A KINETIC-STUDY OF CATION RELEASE FROM A MIXED MINERAL ASSEMBLAGE - IMPLICATIONS FOR DETERMINATION OF URANIUM UPTAKE

The uptake of U(VI) as UO22+ on a natural complex mineral assemblage h as been studied using batch selective chemical extraction techniques a nd secondary ion mass spectroscopy (SIMS). Sediments used in the study consisted of a quartz/mica schist collected from the locale of the Ko ongarra Uranium ore body, Alligator Rivers Uranium Province, Northern Territory, Australia. The bulk sediment was gravity separated into fou r size fractions, with attention focused on the nominally <25 mu m and 250-1000 mu m fractions of the bulk sample, in order to assess the ef fects of particle size on uranium uptake. Investigation of the kinetic s of elemental release in the presence of selective extractants show t hat uranium is bound largely within the iron and aluminium oxyhydroxid es of the assemblage, with a highly mobile fraction of this associated with aluminol sites. SIMS analysis of the natural substrate confirms that significant quantities of aluminium are present in surface layers . The effect of particle size on the uptake of uranium indicates very Little change with respect to particle size. This finding may be attri buted to the presence of highly porous surface coatings.