An XAFS analysis of strontium at the hydrous ferric oxide surface

As part of a continuing study of contaminant distribution and transport processes in aqueous environments, we have examined strontium sorption onto a hydrous ferric oxide (HFO). Samples of Sr sorbed to HFO were prepared by precipitation from ferric nitrate solution and studied by XAFS spectroscopy. Sr K-edge measurements were performed with sample loadings from 10(-1) to 1 mol Sr/mol Fe at 80 and 300 K. Analysis of the first coordination shell clearly shows a beat at 8.0 Angstrom(-1). Good fits using the cumulant expansion to describe the distribution of oxygen were obtained, with approximately 10 oxygen atoms at 2.65 Angstrom. No evidence was found for either Fe or Sr in the first shell. Second shell contributions of either Fe or Sr are evident in the data for Sr loaded at 10(-3) and 10(-2) mol/g at both temperatures. For the Sr loading of 10(-2) mol at 300 K, however, fits were obtainable only with Fe as the second neighbor. These results suggest that the Sr ion remains hydrated when sorbed to hydrated ferric oxide, indicating a physical type of adsorption. (C) 1998 Academic Press.