A luminescence line-narrowing spectroscopic study of the uranium(vi) interaction with cementitious materials and titanium dioxide†
Non-selective luminescence spectroscopy and luminescence line-narrowing spectroscopy were used to study the retention of UO22+ on titanium dioxide (TiO2), synthetic calcium silicate hydrate (C-S-H) phases and hardened cement paste (HCP). Non-selective luminescence spectra showed strong inhomogeneous line broadening resulting from a strongly disordered UO22+ bonding environment. This problem was largely overcome by using luminescence line-narrowing spectroscopy. This technique allowed unambiguous identification of three different types of UO22+ sorbed species on C-S-H phases and HCP. Comparison with spectra of UO22+ sorbed onto TiO2 further allowed these species to be assigned to a surface complex, an incorporated species and an uranate-like surface precipitate. This information provides the basis for mechanistic models describing the UO22+ sorption onto C-S-H phases and HCP and the assessment of the mobility of this radionuclide in a deep geological repository for low and intermediate level radioactive waste (L/ILW) as this kind of waste is often solidified with cement prior to storage.