title: Inhibition of U(VI) reduction by synthetic and natural pyrite.
abstract: Reductive precipitation is an effective method of attenuating the mobility of uranium (U) in subsurface environments. The reduction of U(VI) by synthetic and naturally occurring pyrite was investigated at pH 3.0-9.5. In contrast to thermodynamic calculations that were used to predict UO2(s) precipitation, a mixed U(IV) and U(VI) product (e.g., U3O8/U4O9/U3O7) was only observed at pH 6.21-8.63 and 4.52-4.83 for synthetic and natural pyrite, respectively. Under acidic conditions, the reduction of UO2(2+) by surface-associated Fe(2+) may not be favored because the mineral surface is nearly neutral or not negative enough. At high pH, the sorption of negatively charged U(VI) species is not favored on the negatively charged mineral surface. Thus, the redox reaction is not favored. Trace elements generally contained within the natural pyrite structure can affect the reactivity of pyrite and lead to a different result between the natural and synthetic pyrite. Because UO2(s) is extremely redox-sensitive toward U(VI), the observed UO2+x(s) phase reduction product indicates a surface reaction that is largely controlled by reaction kinetics and pyrite surface chemistry. These factors may explain why most laboratory experiments have observed incomplete U(VI) reduction on Fe(II)-bearing minerals.
authors.affiliation: Beijing National Laboratory for Molecular Sciences, Fundamental Science Laboratory on Radiochemistry & Radiation Chemistry, College of Chemistry and Molecular Engineering, Peking University , Beijing, 100871, China.
authors.forename: Zhuanwei
authors.initials: Z
authors.lastname: Yang
authors.forename: Mingliang
authors.initials: M
authors.lastname: Kang
authors.forename: Bin
authors.initials: B
authors.lastname: Ma
authors.forename: Jinglin
authors.initials: J
authors.lastname: Xie
authors.forename: Fanrong
authors.initials: F
authors.lastname: Chen
authors.forename: Laurent
authors.initials: L
authors.lastname: Charlet
authors.forename: Chunli
authors.initials: C
authors.lastname: Liu
mesh_terms: D007501:Iron / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D010084:Oxidation-Reduction; D056951:Photoelectron Spectroscopy; D012996:Solutions; D013440:Sulfides / Q000737:chemistry*; D013816:Thermodynamics; D014501:Uranium / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D012996:Solutions; D013440:Sulfides; D014867:Water; C011342:pyrite; D014501:Uranium; D007501:Iron