Sorption of Cm(III) onto different Feldspar surfaces: a TRLFS study

Summary

The pH dependent sorption of Cm(III) onto alkali Feldspars (albite and orthoclase) is investigated by time resolved laser fluorescence spectroscopy (TRLFS) in the pH range from 3.4 to 9.4. Three single components are calculated from the raw spectra for both feldspar systems. The first component which corresponds to the Cm(III) aquo ion has a peak maximum at 593.8 nm and a fluorescence emission lifetime of 68±4 μs. This lifetime corresponds to a Cm(III) coordination of nine water molecules in the first coordination sphere of the actinide ion. The second component with a peak maximum at 601.4 nm corresponds to an adsorbed species. Its lifetime of 107±3 μs indicates a reduction of coordinating H₂O/OH⁻ ligands from nine to five caused by inner-sphere complex formation. The third component (603.6 nm) can be attributed to another sorption species. The corresponding lifetime is again 107±3 μs. Hence the number of coordinating ligands remains constant while the ligand field changes caused by the hydrolysis of the sorbed Cm(III).

In a further set of experiments the Cm(III) sorption onto albite which is altered at pH 6.0 and pH 9.0 is also investigated by TRLFS. Independent of the dissolution and different surface morphologies caused by the alteration process the same Cm(III) species are formed as found for the sorption onto the untreated albite surface. With regard to the clarification of a feldspar dissolution mechanism the TRLFS results of the Cm(III) sorption onto altered feldspar surfaces give no evidence for a dissolution-reprecipitation based alteration mechanism.