Preferential association of adsorbed uranium with mineral surfaces: a study using analytical electron microscopy

Abstract

Analytical electron microscopy (AEM) has been employed to characterize the distribution of U(VI) on several mineral substrates, including standard kaolinite samples and weathered rock samples from Koongarra, Australia. Results of this study reveal that pre-existing impurity phases play a significant role in the uptake of U(VI) on standard kaolinite samples. Using a natural sample from the weathered zone of the Koongarra uranium deposit, we have also demonstrated that U(VI) sorption is controlled by iron oxyhydroxides (predominantly goethite) which constitute a small fraction of the sample. Limited sorption of U(VI) was observed on the clay minerals of this substrate. Uptake of U(VI) by goethite increases with total uranium content up to the point of uranium precipitation, after which it decreases dramatically. Uranium precipitation is indicated by the appearance of a uranyl oxyhydroxide phase. © 1999 Materials Research Society