Many existing conceptual and mathematical models of
As part of a continuing study of contaminant distribution and metal sorption are derived from macroscopic measuretransport processes in aqueous environments, we have examined ments. X-ray absorption fine structure ( XAFS ) analysis is strontium sorption onto a hydrous ferric oxide (HFO). Samples one of a few techniques that can provide in situ structural of Sr sorbed to HFO were prepared by precipitation from ferric information about the sorbate and its surroundings. Brown nitrate solution and studied by XAFS spectroscopy. Sr K-edge ( 11 ) provides a comprehensive review of XAFS applicameasurements were performed with sample loadings from 10 01 to tions to environmental research. In XAFS, structural infor-1 mol Sr/mol Fe at 80 and 300 K. Analysis of the first coordination mation is obtained from variations in the absorption of Xshell clearly shows a beat at 8.0 A Λ01 . Good fits using the cumulant rays as a function of energy. The signal starts at the absorpexpansion to describe the distribution of oxygen were obtained, with approximately 10 oxygen atoms at 2.65 A Λ. No evidence was tion threshold and extends out to energies as high as about found for either Fe or Sr in the first shell. Second shell contribu-1 keV above the absorption edge. Signals from different tions of either Fe or Sr are evident in the data for Sr loaded at atomic species can be excited by tuning the X-ray energy 10 03 and 10 02 mol/g at both temperatures. For the Sr loading of to an absorption edge of the desired element; XAFS is 10 02 mol at 300 K, however, fits were obtainable only with Fe as element selective. the second neighbor. These results suggest that the Sr ion remains The high energy or extended XAFS regime, which is hydrated when sorbed to hydrated ferric oxide, indicating a physirelated to the wave properties of the electron, exists over cal type of adsorption. α§ 1998 Academic Press a range from approximately 40-to 1000-eV photoelectron