Micro-spectroscopic investigation of selenium-bearing minerals from the Western US Phosphate Resource Area |
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| Authors: | Amy?L?Ryser Email author" target="_blank">Daniel?G?StrawnEmail author Matthew?A?Marcus Jodi?L?Johnson-Maynard Mickey?E?Gunter Gregory?M?ller |
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| Institution: | (1) University of Idaho, Moscow, Idaho, 83844-2339;(2) Lawrence Berkeley National Laboratory, Berkeley, California, 94720; |
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| Abstract: | Mining activities in the US Western Phosphate Resource Area (WPRA) 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 (XAS), 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 (XANES) for the bulk rock samples revealed multiple oxidation states, with peaks indicative of Se(-II),
Se(IV), and Se(+VI) 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-EXAFS) 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. |
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