Thermodynamics of the System: Americium(lll)-Fluoride—Stability Constants, Enthalpies, Entropies, and Solubility Product

Abstract

Stability constants for the 1 : 1 and 1 : 2 complexes between Am 3+ and F" were determined in 0.1 M NaC10 4 media by the cation exchange technique. Complexation enthalpies and entropies were calculated by the application of the van't Hoff relationship to the stability constants determined at 5, 25, and 45°C. The stability constants at 25°C are K, = 386 (± 10), K 2 = 147 (+ 12). The associated enthalpies and entropies are ΔΗ ι = 22.9 (± 1.6) kJ/m, AS, = 126 (± 5) J/m-°K, and ΔΗ 2 = 1.6(±5)kJ/m, AS 2 = 47 (± 17) J/m-°K. In addition, an approximate value for the solubility product of AmF, has been determined (K sp = 5.

Tributylphosphate Extraction Behavior of Bismuthate-Oxidized Americium

“…One attribute of oxidized americium species is that they are soluble in aqueous solution in the presence of excess fluoride ion. This is in contrast to the behavior of Am 3+ , which forms the insoluble AmF 3 complex and precipitates out of solution under similar conditions . Hence, the introduction of fluoride ions can be used as a test for the presence of oxidized americium species.…”

Thermodynamics of Cm(III) in Concentrated Electrolyte Solutions. Fluoride Complexation in 0-5 m NaCl at 25°C

“…Recently an overview about the spectroscopic evaluation of thermodynamics of trivalent actinides in brines is published [7,8]. Previous studies on the fluoride complexation of trivalent actinides have been performed mainly on Am(III) [9][10][11][12][13]. The available literature data for Am(IH) are compiled and critically evaluated in the recently published ΝΕΑ Thermodynamic Database [14].…”