Structural characterization of Am incorporated into calcite: a TRLFS and EXAFS study.

Calcite homogeneously doped with Am(III) and Cm(III) was synthesized in a mixed-flow reactor. The mechanism of incorporation of these actinides (An) into calcite was investigated by time-resolved laser fluorescence spectroscopy. Two different An(III)/calcite species were found. One has been identified as ions bonded onto the calcite surface. The second An(III) species has lost its complete hydration sphere and is incorporated into the calcite bulk structure. Both Cm(III)/calcite and Am(III)/calcite complexes have been characterized by their fluorescence emission spectra and lifetimes. Structural parameters of the incorporated Am(III) species determined by EXAFS indicate a coordination number of 6.3+/-0.6 and distances of 2.40+/-0.01 A for the first AmO shell.