JRP CALL information
Supported By

European Commission

Short description of the work
The speciation of uranium (VI) in aqueous media in presence of sulfates is complex with the coexistence of various species according to the sulfate concentration and the pH of the medium. In acidic conditions, UO2(SO4)(aq), UO2(SO4)22- and UO2(SO4)34- may co-exist. At pH > 3, the speciation is even more complex as oligomeric species or ternary species may form as a consequence of the uranium hydrolysis. Therefore, it is a challenge to perform an accurate characterization of the speciation in view to determine not only the stoichiometry of the species in solution, but also their structure. Sulfate ions have the ability to bind uranium (VI) in two ways, as monodentate or as bidentate fashion, and some contradictory results were obtained, especially at low sulfate ratio. According to authors, a monodentate or a bidentate coordination is evidenced for the 1:1 complex. In this context, we would like to use the specific properties of ionic liquids (IL) to investigate the coordination of sulfate ions with uranium (VI). In this kind of solvent constituted only by ions and easy to dry, we can get rid of the uranium (VI) hydrolysis. Also, we can choose the dissolved uranyl and sulfate salts so that their counter-ions are identical to the ions constituting the IL. In that way, we avoid any interferences due to counter-ions, the studied system being composed only by uranyl, sulfate and the cation and anion of the IL.
We used this experiment at the uranium L3 edge to identify the stoechiometry and configuration of sulfato-complexes of uranium(VI) in ionic liquids, as a function of the sulfate/uranium ratio in solution. We show in particular the formation of a solid compound which corresponds to the 1:1 complex where the sulfate group is bound to uranium in a bidentate fashion.

Main visitor contact data
Name: Dr Clotilde GAILLARD
Organisation: IPNL

JRP Identification
JRP nr: TALI-C05-15
JRP title: Investigation of sulfato-complexes of uranium(VI) in a hydrophobic ionie liquid
JRP scope: Scope 1: Actinide separation chemistry

Visited Associated Pooled Facility
Visited APF during the stay: HZDR - ROBL
Name of the APF Contact Person: Scheinost

Other APF and organisation involved in the JRP
Other organisations involved: Institut Pluridisciplinaire Hubert Curien (Maria Boltoeva);
Other APF involved in the project:

Description of the work done at the associated pooled facility
Start date of the stay: 10/7/2015
End date of the stay: 10/10/2015
Quantity of access: 9
Access Unit: Shifts

Other APF visitors of the JRP during the stay
Visitor 2: Dr Christoph Hennig
Visitor 3: Dr Kristina KVASHNINA