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pH dependence of uranyl retention in a quartz/solution system: an XPS study

Abstract : We have investigated the pH dependence of U(VI) retention in quartz/10^{−4} M uranyl solution systems, under conditions favoring formation of polynuclear aqueous species and of colloids of amorphous schoepite as U(VI) solubility-limiting phases. X-ray photoelectron spectroscopy was used to gain insights into the coordination environments of sorbed/precipitated uranyl ions in the centrifuged quartz samples. The U4f XPS spectra made it possible to identify unambiguously the presence of two uranyl components. A high binding energy component, whose relative proportion increases with pH, exhibits the U4f lines characteristic of a reference synthetic metaschoepite. Such a high binding energy component is interpreted as a component having a U(VI) oxide hydrate character, either as polynuclear surface oligomers and/or as amorphous schoepite-like (surface) precipitates. Its pH dependence suggests that a binding of polynuclear species at quartz surfaces and/or a formation of amorphous schoepite-like (surface) precipitates is favored when the proportion of aqueous polynuclear species increases. A second surface component exhibits binding energies for the U4f core levels at values significantly lower ($\Delta$E_b=1.2 eV) than for metaschoepite, evidencing uranyl ions in a distinct coordination environment. Such a low binding energy component may be attributed to monomeric uranyl surface complexes on the basis of published EXAFS data. Such a hypothesis is supported by a major contribution of the low binding energy component to the U4f XPS spectra of reference samples for uranyl sorbed on quartz from very acidic 10^{−3} M uranyl solutions where UO_2^{2+} ions predominate.
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http://hal.in2p3.fr/in2p3-00186813
Contributor : Béatrice Forrler Connect in order to contact the contributor
Submitted on : Monday, November 12, 2007 - 3:22:18 PM
Last modification on : Wednesday, September 22, 2021 - 3:40:04 PM

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A. Froideval, M. del Nero, R. Barillon, J. Hommet, G. Mignot. pH dependence of uranyl retention in a quartz/solution system: an XPS study. Journal of Colloid and Interface Science, Elsevier, 2003, 266, pp.221-235. ⟨10.1016/S0021-9797(03)00528-9⟩. ⟨in2p3-00186813⟩

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