Micro-spectroscopic investigation of selenium-bearing minerals from the Western US Phosphate Resource Area

Abstract

Mining activities in the US Western Phosphate Resource Area ͑WPRA͒ have released Se into the environment. Selenium has several different oxidation states and species, each having varying degrees of solubility, reactivity, and bioavailability. In this study we are investigating the speciation of Se in mine-waste rocks. Selenium speciation was determined using bulk and micro-x-ray absorption spectroscopy ͑XAS͒, as well as micro-x-ray fluorescence mapping. Rocks used for bulk-XAS were ground into fine powders. Shale used for micro-XAS was broken along depositional planes to expose unweathered surfaces. The near edge region of the XAS spectra ͑XANES͒ for the bulk rock samples revealed multiple oxidation states, with peaks indicative of Se͑ϪII͒, Se͑IV͒, and Se͑ϩVI͒ species. Micro-XANES analysis of the shale indicated that three unique Se-bearing species were present. Using the XANES data together with ab initio fitting of the extended x-ray absorption fine structure region of the micro-XAS data ͑micro-EXAFS͒ the three Se-bearing species were identified as dzharkenite, a di-selenide carbon compound, and Se-substituted pyrite. Results from this research will allow for a better understanding of the biogeochemical cycling of Se in the WPRA.

Selenium adsorption to aluminum-based water treatment residuals

“…These values were similar to those obtained from and support the formation of either monoclinic [49] or red [43] elemental Se (Table 2).…”

Selenium Speciation in Biofilms from Granular Sludge Bed Reactors Used for Wastewater Treatment

“…Figure 2 shows the normalized Se K-edge XANES spectra collected for a selection of model compounds with characteristic selenium valences. The Se K-edge position is sensitive to the valence of Se [3,[7][8][9][10]. In contrast to previous studies, no simple relation is found between the Se K-edge position and the selenium valence.…”

“…However the edge position for Se(-I) (as in FeSe 2 and CuSe 2 ) is identical to that for elemental Se (~ 12659.7 eV in our study). We did not select the edge crest maxima to derive valences (see [10]) because this region is also affected by the local structures around Se. It is therefore unreliable for this purpose.…”

Oxidation state and local environment of selenium in alkali borosilicate glasses for radioactive waste immobilisation

“…Energy calibration was performed by measuring a sample of metallic Se 0 and setting the K-edge, as determined by the maximum of the first derivative, to 12,658.0 eV. This value is consistent with those obtained in other studies [24][25][26]. All measured edge energies given in this publication were determined by this method.…”