First experimental determination of the solubility constant of coffinite
Résumé
Dissolution experiments have been performed in order to determine the solubility constant of coffinite, USiO 4. Several assemblages of phases were used in under-saturated experiments performed in 0.1 mol L-1 HCl under Ar atmosphere, as well as in air. These samples were fully-characterized and were composed of either USiO 4 , solely, or USiO 4 and additional oxide byproducts that resulted from the synthesis procedure. The solubility constant of coffinite was determined at 25°C and 1 bar (log *K S °(USiO 4 , cr) =-5.25 ± 0.05), as well as the standard free energy of formation of coffinite (Δ f G°(298 K) =-1867.6 ± 3.2 kJ mol-1), which enables one to infer the relative stability of coffinite and uraninite as a function of groundwater composition. Geochemical simulations using PHREEQC 2 software and the Thermochimie data base indicate that coffinite precipitates at 25°C under reducing conditions, at pH = 6, for H 4 SiO 4 (aq) concentration of 7 10-5 mol L-1 and U(OH) 4 (aq) concentration of 10-11 mol L-1. The Δ f G°
Domaines
Matériaux| Origine | Fichiers produits par l'(les) auteur(s) |
|---|
Loading...