Boehmite (γ-AlOOH) and gibbsite (α-Al(OH)<sub>3</sub>) are important archetype (oxy)hydroxides of aluminum in nature that also play diverse roles across a plethora of industrial applications.  As a consequence, highly precise synthesis of these pure phases with controlled particle size, shape and properties towards an end of tunable chemical behavior is an important ongoing research and development enterprise. In addition, they are prominent components in high-level nuclear waste stored in large quantities at the Hanford Site, Washington with future processing plans dependent on developing a predictive understanding of crystal growth of these two materials. However, mechanisms of crystal growth of these minerals still remain poorly understood, particularly in the complex environment of concentrated sodium hydroxide at low water activity. In this work, magic angle spinning nuclear magnetic resonance (MAS-NMR), high resolution atomic force microscopy (AFM), scanning electron microscopy (SEM),  transmission electron microscopy (TEM), Raman, X-ray absorption spectroscopy (XAS), high resolution powder X-ray diffraction (XRD), and X-ray Pair Distribution Function (PDF) techniques were conducted to investigate the crystallization of gibbsite and boehmite nanocrystals. By focusing on understanding the role of aluminum coordination change dynamics from tetrahedral in solution to octahedral in solids and vice versa, and the intermediate pentacoordinate state, some unifying principles governing these transformation emerge, which are of importance for developing new methods to morphology and size controlled synthesis of boehmite and gibbsite nanocrystals and also are critical to proposal reliable techniques to manage the aluminum based minerals in nuclear waste.

Probing crystal growth of gibbsite and boehmite nanocrystals

2019 Spring National Meeting

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