Coordination of U(IV) and U(VI) sulfate hydrate in aqueous solution

Sulfuric acid has been used to perform in situ leaching of uranium ore at several sites in the world, among them in Königstein/Germany. The remaining leaching solvents cause questions concerning their environmental problems. The actual thermodynamic data, describing the species distribution in aqueous solution, are not sufficient because typical leaching solutions easily exceed the limit of ionic strengths where conventional models provide trustful results. The application of spectroscopic techniques may help to provide the required data. Therefore, the coordination of U(IV) and U(VI) sulfate in aqueous solutions with high ionic strengths has been recently investigated by several spectroscopic techniques (mainly EXAFS) combined with XRD studies and DFT calculations. The observed results expand the actual knowledge of the aquatic chemistry which is based mainly on thermodynamic data. The recent results are summarized in this contribution.