Micro-XANES

KEYWORDS sulfide alteration, Acid Mine Drainage, micro-XRD, micro-XRF, micro-XANES. 

Micro-XRD and micro-XANES analyses showed that the earliest stage of sulfide alteration is marked by the progressive oxidation of sulfide-S to sulfate-S that is then rapidly leached out from the system. Sulfide oxidation starts from particle rims or from intra-grain microfractures and is accompanied by a progressive loss of sulfur sulfides are then pseudomorphically replaced by goethite and minor bemalite. In addition to sulfides, many gangue silicates are efficiently altered and only quartz is preserved within the altered layers. 

XANES analyses indicated the presence of both As3+ and As5+ species in the stack sample and that about one-third of the total As is trivalent (Paktunc 2008). X-ray mapping supplemented by micro-XANES analyses indicated that As is localized along thin rims around spherical Cu particles. These rims have higher As3+ species ranging from 34 to 40% of the total As. 

Walker, S.R., Jamieson, H.E., Lanzirotti, A., Andrade, C.F., Hall, G.E.M. 2005. The speciation of arsenic in iron oxides in mine wastes from the Giant gold mine, N.W.T. Application of synchrotron micro-XRD and micro-XANES at the grain scale. Canadian Mineralogist, 43, 1205-1224. 

We now consider the abstract presented in excerpt 8G, which reverses the emphases observed in excerpts 8C-8F. In excerpt 8G, moves 1 and 2 comprise the bulk of the abstract, and move 3 is just a single sentence. Much of the abstract is used to elucidate important gaps in the field that (1) a size-based standard for regulating atmospheric particulate matter is inadequate because it does not take into account chemical composition, and (2) compositional analyses are difficult, especially for metals, because they often exist in multiple oxidation states. These gaps help to establish the relevance of the authors work. Only in the last sentence do the authors mention their work specifically (move 3). Here, they identify their method (micro-XANES) and tell readers what results will be presented at the conference. 

Schulze, D. G., McCay-Buis, T., Sutton, S. R., and Huber, D. H. (1995). Manganese oxidation states in Gaeumannomyces-infested wheat rhizospheres probed by micro-XANES spectroscopy. Phytopathology 85, 990-994. 

Tokunaga, T.K., Sutton, S.R., Bajt, S., Nuessle, P. and Shea-McCarthy, G. (1998) Selenium diffusion and reduction at the water-sediment boundary micro-XANES spectroscopy of reactive transport. Environ. Sci. Technol., 32, 1092. 

Micro SXRF (Synchrotron-based micro-X-ray fluorescence) spectroscopy is an excellent tool to study elemental distributions on microscopic level. This method helps to understand the role of particular minerals in sorption properties of complex mineral assemblies. Iron and managanese oxide phases were detected in polished thin sections of natural zeolitic tuff by SXRF. This section was contacted with synthetic ground water containing Pu(V), and Pu was found to be predominantly associated with manganese oxide, but not with hematite [41]. Micro SXRF can be combined with micro-XANES, and micro-EXAFS to determine the oxidation state and coordination environment of Pu adsorbed at different regions of the tuff [42]. 

In order to obtain true understanding of redox processes in naturally-occurring micas, microanalyical techniques must be employed. If the material can be prepared as beveled grains or thinned thin sections and the region of interest is the top 10-100 A, then XPS or EELS can be used. For in situ analysis of Fe VEFe at 10x15 pm resolution in standard thin sections, synchrotron micro-XANES shows the best potential. 

Dyar MD, Delaney JS, Sutton SR, Guidotti CV (1997) In situ microanalysis and partitioning of ferric/ferrous in metapelite from western Maine. Geol Soc Am Aim Mtg, Salt Lake City, Utah, p A399 Dyar MD, Delaney JS, Sutton SR (2001) XANES spectra of Fe-rich micas. Eur J Mineral 13 1079-1098 Dyar MD, Lowe EW, Guidotti CV, Delaney JS (2002) Fe and Fe among sihcates in metapelites A synchrotron micro-XANES study. Am Mineral (in press)... 

Delaney JS, Sutton SR, NewviUe M, Jones JH, Hanson B, Dym MD, Schreiber H (2000) Synchrotron micro-XANES measrrrements of vanadium oxidation state in glasses as a function of oxygen fugacity ... 

Stohr J, Noguera C, Kendelewicz T (1984) Auger and photoelectron contributions to the electron-yield surface extended X-ray-absorption fine-structure signal. Phys Rev 630 5571-5579 Sutton SR, Bajt S, Delaney J, Schulze D, Tokunaga T (1995) Synchrotron X-ray fluorescence microprobe Quantification and mapping of mixed valence state samples using micro-XANES. Rev Sci Instrum 66 1464-1467... 

Figure 22. Micro-XANES data of a ferromanganese crust (Hlawatsch et al. 2001) recorded in transmission mode in spots of the same composition but differing thickness. The pre-edge is enhanced and the EXAFS amplitude is reduced by hole effect.

Messenger S, Walker RM (1998) Possible association of isotopically anomalous cluster IDPs with comet Schwassmann-Wachmann 3. Lunar and Planetary Science XXIX, 1906 Mosbah M, Curaud JP, Metrich N, Wu Z, Delaney JS, San Miguel A (1999) Micro-XANES with synchrotron radiation a complementary tool of micro-PIXE and micro-SXRF for the determination of oxidation state of elements. Application to geological materials. Nucl Instrum Methods Phys Res 158 214-220... 

Micro-XANES were obtained for Cu and Mn on the same beamline with the same experimental set-up as for the XRF The Fe spectra were collected as a single scan in fluorescence yield mode at selected points within the cross-section... 

Scordari, E, Dyar, M.D., Schingaro, E., Lacalamita, M., Ottolini, L. (2010) XRD, micro-XANES, EMPA and SIMS investigation on phlogopite single crystals from Mt. Vulture (Italy). Am. Mineral, 95,1657-1670. 

Terzano, R., Z. A. Chami, B. Vekemans, K. Janssens, T. Miano, and P. Ruggiero. 2008. Zinc distribution and speciation within rocket plants (Eruca vesicaria L. Cavaheri) grown on a polluted soU amended with compost as determined by XRF microtomography and Micro-XANES. Journal of Agricultural and Food Chemistry 56, no. 9 3222-3231. doi 10.1021/jf073304e. 

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