A modelling exercise on the importance of ternary alkaline earth carbonate species of uranium(VI) in the inorganic speciation of natural waters

Thomas Vercouter (1) , Pascal E. Reiller (1) , Eric Ansoborlo (2) , Laureline Février (3) , Rodolphe Gilbin (3) , Claire Lomenech (4) , Violaine Philippini (5)

1 LANIE - Laboratoire de développement Analytique Nucléaire Isotopique et Elémentaire
2 CETAMA - Commission des méthodes d'analyse du CEA
3 IRSN - Institut de Radioprotection et de Sûreté Nucléaire
4 ECOMERS - Ecosystèmes Côtiers Marins et Réponses aux Stress
5 ICN - Institut de Chimie de Nice

Predictive modelling of uranium speciation in natural waters can be achieved using equilibrium thermodynamic data and adequate speciation software. The reliability of such calculations is highly dependent on the equilibrium reactions that are considered as entry data, and the values chosen for the equilibrium constants. The working group " Speciation " of the CETAMA (Analytical methods establishment committee of the French Atomic Energy commission, CEA) has organized a modelling exercise, including four participants, in order to compare modellers' selections of data and test thermodynamic data bases regarding the calculation of U(VI) inorganic speciation. Six different compositions of model waters were chosen so that to check the importance of ternary alkaline earth carbonate species of U(VI) on the aqueous speciation, and the possible uranium solid phases as solubility-limiting phases. The comparison of the results from the participants suggests i) that it would be highly valuable for end-users to review thermodynamic constants of ternary carbonate species of U(VI) in a consistent way and implement them in available speciation data bases, and ii) stresses the necessary care when using data bases to avoid biases and possible erroneous calculations.

Mots clés: Uranium; speciation; carbonate complexes; calcium; magnesium; solubility; thermodynamic calculation; natural water

Domaines: Chimie

Thomas Vercouter, Pascal E. Reiller, Eric Ansoborlo, Laureline Février, Rodolphe Gilbin, et al.. A modelling exercise on the importance of ternary alkaline earth carbonate species of uranium(VI) in the inorganic speciation of natural waters. Applied Geochemistry, 2015, Geochemical Speciation Codes and Databases, 55, pp.192-198. ⟨10.1016/j.apgeochem.2014.11.016⟩. ⟨hal-01313947⟩