10.1021/es0522478.s001
Eugene S. Ilton
Eugene S.
Ilton
Steve M. Heald
Steve M.
Heald
Steven C. Smith
Steven C.
Smith
David Elbert
David
Elbert
Chongxuan Liu
Chongxuan
Liu
Reduction of Uranyl in the Interlayer
Region of Low Iron Micas under
Anoxic and Aerobic Conditions
American Chemical Society
2006
peak U concentrations
U diffusion profiles
FeII
UVI
Aerobic ConditionsThe role
mica
Low Iron Micas
XANES
anoxic conditions
2006-08-15 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Reduction_of_Uranyl_in_the_Interlayer_Region_of_Low_Iron_Micas_under_Anoxic_and_Aerobic_Conditions/3065194
The role of the interlayer region of three different Fe<sup>II</sup>-poor micas (2.8, ∼0.02, and 0.01 Fe<sup>II</sup> atom %) in the reduction
of U<sup>VI</sup> was investigated at pH ∼4.3, low ionic strength,
and 23 °C under both anoxic and aerated conditions in batch
reactors for 1 to 10 days. U diffusion profiles were
mapped with X-ray microscopy, and the oxidation state of
U was tracked with XANES as a function of distance
from the crystal edge. Peak U concentrations only reached
about 0.006−0.0002 atom percent, where the full-width-at-half-maximums of the diffusion fronts were roughly 25−50 μm. Results for anoxic conditions indicated appreciable
reduction of uranyl in all three micas with no measurable
dependency on distance from the edge. Under aerobic
(open to the atmosphere) conditions, U was still partially
reduced, although to a lesser degree than for anoxic
conditions, and U<sup>VI</sup>/U<sub>tot</sub> increased with time. Interestingly,
reoxidation reached a plateau after about 3−10 days,
leaving an appreciable proportion of U reduced. It is likely
that measurable reduction occurred, despite low Fe<sup>II</sup>,
because U concentrations were even lower, where Fe<sup>II</sup>/U
ratios ranged from about 10<sup>4</sup>−10<sup>2</sup>. A coupled diffusion-reduction model was developed that successfully simulated
the proximal portion of the diffusion front. The results
show that reduction of U<sup>VI</sup> in the interlayer of low Fe<sup>II</sup> micas
is, in principle, viable and that under aerobic conditions
reduction is initially faster than reoxidation. This extends the
range of possible environments where heterogeneous
reduction of U<sup>VI</sup> by micas might occur.