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.