Interaction of uranium(VI) with various modified and unmodified natural and synthetic humic substances studied by EXAFS and FTIR spectroscopy

Speciation of naturally-accumulated uranium in an organic-rich soil of an alpine region (Switzerland)

“…In contrast, natural organic matter is a mixture of many organic compounds with numerous and uncharacterized functional groups. Schmeide et al (2003) investigated complexes between humic acid and U(VI) by XAS but the fits focused only on the first two coordination shells presumably due to difficulties in fitting higher shells. Because humic acid contains numerous functional groups such as carboxylic and phenolic groups, destructive interference among the shells could account for the minimal intermediate-range structure observed.…”

“…A possible explanation for the presence of a P shell in these organic-rich samples is the formation of ternary complexes by which the positively Table 6 Comparison of U-O distances (axial and equatorial) and U-C obtained in from several literature studies. Schmeide et al (2003) charged uranyl bridges the negatively charged phosphate and the predominantly negatively charged groups of the organic material. The existence of such complexes was previously suggested by Paludan and Jensen (1995) and Schnitzer and Khan (1972).…”

“…This correlation results from the fact that the humic and fulvic acids, which are the main components of aqueous organic matter (OM), are efficient at exchanging protons with metals thereby forming aqueous complexes (Stumm and Morgan, 1996). However, the detailed study of uranium-humic or -fulvic acid complexes has not yielded structures due to the complexity of the organic compound despite the use of powerful techniques such as X-ray absorption spectroscopy (Schmeide et al, 2003). In addition, microbially-catalyzed reduction of metals in organic matter-rich environments was observed in which microorganisms use metals as terminal electron acceptors and the humic substances as donor or as an electron shuttle for anaerobic respiration (Lovley et al, 1996;Gu and Chen, 2003;Gu et al, 2005;Grybos et al, 2007;Wall and Krumholz, 2006).…”

Study on the Oxidative Leaching of Uranium from the Lignite in the CO32-/HNing1, Li2, Zhang3 et al. 2017Geofluids2000View full textAdd to dashboardCite

“…It has been studied previously that humic acid provides a lot of functional groups which are able to combine with the metal ions, including the carboxyl [22], phenolic hydroxyl, and alcoholic hydroxyl [23]. In the study, the phenolic hydroxyl and alcoholic hydroxyl groups may be the major functional groups combined with uranium.…”

Uranyl complexation by monodentate nitrogen donor ligands. A relativistic density functional study

“…Among the large variety of functional groups of humic substances, carboxyl groups are considered as most important for metal ion complexation [6]. Yet, other reactive groups may also contribute to the complexation of uranium, for example, phenolic and aliphatic OH, amino groups, other N-or even S-containing groups [7][8][9][10][11][12]. There is some evidence, both experimental [7] and theoretical [9], for the contribution of the phenolic OH groups.…”