title: Environmental modeling of uranium interstitial compositions of non-stoichiometric oxides: experimental and theoretical analysis.
abstract: Study of uranium interstitial compositions of non-stoichiometric oxides UO2+x (x ∈ 0.1-0.02) in gas and condense phases has been presented, using various soft-ionization mass spectrometric methods such as ESI-, APCI-, and MALDI-MS at a wide dynamic temperature gradient (∈ 25-300 °C). Linearly polarized vibrational spectroscopy has been utilized in order to assign unambiguously, the vibrational frequencies of uranium non-stoichiometric oxides. Experimental design has involved xUO2.66·yUO2.33, xUO2.66·yUO2.33/SiO2, xUO2.66·yUO2.33/SiO2 (NaOH) and SiO2/x'NaOH·y'UO2(NO3)2·6H2O, multicomponent systems (x = 1, y ∈ 0.1-1.0 and x' = 1, y' ∈ 0.1-0.6) as well as phase transitions UO2(NO3)2·6H2O → {U4O9(UO2.25)} → U3O7(UO2.33) → U3O8(UO2.66) → {UO3}, thus ensuring a maximal representativeness to real environmental conditions, where diverse chemical, geochemical and biochemical reactions, including complexation and sorption onto minerals have occurred. Experimental factors such as UV-irradiation, pH, temperature, concentration levels, solvent types and ion strength have been taken into consideration, too. As far as uranium speciation represents a challenging analytical task in terms of chemical identification diverse coordination species, mechanistic aspects relating incorporation of oxygen into UO 2+x form the shown full methods validation significantly impacts the field of environmental radioanalytical chemistry. UO2 is the most commonly used fuel in nuclear reactors around the globe; however, a large non-stoichiometric range ∈ UO1.65-UO2.25 has occurred due to radiolysis of water on UO2 surface yielding to H2O2, OH(·), and more. Each of those compositions has different oxygen diffusion. And in this respect enormous effort has been concentrated to study the potential impact of hazardous radionuclide on the environment, encompassing from the reprocessing to the disposal stages of the fuel waste, including the waste itself, the processes in the waste containers, the clay around the containers, and geological processes. In a broader sense, thereby, this study contributes to field of environmental analysis highlighting the great ability of various soft-ionization MS methods, particularly, MALDI-MS one, for direct assay of complex multicomponent heterogeneous mixtures at fmol-attomol concentration ranges, along with it the great instrumental features allowing, not only meaningful quantitative, but also structural information of the analytes, thus making the method indispensable for environmental speciation of radionuclides, generally.
authors.affiliation: Lehrstuhl für Analytische Chemie, Institut für Umweltforschung, Fakultät für Chemie, Universität Dortmund, Otto-Hahn-Straße 6, 44227, Dortmund, Nordrhein-Westfalen, Germany. B.Ivanova@web.de.
authors.forename: Bojidarka
authors.initials: B
authors.lastname: Ivanova
authors.affiliation: Lehrstuhl für Analytische Chemie, Institut für Umweltforschung, Fakultät für Chemie, Universität Dortmund, Otto-Hahn-Straße 6, 44227, Dortmund, Nordrhein-Westfalen, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Spiteller
mesh_terms: D055593:Geological Phenomena; D013058:Mass Spectrometry; D008962:Models, Theoretical; D010087:Oxides / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry; D013696:Temperature; D014501:Uranium / Q000737:chemistry*; D017974:Uranium Compounds / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D010087:Oxides; D017974:Uranium Compounds; D014867:Water; D014501:Uranium; D012822:Silicon Dioxide; C047385:uranium oxide
keywords: Mass spectrometry; Quantum chemistry; Uranium speciation analysis; Vibrational spectroscopy