Technologies to harvest uranium from sea
K.S. PARTHASARATHY
Uranium in trace quantities is present in soil, rock and water.
Bounteous nature leaves about 4.5 billion tonnes of uranium in sea
water, a thousand times more than what is known to exist in uranium
mines. Since its concentration is extremely low (only one particle of
uranium for 34 million particles of other elements), harvesting uranium
from sea is a formidable task.
Japan developed a technology by using plastic sheets to which
amidoxime, which is capable of selectively absorbing uranium from
seawater, is grafted by high energy electron beam irradiation.
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Uranium |
Scientists from the Desalination Division, Bhabha Atomic Research
Centre recovered uranium at milligram levels from sea water using
electron beam grafted amidoxime.
They developed a semi pilot scale facility to produce radiation
grafted sheets of 1 metre X 1 metre size.
They collected about 800 microgrammes of uranium in five campaigns
from CIRUS Jettyhead; about 1.8 milligrams from the seawater intake and
outfall canals at the Tarapur Atomic Power Station and around 200
microgrammes from Andaman and Nicobar Islands. Though these amounts are
trivial, it gives confidence in the technology
Field trials carried out at the three locations gave concentration
factors of 300, 600 and 700 for the submergence of the absorbent
material for 12, 14 and 23 days respectively.
"What are the reasons for obtaining different concentration factors
at different locations?" "The concentration factor depends on corrosion,
bio-fouling and their combined effect on the adsorption kinetics. These
may be different at different locations," Dr P.K. Tewari, Head,
Desalination Division, BARC responded to my query.
BARC scientists studied these factors and the mechanical properties
of the materials used in the suspension assembly and the substrate. They
established their compatibilities with seawater and process chemicals
and the optimum submergence periods for various locations. They also
evaluated the potential of Polyhydroxamic Acid (PHOA) sorbent, for
uptake of uranium from seawater. They obtained a concentration factor of
over 190, when the resin, filled in a porous bag was dipped in seawater
for a period ranging from 10-30 days.
BARC and the Commissariat a' Energie Atomique (CEA), France, are
collaborating to develop three innovative and efficient methods of
uranium extraction from the concentrated brine rejected by integrated
nuclear desalination systems, which both partners are currently
developing.
The first method uses resin-grafted with calixarene (a synthetic
material, indecently expensive!); magnetic separation is the second
method and the third uses a canal system using absorbents.
These methods are highly selective but need further research and
development.
Using three absorption cages, each of cross sectional area of 16
square metres and height of 16 cm and consisting of stacks of 52,000
uranium specific, non-woven sheets with a total mass of 350 kg, a
Japanese group recovered more than one kg of uranium in terms of yellow
cake during a submersion period of 240 days in the ocean.
(Courtesy: The Hindu) |
