Determination of uranium(VI) sorbed species in calcium silicate hydrate phases: a laser-induced luminescence spectroscopy and batch sorption study.

Batch sorption experiments and time-resolved luminescence spectroscopy investigations were carried out to study the U(VI) speciation in calcium silicate hydrates for varying chemical conditions representing both fresh and altered cementitious environments. U(VI) uptake was found to be fast and sorption distribution ratios (R(d) values) were very high indicating strong uptake by the C-S-H phases. In addition a strong dependence of pH and solid composition (Ca:Si mol ratio) was observed. U(VI) luminescence spectroscopy investigations showed that the U(VI) solid speciation continuously changed over a period up to 6 months in contrast to the fast sorption kinetics observed in the batch sorption studies. Decay profile analysis combined with factor analysis of series of spectra of U(VI)-C-S-H suspensions, recorded with increasing delay times, revealed the presence of four luminescent U(VI) species in C-S-H suspensions, in agreement with the batch sorption data. Along with the aqueous UO(2)(OH)(4)(2-) species and a Ca-uranate precipitate, two different sorbed species were identified which are either bound to silanol groups on the surface or incorporated in the interlayer of the C-S-H structure.