Interaction of neptunyl with goethite (α-FeOOH), maghemite (γ-Fe2O3), and hematite (α-Fe2O3) in water as probed by X-ray photoelectron spectroscopy

The sorption behavior is studied and the physicochemical neptunium species existing on the surface of goethite (alpha-FeOOH), maghemite (gamma-Fe2O3), and hematite (alpha-Fe2O3) are determined. Solvent extraction and X-ray photoelectron spectroscopy (XPS) are used to determine the neptunium surface species. The ion and elemental composition of the surface of the minerals and surface neptunyl NpO2+ complexes is determined using these data. Compounds containing neptunium(IV) or neptunium(VI) ions do not appear; rather, neptunyl (Np(V)O-2(+)) group is complexed with surface hydroxide groups of alpha-FeOOH, gamma-Fe2O3, and alpha-Fe2O3. Presumably, the oxygen atoms of iron oxides and water and/ or carbonate (CO32-) or nitrate (NO3-) group lie in the equatorial plane of the neptunyl (NpO2+) group.