Manganese K-edge XANES studies of Mn speciation in Lac des Allemands as a function of depth

摘要

X-Ray absorbance near edge spectroscopy (XANES) was used to identify variations in oxidation states of Mn with depth in a core sample. The core sample was collected from a small lake (Lac des Allemands) located in southeastern Louisiana. Samples of core segments were split into subsamples, one dried prior to analysis and a second kept wet. Upper core segments in the wet subsample was found to have K-edge energies 1.5 eV below the lower core segments, suggesting the presence of Mn(II) and/or Mn(III). The dominant oxidation state in all core segments was Mn(W), with the bottom core samples containing almost entirely Mn(M. This change in oxidation state probably resulted from the depletion of water at depth and the presence of anaerobic conditions. Manganese oxidations states were also found to change in pre-treated (dried) samples. Significant concentrations of Mn(II)/Mn(III) were found in the wet core segments near the water/sediment interface but these states disappear after drying. (C) 2003 Elsevier B.V. All rights reserved.