JRP 02-19

Partners

CNRS

CEA

EC-JRC-ITU

FZD

Contact

Dr C. le Naour
CNRS-IN2P3-UPS - Institut de Physique Nucléaire - Radiochimie, Bât. 100 - 91406 Orsay cedex France
Phone + 33 (0) 1 69 15 51 74
E-mail e-mail

Spectroscopic approach of aqueous chemistry of Protactinium(V)

Status

 
Terminated - Planned from March 2005 till September 2006

Goals

This joint research project is part of a broader programme, devoted to the study of the chemical properties of protactinium in aqueous solution. The aim of one part of this programme (outer the frame of Actinet) is the determination of standard thermodynamic data, relative to equilibria that could occur in the environment (complexation constants, Gibbs energy, enthalpy, entropy heat capacity changes). The main objective of the other part (in the frame of Actinet) is to collect information about:

  • the structure of Pa(V) species in solution in different inorganic acids (perchloric, hydrochloric, hydrofluoric, sulfuric, trifluoromethanesulfonic…) with macro-amount of element;
  • the structure of solid compound of Pa(V).

Although this joint research project is mainly devoted to a fundamental aspect of protactinium chemistry in aqueous solution, it also contributes to the development of thorium fuel reactors and the investigation of the presence of 231Pa in nuclear waste. Furthermore, the structural and thermodynamic data on protactinium are also useful for the modelling of the behaviour of protactinium in the environment.

Expected results

Several 231Pa samples from IPN-Orsay stock were purified from their daughters (227Ac, 227Th, 223Ra) using the anion-exchange technique. Protactinium was sorbed on the resin from concentrated HCl and eluted with a mixture HF/HCl. Each sample corresponding to a mineral acid at a given concentration was obtained after several cycles of evaporation / dissolution. Various samples in HF, H2SO4 and HCl were prepared in this way, with Pa concentration ranging between ~10-4 and ~10-2M, and transferred to CEA-Valrhô for spectroscopic studies.

Spectrophotometric measurements were performed in concentrated HCl media. Difficulties encountered in getting reproducible absorption spectra of Pa(V) have led the researchers of CEA to develop a suitable protocol involving the reduction of Pa(V) to Pa(IV). Spectra of Pa(V) were registered during the reoxidation of Pa(IV) and their variations with time also studied. However, the strong absorption of hydrochloric acid in the UV region, seems to interfere with the absorption of Pa(V) itself, complicating the interpretation of the spectra, especially at the wavelengths lower than 220 nm.

The first XAS measurements on protactinium(V) were carried out at ROBL/ESRF. XANES and EXAFS spectra of Pa(V) in H2SO4 13 M and HF 0.5M have shown unambiguously the absence of a transdioxo unit in protactinium(V) species, unlike other actinides as U and Np. The presence of one single Pa-O oxo bond in concentrated sulphuric acid has been established whereas no oxo bond has been found in hydrofluoric acid.

Publications

  • Le Naour C., Trubert D., Di Giandomenico M.V., Fillaux C., Den Auwer C., Moisy P. and Hennig C..- First Structural Characterization of a Protactinium(V) Single Oxo Bond in Aqueous Media- In: Inorg. Chem., 44(2005), p. 9542-9546

Reports