Uranium(VI) interaction with pyrite (FeS₂): Chemical and spectroscopic studies

Abstract

The mechanism of uranium(VI) interaction with pyrite was studied by solution chemistry and X-ray Photoelectron Spectroscopy (XPS). Natural pyrite was characterized by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). After equilibration in 10 -2 mol L -1 NaNO 3 , pyrite was reacted with uranium(VI) by the batch method in an anoxic glove box (P O 2 <1 ppm) at ambient temperature. The reaction products of uranium, iron and sulphur were characterized (oxidation state, chemical environment) by XPS. Quantitative analysis revealed that only a few atomic percent of uranium is retained at the pyrite surface. The U4 f core level binding energies are consistent with the coexistence of an uranium(VI) species and of uranium in a reduced form. No sulphur oxidation products were observed by XPS, but spectral decomposition of the Fe2 p lines revealed the presence of iron(III) oxide or (oxy)hydroxide. These results seem to point to a redox reaction between uranium(VI) and pyrite.