Influence of humic acid on the sorption of Eu (III)/Am (III)/Cm(III) onto γ-Al2O3 - a time-resolved laser fluorescence spectroscopy study -

The present study is aimed to analyze the speciation of the trivalent actinide ion Cm(III) in a system containing well characterized purified humic acid (Aldrich) and γ-Al2O3 by TRLFS. Accompanying sorption experiments (isotherms, pH-edges) were performed with Eu(III) and Am(III) to increase the range of metal ion concentration and to clarify the similarity of sorption properties of trivalent lanthanides and actinides. In order to obtain comprehensive spectroscopic information on Cm(III) speciation, the excitation spectrum is recorded in a range from λ = 370-400 nm. Fluorescence emission spectra obtained in an indirect excitation mode (λex = 355 nm) are compared to spectra appearing at direct Cm(III) excitation (λex = 396.6 nm). Only the HA bound Cm(III) is excited at λex = 355 nm due to the energy transfer proceeding from HA to complexed Cm(III). Direct excitation provides information on all fluorescing Cm(III) species in the system. (orig.)