Spectroscopic Study of Cm(III) Sorption onto -Alumina

The surface sorption of Cm(III) onto aqueous suspensions of alumina is investigated by time-resolved laser fluorescence spectroscopy (TRLFS). The experiment is performed under an Ar atmosphere at an ionic strength of 0.1 M NaClO₄. The pH is varied between 2 and 10 and the metal ion concentration between 2.7×10⁻⁸ and 4.5×10⁻⁵ mol/L. With increasing pH, two Cm(III)–alumina surface species are identified which are attributed to≡Al–O–Cm²⁺(H₂O)₅ and≡Al–O–Cm+(OH)(H₂O)₄. The two curium–alumina surface complexes are characterized by their emission spectra (peak maxima at 601.2 nm and 603.3 nm, respectively) and fluorescence emission lifetime (both 110s). In the concentration range investigated, the surface complex formation is not dependent on the metal ion concentration but only on the pH. Additionally, the concentration ratio of the two surface species is found to be independent of the metal ion concentration. No spectroscopic evidence for the presence of "strong" and "weak" sites can be found at different surface coverages.