Quantitative charge state analysis of manganese biominerals in aqueous suspension using scanning transmission X-ray microscopy (STXM) |
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Authors: | K Pecher D McCubbery E Kneedler J Bargar L Cox B Tonner |
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Institution: | 1 Dept. of Physics, University of Central Florida, Orlando, FL USA 2 OGI School of Engineering, Oregon Health & Sciences University, Beaverton, OR 97006 USA 3 Surface/Interface Inc., Sunnyvale, CA USA 4 Institut für Nukleare Entsorgung, Forschungszentrum Karlsuhe, Germany 5 Stanford Synchrotron Radiation Laboratory, SLAC, Stanford, CA USA 6 Advanced Light Source, LBNL, Berkeley, CA USA 7 University of Southern California, Earth Sciences, Los Angeles CA 90089 USA |
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Abstract: | We have applied Scanning Transmission Soft X-ray Microscopy (STXM) to investigate the charge state distribution of Mn in two kinds of Mn-biominerals, Mn nodules collected from Lake Michigan sediments and Mn precipitates formed by spores of a marine bacillus SG-1 under transport limited reaction conditions. A data analysis technique was developed, which allows for extraction of spatially resolved 2-d charge state maps of manganese on a submicron level. We find that the charge state of Mn dominates the spectral shape of L-edge spectra of environmentally important single oxidation state Mn minerals and that spectra of mixed oxidation state oxides can be modelled by a combination of appropriate single oxidation state reference spectra. Two-dimensional maps of charge state distributions clearly reveal domains of different oxidation states within single particles of Mn-micronodules. Spots of preferred accumulation of Mn(II) were found, which indicates biogenic precipitation of Mn(II)-species as a first step of nodule formation. The presence of Mn(III) in the studied sediment samples suggests the involvement of one-electron oxidation processes and reaction conditions which inhibit or slow down the disproportionation of Mn(III)-products. Under transport limited conditions, Mn oxidation products formed by spores of the marine bacillus SG-1 can vary from cell to cell. The presence of significant amounts of Mn(III) containing species points to the involvement of one-electron oxidation reactions as in the case of the micro-nodules. Our technique and the results obtained form a new basis for the mechanistic understanding of the formation of Mn biominerals in the environment. |
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