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 degrees 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.