PMID: 16646462May 2, 2006Paper

Evidence of a stable uranyl site in ancient organic-rich calcite

Environmental Science & Technology
Shelly D KellyKenneth M Kemner

Abstract

The mechanism of uranium (U) incorporation into calcite (calcium carbonate) is of fundamental importance to the fate and transport of U at the surface and in the shallow subsurface and has implications for (a) the accuracy of U-Pb and U-series isotope ratio methods used to determine the ages of ancient deposits and (b) potential remediation strategies based on sequestration of U in the subsurface. Extended X-ray absorption fine structure (EXAFS) spectroscopy is uniquely suited to the study of U-calcite systems. The sensitivity of the EXAFS spectrum to the local atomic Ca coordination about U(VI) in the calcite structure results in an increase in the number and amplitude of Ca signals as the U(VI) becomes more ordered within the crystal structure. Our X-ray microprobe (10-microm) measurements of an ancient 298 million-year-old organic-rich calcite (calcrete) clearly revealed three coordination shells of Ca atoms, defining a well-ordered calcite structure about uranyl to a distance of approximately 6.5 angstroms. These results indicate that uranyl is incorporated at the Ca2+ site in calcite and that the uranyl environment may evolve over long time scales, becoming more calcite-like and more stable for long-term sequestration of u...Continue Reading

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Citations

Mar 15, 2011·Environmental Science & Technology·P Evan DreselMichael J Truex
Sep 22, 2011·Environmental Science & Technology·Shuao WangThomas E Albrecht-Schmitt
Oct 1, 2009·Ground Water·Bryant C JurgensMatthew K Landon
Sep 10, 2020·Frontiers in Chemistry·Anna Yu RomanchukStepan N Kalmykov
Feb 12, 2010·Environmental Science & Technology·Edward J O'LoughlinKenneth M Kemner
Jul 26, 2021·The Science of the Total Environment·Leja RovanSonja Lojen
Feb 21, 2008·Environmental Science & Technology·Frank HeberlingDirk Bosbach

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