title: Reduction of U(VI) incorporated in the structure of hematite.
abstract: U(VI) doped hematite was synthesized and exposed to two different organic reductants with E(0) of 0.23 and 0.70 V. A combination of HAADF-TEM and EXAFS provided evidence that uranium was incorporated in hematite in uranate, likely octahedral coordination. XPS indicated that structurally incorporated U(VI) was reduced to U(V), whereas non-incorporated U(VI) was reduced to U(IV). Specifically, the experiments indicate that U(V) was the dominant oxidation state of uranium in hematite around Eh -0.24 to -0.28 V and pH 7.7-8.6 for at least up to 5 weeks of reaction time. U(V), but not U(IV), was also detected in hematite at Eh +0.21 V (pH 7.1-7.3). The results support the hypothesis, based on previous experimental and theoretical work, that the stability field of U(V) is widened relative to U(IV) and U(VI) in uranate coordination environments where the coordination number of U is less than 8.
authors: Pacific Northwest National Laboratory, Richland, Washington 99352, United States. Eugene.Ilton@pnnl.gov
authors: Eugene S
authors: ES
authors: Ilton
authors: Juan S Lezama
authors: JS
authors: Pacheco
authors: John R
authors: JR
authors: Bargar
authors: Zhi
authors: Z
authors: Shi
authors: Juan
authors: J
authors: Liu
authors: Libor
authors: L
authors: Kovarik
authors: Mark H
authors: MH
authors: Engelhard
authors: Andrew R
authors: AR
authors: Felmy
mesh_terms: D005290:Ferric Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D014501:Uranium / Q000737:chemistry*; D017974:Uranium Compounds / Q000737:chemistry
chemical_list: D005290:Ferric Compounds; D017974:Uranium Compounds; C000499:ferric oxide; D014501:Uranium