Mica Surfaces Stabilize Pentavalent Uranium

High-resolution X-ray photoelectron spectroscopy was used to demonstrate that reduction of aqueous U⁶⁺ at ferrous mica surfaces at 25 °C preserves U⁵⁺ as the dominant sorbed species over a broad range of solution compositions. Polymerization of sorbed U⁵⁺ with sorbed U⁶⁺ and U⁴⁺ is identified as a possible mechanism for how mineral surfaces circumvent the rapid disproportionation of aqueous U⁵⁺. The general nature of this mechanism suggests that U⁵⁺ could play an important, but previously unidentified, role in the low-temperature chemistry of uranium in reducing, heterogeneous aqueous systems.