Characterization of Heavy Metal Incorporation in Calcite by XAFS Spectroscopy

Zn and Co K-edge XAFS have been analyzed for spectra obtained from synthetic calcite that incorporated trace amounts of zn2+ and co2+ during growth from aqueous solutions at room temperature.Zn and Co concentrations in the calcite ranged from 250 to 2150 ppm.Analysis of the first shells indicates that the immediate coordination of both metal ions is approximately six oxygens at 2.11-2.12 A. These results are consistent with octahedral coordination at the unique Ca site in calcite.The observation that Co and Zn attain similar coordination in the bulk following incorporation suggests that their strongly contrasting surface site preferences are not expressed after being buried by subsequent growth layers.