X-ray spectroscopic investigations of fluids in the hydrothermal diamond anvil cell: The hydration structure of aqueous La3+ up to 300 °C and 1600 bars
The first direct measurements are reported for the structure of the hydrated La3+ ion in an aqueous solution (containing 0.007 m La) over a range of temperatures from 25 to 300 °C and pressures up to 1600 bars. The radial distribution of atoms around the La3+ ion was measured using the X-ray absorption fine structure (XAFS) technique. La L3-edge spectra were collected in the fluorescence mode from nitrate solutions in a modified hydrothermal diamond anvil cell using the PNC-CAT X-ray microprobe at the Advanced Photon Source, Argonne National Laboratory. Analysis of the XAFS spectra collected at all temperatures indicates that each La3+ ion has a hydration number of nine and that the solvating waters surround the ion in a tricapped trigonal prismatic arrangement. As temperature is increased from 25 to 300 °C, the bond distance between the equatorial-plane O atoms and the La3+ ion increases from 2.59 ± 0.02 to 2.79 ± 0.04 Å, whereas the bond distance between La3+ and the O atoms at the ends of the prism decrease to 2.48 ± 0.03 Å. This study also demonstrates the unique capability of the modified hydrothermal diamond anvil cell for in situ low energy X-ray spectroscopic analysis of elements in dilute aqueous solutions at elevated temperatures and pressures.
Physics, Astronomy, and Materials Science
Anderson, Alan J., Sumedha Jayanetti, Robert A. Mayanovic, William A. Bassett, and I-Ming Chou. "X-ray spectroscopic investigations of fluids in the hydrothermal diamond anvil cell: The hydration structure of aqueous La3+ up to 300° C and 1600 bars." American Mineralogist 87, no. 2-3 (2002): 262-278.