742-10 X-ray Microspectroscopy Analysis of Phosphorus Speciation in an Acidic Organic Soil.

See more from this Division: S02 Soil Chemistry
See more from this Session: Oxyanions in Soil Environments: II

Wednesday, 8 October 2008: 4:00 PM
George R. Brown Convention Center, 360C

Dean Hesterberg1, Ian McNulty2 and Kimberly Hutchison1, (1)Soil Science, North Carolina State University, Raleigh, NC
(2)Advanced Photon Source, Argonne National Laboratory, Argonne, IL
Abstract:
Because organic soils are often located near surface water bodies, they have a vital role in protecting water quality. To determine how phosphate mobility is affected by reduction and oxidation processes in poorly-drained organic soils, our goal is to quantify proportions of phosphate bound with redox-active soil Fe(III) vs redox-inactive Al(III). We studied an acid soil (pH 4.8) containing total P, Fe, and Al concentrations of 23, 43, and 380 mmol/kg. Micro-XANES analyses at both the phosphorus and aluminum K-edges were performed on the sample to try to identify Fe(III)-bonded PO4 based on a pre-white-line peak, and PO4 bonded with Al by comparison with mineral standards.  Micro-XANES helps overcome limitations of bulk XANES analysis for soil samples with low P concentrations.  Based on micro-x-ray fluorescence analysis using an ~50 x 50 nm synchrotron x-ray beam; P, Al, and Si were heterogeneously distributed within the sample as expected. Phosphorus K-edge micro-XANES spectra collected at various locations on the sample showed little or no evidence for Fe(III)-bonded PO4. Aluminum K-edge micro-XANES spectra were usually characteristic of Al-hydroxide mineral, likely because of the 16-fold greater concentration of Al vs P.  Detailed and quantitative speciation of soil P remains a challenge, but will be important for determining mechanisms and predicting the extent of reductive P dissolution in a given soil.

See more from this Division: S02 Soil Chemistry
See more from this Session: Oxyanions in Soil Environments: II