title: Effect of temperature on the complexation of uranium(VI) with fluoride in aqueous solutions.
abstract: Complexation of U(VI) with fluoride at elevated temperatures in aqueous solutions was studied by spectrophotometry. Four successive complexes, UO(2)F(+), UO(2)F(2)(aq), UO(2)F(3)(-), and UO(2)F(4)(2-), were identified, and the stability constants at 25, 40, 55, and 70 degrees C were calculated. The stability of the complexes increased as the temperature was elevated. The enthalpies of complexation at 25 degrees C were determined by microcalorimetry. Thermodynamic parameters indicate that the complexation of U(VI) with fluoride in aqueous solutions at 25 to 70 degrees C is slightly endothermic and entropy-driven. The Specific Ion Interaction (SIT) approach was used to obtain the thermodynamic parameters of complexation at infinite dilution. Structural information on the U(VI)/fluoride complexes was obtained by extended X-ray absorption fine structure spectroscopy.
authors.affiliation: Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Guoxin
authors.initials: G
authors.lastname: Tian
authors.forename: Linfeng
authors.initials: L
authors.lastname: Rao