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

Abstract

International audiencePredictive 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 calculation

Efficiency of dihydroxamic and trihydroxamic siderochelates to extract uranium and plutonium from contaminated soils

“…These mlh estimates were then implemented in the database already used by Lofts et al (2015) and Vercouter et al (2015). Briefly, this database is an update of the one released in 2004 in the framework of the Common Thermodynamic Database Project (Van der Lee and Lomenech, 2004).…”

Rates and mechanisms of uranyl oxyhydroxide mineral dissolution

“…, and MgUO 2 (CO 3 ) 3 2À were included in the thermodynamic database for the equilibrium speciation calculations (Vercouter et al, 2015). Formation data for these ternary species have been determined in the last decade Brooks, 2006, 2008;Geipel et al, 2008;Lee and Yun, 2013), but few compiled thermodynamic databases have included them (e.g., they have been recently added to Thermochimie, www.thermochimie-tdb.com).…”

Impact of the uranium (VI) speciation in mineralised urines on its extraction by calix[6]arene bearing hydroxamic groups used in chromatography columns

“…However, to our knowledge, the speciation of U(VI) in mineralised urines has not been explored yet, despite its impact on U(VI) reactivity on the steps following the mineralisation such as chromatography columns extraction. The HYDRA database associated with the ME-DUSA software was updated with the most recent data [19] found in literature. Other missing species such as alkali and alkali-earth phosphate species, uranyl sulphate and hydroxide species were added with appropriate stability constants to complete the database.…”

“…This database is based on OECD-NEA 2003 update [17] of the 1992 report [18]. Constants missing from the HYDRA database were derived from recent literature [19] (see Appendix A for all the constant used). Activity coefficients were calculated by using Davies equations [20].…”