Technetium sorption properties of Fe2+-bearing minerals and different metal sulfides were studied by batch and column experiments. Pure stibnite (SbS3), pyrrhotite (FeS), pyrite (FeS2), galena (PbS) and loell ingite (FeAs2) fix Tc to a great extent (> 95 % of TcO4- starting inventory). They appear to be favourable backfill materials for redox-sensitive radionucli-des. Physico-chemical processes of fixation and possible fixation modes are discussed.

This paper describes the development and testing of a chemical procedure for determining the tetravalent and hexava-lent states of uranium in aqueous media at concentration as low as 10−10M. Results show the U(IV) stability towards fast modifications of the pH of the solution with oxygen free hydrochloric acid. Some results on the oxidation kinetic of the uranium tetravalent state versus the HCl and uranium concentrations as well as the Fe(III) content are presented.

The speciation of the Am(III) ion in various chemical states is illustrated using laser-induced photoacoustic spectroscopy (LPAS). Based on these reference LPAS spectra, the actual chemical states of Am(III) in one of Gorleben groundwaters are systematically verified. The a-radiolytic oxidation of Am(III) to Am(V) in the concentrated NaCl solution and their carbonate complexation are also speciated for the purpose of demonstration.