Fractionation of clay colloids and their synthetic utility in vanadium hydroxide-clay thin film formation.

Stable mineral colloids play a role in the mobilization of actinide contaminants in the environment. In this paper we present a method to isolate and identify colloids released from high surface area sorbents associated with a proposed clay mineral barrier in a nuclear waste repository. The mineral colloids, which have a strong tendency to remain dispersed in solution, were separated from Al 13 - or (Ce Al)-pillared clay sediment, adsorbed on glass together with hydrolyzed vanadium(IV) species and studied by a variety of techniques including grazing-incidence X-ray scattering (GIXS), small-angle X-ray scattering (SAXS), Fourier transform-infrared spectroscopy (FT-IR) and atomic force microscopy (AFM). We show that the clay platelets are dimensionally orientated in the continuous, transparent 100 nm thick film until the onset of vanadium oxides above 350 °C. Organic matter and the secondary mineral quartz limit the swelling capacity of the platelets, an indication that the stable colloids originate from a part of the native clay that could not be intercalated by aluminum cations. X-ray scattering from oriented clay films intercalated by aluminum- and mixed cerium/aluminum oxo-hydroxy cations are also investigated by the GIXS technique. Unlabelled Image • A continuous, vanadium hydroxide/clay-colloid thin film was self-assembled on glass. • Clay nanoplates dimensionally orient within the 100 nm thick film. • Platelet orientation is preserved until the onset of vanadium oxides above 350 °C. • The platelets are potentially useful for actinide/clay-colloid transport studies. [ABSTRACT FROM AUTHOR]