indian
Ocean, which yielded nearly 70 kilograms of samples.
The samples were mainly composed of Fe-Mn oxide
deposits on hard carbonate substrates with cobalt
content up to 0.8 %. The detailed physical and
chemical description, and potential of those samples
as indicators of palaeoceanographic conditions
have been reported in Banakar et al (1997). We
have traced some interesting palaeoceanographic
changes such as, major drop in global sea level
during the Oligocene, lowering of oxygen content
in the intermediate depths in the region during
Late Miocene, and signatures of intensified Himalayan
erosion at the close of Miocene.
After the first-time recovery of cobalt enriched
ferromanganese crusts from the ANS, we proposed
a project to DOD for funding, which received funding
for X 5-Year Plan period. The Indian western-EEZ
also hosts several small seamounts, which were
also thought to provide interesting sites for
cobalt-crust exploration. Thus exploring the cobalt-crusts
on the Indian Ocean seamounts (particularly ANS
and Indian EEZ-Seamounts) was the main objective
of the submitted proposal. However, we have built-in
R & D program with the main exploration objective,
as we felt that the samples to be collected potentially
contain valuable clues on past oceanographic changes.
Additionally, collecting possible water column
data to provide some baseline environmental parameters
and to understand equatorial water biogeochemistry
were also incorporated in the project. Thus the
evolved project is multidisciplinary in nature.
The ANS in Equatorial East Indian Ocean (EEIO)
was discovered during the RV. Vityaz cruise of
1959 by Russian scientists, and was shown to have
formed during the Late-Cretaceous. The ANS has
evolved as a part of 85° E Ridge. Although,
the Russian researchers have extensively explored
this seamount with the help of 'Mir' submersible,
the cobalt-enriched ferromanganese crusts were
discovered only during 1994, onboard R.V.Sidorenko
by NIO scientists. Subsequent to its emplacement
the ANS has undergone tectonic disturbances due
to intraplate deformation episodes in the region
as evidenced by numerous criss-cross faulting
of the seamount. The seamounts in Laxmi Basin
(western EEZ of India) viz. Raman Seamount, Panikker
Seamount, and Wadiya Guyot have been previously
mapped by the multibeam and details are available
in Bhattacharrya et al., (1994, Marine Geodesy).
Although the sedimentation rate in this region
is very high, the occurrence of Fe-Mn crusts may
be expected because of very strong OMZ in the
overlying water. Further, the samples (rocks and
Fe-Mn crusts) from these seamounts may hold important
evidences to address their controversial origin.
Few locations on the Lakshadweep Ridge were also
considered for sampling.
Afanasiy-Nikitin Seamounts in Equatorial Indian
Ocean
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Some specimen of cobalt-enriched Fe-Mn crusts
from the Afanasiy-Nikitin Seamounts in the
Equatorial Indian Ocean |
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