Micro-XAS studies with sorbed plutonium on tuff

The bonding environment of sorbed species at rock-water interfaces provides information on their mobility in natural systems. To investigate Pu sorpti on at a natural surface on a microscopic scale, we studied the bonding envi ronment of sorbed Pu on zeolitic tuff with micro-XAS techniques. Using a fo cused 4 by 7 mu m(2) beam, XAS spectra were taken at Mn-smectite regions wh ere high levels of sorbed Pu were found. The Pu did not sorb to Fe-rich reg ions. XANES spectra show the presence of Pu(VI), based on edge energy. Prel iminary analyses of the micro-EXAFS spectra indicate the absence of a first shell splitting of axial and equatorial Pu-O bonds-an environment unlike w hat is observed for most hexavalent actinides.