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

Abstract

The sorption behavior is studied and the physicochemical neptunium species existing on the surface of goethite (α-FeOOH), maghemite (γ-Fe2O3), and hematite (α-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 NpO 2 + 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 α-FeOOH, γ-Fe2O3, and α-Fe2O3. Presumably, the oxygen atoms of iron oxides and water and/or carbonate (CO 3 2- ) or nitrate (NO 3 - ) group lie in the equatorial plane of the neptunyl (NpO 2 + ) group.