Immobilization of trivalent actinides by sorption onto quartz and incorporation into siliceous bulk:: Investigations by TRLFS

The adsorption of Cm(III) on quartz is studied by time resolved laser fluorescence spectroscopy (TRLFS) in the pH range from 3.75 to 9.45. The raw spectra are deconvoluted into three single components. The first one has a peak maximum at 593.8 nm and can be attributed to the Cm(III) aquo ion with an emission lifetime of 68 +/- 3 mu s. The second one corresponds to an adsorbed species and has a peak maximum at 601.4 nm and an emission lifetime of 123 +/- 10 mu s. The peak maximum of the third component is shifted to higher wavelength (603.6 nm) while the lifetime remains constant. Additionally, the adsorption of Am(III) on quartz is investigated in batch experiments. Based on the spectroscopic data a sorption mechanism is suggested. In addition, the obtained Am uptake data and the Cm-TRLFS data are modeled simultaneously using a single site Basic Stern model in combination with the charge distribution concept of Paulin,. The finally suggested model consists of two bidentate surface complexes where the second one is the product of hydrolysis of the first sorption species. In a separate set of experiments the influence of silicic acid at different concentrations on the Cm(III) speciation in a quartz system is investigated by TRLFS. In suspension silicic acid at low concentration (3.5 x 10(-4) mol/L) has no influence on the Cm(III) speciation. At high concentration (3.5 x 10(-2) mol/L) the Cm(III) speciation is definitely influenced. The results at higher concentration indicate the formation of Cm(III)/silicic acid complexes and the incorporation of Cm(III) into siliceous bulk. This is confirmed by measurements at a quartz single crystal surface. Moreover, these measurements indicate the formation of quartz/Cm(III)/silicic acid ternary complexes at the mineral surface. (c) 2007 Elsevier Inc. All rights reserved.