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Curti, E.*; Aimoz, L.*; Kitamura, Akira
Journal of Radioanalytical and Nuclear Chemistry, 295(3), p.1655 - 1665, 2013/03
Times Cited Count:27 Percentile:88.86(Chemistry, Analytical)Se is a major dose-determining redox-sensitive nuclide in safety analysis of radioactive waste disposal sites. In aqueous solutions, selenium forms soluble anionic species (SeO and SeO) that hardly sorb on negatively charged surfaces of common host-rock minerals. However, Se is known to have a strong affinity with sulphides and interacts with pyrite, a common minor mineral of argillaceous rocks being considered as host rocks for radioactive waste repositories in Switzerland etc. In this study, we present micro- and bulk X-ray spectroscopy data (-XRF, -XANES, and EXAFS) showing that, under nearly anoxic conditions, dissolved SeO and SeO sorb directly onto the pyrite surface and are subsequently reduced to Se with increasing ageing time (up to 8 months). These results suggest that the mobility of Se released from radioactive waste could efficiently be reduced through uptake on the pyrite surface followed by transformation into a sparingly soluble reduced form.
Kitamura, Akira; Curti, E.*; Aimoz, L.*
no journal, ,
In the present study, the interaction of Se(IV,VI) species with pyrite under strictly anoxic conditions was investigated using micro X-ray spectroscopy (-XAS). Polished chips of natural pyrite (Navajun, Spain) were reacted with 10 M NaSe(IV)O or NaSe(VI)O solutions at 80C during two months. Micro X-ray Fluorescence (-XRF) maps and -XAS spectra were collected in suitable sample holders flushed with inert gas at the Swiss Light Source (X05 beamline), using a beam focused to roughly 11 m. A highly heterogeneous distribution of Se on the pyrite surface was observed on the -XRF maps. Several highly-concentrated Se spots of a few m size were detected, surrounded by areas with low and uniform Se-level distribution. Micro X-ray Absorption Near-Edge Spectra (-XANES) in both regions indicate that Se(IV) and Se(VI) were partially reduced to Se(0).
Kitamura, Akira; Curti, E.*; Aimoz, L.*
no journal, ,
A batch experiment was performed to investigate sorption of selenium(IV/VI) onto pyrite (FeS). Polished chips of natural pyrite were reacted with selenium(IV/VI) solutions with pH 89 for 2 months at 80 C under N atmosphere. Micro X-ray Fluorescence (-XRF) maps and Micro X-ray Absorption Spectra (-XAS) were collected in suitable sample holders flushed with inert gas. Crashed grains of natural pyrite were also used for comparison with pyrite chips. It was found that equivalent sulfur was dissolved to solutions after selenium sorption, sorption of selenium onto pyrite was highly heterogeneous, and both tetravalent and hexavalent selenium were reduced to selenium(0) after sorption onto pyrite.