X-ray absorption studies of uranium sorption on mineral substrates

Uranium L{sub 3}-edge x-ray absorption spectra have been measured for uranium-mineral sorption systems. An expansible layer silicate, vermiculite, was treated to obtain a collapsed and non-expanding phase, thereby limiting access to the interior cation exchange sites. Samples were prepared by exposing the finely powdered mineral, in the natural and modified form, to aqueous solutions of uranyl chloride. EXAFS spectra of the encapsulated samples were measured at the Stanford Synchrotron Radiation Laboratory. Results indicate that the uranyl ion possesses a more symmetric local structure within the interlayer regions of vermiculite than on the external surfaces