Sunday, 4 August 2013

Sulfide and iron work together to reveal a new path for radionuclide sequestration

Sulfide and iron work together to
reveal a new path for radionuclide
Sifting radionuclides with sulfur:
Technetium sequestration pathways
under sulfidogenic conditions
stimulated by nZVI offer a possibly
more sustainable, environmentally
friendly approach to bioremediation.
As an ongoing concern for the
Department of Energy's Office of
Biological and Environmental
Research (DOE-BER), bioremediation
strategies that either remove
contaminants or retard their mobility
in the environment are long-sought-
after solutions. Technetium-99, an
isotope generated from nuclear
fission stemming from Manhattan
Project-era plutonium processing, is
among the high-priority radionuclides
requiring environmental controls.
In one approach to tackle this
problem, scientists measured
reduction of soluble pertechnetate
(99 TcO4 ?) by nano zerovalent iron
(nZVI) that had been pre-exposed to
sulfide (S 2- ) in simulated Hanford
Site groundwater. nZVI promotes
microbial reduction of sulfate (SO 4 2- )
to S 2- and offers a promising and
sustainable method for generating
S 2- in the environment.
Their work, using a mix of
microscopy-, diffraction-, and
spectroscopy-aided assessments and
conceptual modeling, was designed to
provide a fundamental geochemical
understanding of Tc sequestration as
new sulfide compounds developed in
the presence of nZVI, as well as offer
an alternative remediation strategy.
The scientists examined the evolution
of mineral phases during the
changing sulfidation states using a
mix of EMSL's capabilities and X-ray
absorption spectroscopy (XAS) at the
Stanford Synchrotron Radiation
Lightsource (SSRL).
They coupled this work to Tc
sequestration kinetics under
incremental sulfur/iron ratios. Their
results showed the importance of
iron sulfide in Tc sequestration and
how sulfidation of nZVI can direct
TcO4 ? sequestration products from Tc
(IV) oxide—which is highly
susceptible to reoxidation—to Tc(IV)
sulfide phases, providing a more
favorable sequestration pathway.
More information: Fan, D. et al.
2013. Reductive Sequestration of
Pertechnetate ( 99 TcO4 –) by Nano
Zerovalent Iron (nZVI) Transformed
by Abiotic Sulfide, Environmental
Science & Technology 47(10)
:5302-5310. DOI: 10.1021/es304829z .
Provided by Environmental Molecular
Sciences Laboratory

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