Adsorption to iron(oxyhydr)oxide minerals such as goethite (alpha-FeOO
H) may be an important retardation factor for the mobility of Sr-90 fr
om radioactive waste repositories. EXAFS spectroscopy was used here to
examine the coordination sphere around Sr2+ sorbed to goethite at pH
9.2 and 10.2. At both pHs studied, Sr was found to be coordinated to 8
.0 +/- 10 atoms at a distance of 2.61 +/- 0.02. At pH 10.2, a further
coordination sphere of 1.8 +/- 0.5 Fe atoms at 4.29 +/- 0.02 Angstrom
demonstrated that Sr was adsorbed to goethite by an inner-sphere mecha
nism. From the EXAFS data, the crystallographic structure and morpholo
gy of goethite, it is proposed that the inner-sphere coordination of S
r is via two oxygen atoms (A-type hydroxyls) bound to adjacent Fe(III)
) atoms on the dominant (110) surface of goethite. This is the first s
tudy of Sr sorption to an (oxyhydr)oxide mineral at an atomistic level
.