Aluminum oxy-hydroxide phases readily occur in nature and are important in industrial processing scenarios.  With respect to nuclear materials processing, significant amounts of Al may end up in high-level nuclear waste streams from the dissolution of fuel cladding.  In the case of the Hanford Site (Washinigton State, USA), Al was also added to waste streams to increase ionic strength during processing and to minimize the corrosion of steel holding tanks.  Over many decades of storage in the presence of numerous metals, organic and inorganic solvents, and radiation fields, gibbsite (Al(OH)<sub>3</sub>) became a dominant precipitate.  Subsequent exposure to elevated temperatures due to heat from radioactive decay led to the transformation of gibbsite to boehmite (γ-AlOOH) in certain waste tanks.  Outstanding questions remain, however, regarding the association of trace metals (e.g., Cr, Fe, Mn, and U) with both phases as they are observed to affect the dissolution behavior of boehmite in particular.  To mimic experimental conditions for the formation of boehmite, atomic scale modeling was used to simulate Cr(III) incorporation into the gibbsite structure as one possible pathway to Cr association with boehmite (e.g., a gibbsite to boehmite dehydration step under alkaline conditions).  The calculated energy barriers to Cr incorporation into gibbsite support experimental and theoretical results pointing towards a preference for surface association of Cr with boehmite.  Comparisons are made with other trace metals where preference for surface versus bulk incorporation has implication for aluminum oxyhydroxide dissolution behavior.<br/>

Fate of trace metals during aluminum oxyhydroxide phase transitions: Implications for reactivity

253rd National Meeting (2017)

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