A luminescence line-narrowing spectroscopic study of the uranium(VI) interaction with cementitious materials and titanium dioxide.

Jan Tits,Thorsten Stumpf,Clemens Walther,Erich Wieland,Nathalie Macé

doi:10.1039/c4dt02172j

Abstract

Non-selective luminescence spectroscopy and luminescence line-narrowing spectroscopy were used to study the retention of UO2(2+) 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 UO2(2+) bonding environment. This problem was largely overcome by using luminescence line-narrowing spectroscopy. This technique allowed unambiguous identification of three different types of UO2(2+) sorbed species on C-S-H phases and HCP. Comparison with spectra of UO2(2+) 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 UO2(2+) 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.

Highlights

Cementitious materials are commonly used worldwide for the solidification of low- and intermediate level radioactive waste (L/ILW) prior to storage in surface or deep geological repositories.1,2 For an accurate prediction of the long term fate of this radioactive waste, a comprehensive understanding of the chemical interactions of the radionuclides present in the waste with the solidification material is essential
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)
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

Summary

Introduction

Cementitious materials are commonly used worldwide for the solidification of low- and intermediate level radioactive waste (L/ILW) prior to storage in surface or deep geological repositories. For an accurate prediction of the long term fate of this radioactive waste, a comprehensive understanding of the chemical interactions of the radionuclides present in the waste with the solidification material is essential. Calcium silicate hydrates (C-S-H) are major constituents of cementitious materials They have a tobermorite-like layered structure consisting of Ca–O sheets linked on each side to silicate chains in a “dreierkette” arrangement.. Several studies have found experimental evidence for the incorporation of trivalent and tetravalent actinides and lanthanides by substitution for Ca in the interlayers and the Ca–O layer of C-S-H phases.. Several studies have found experimental evidence for the incorporation of trivalent and tetravalent actinides and lanthanides by substitution for Ca in the interlayers and the Ca–O layer of C-S-H phases.5–9 It is still an open question whether or not larger actinyl ions such as UO22+ exhibit similar incorporation behaviour Several studies have found experimental evidence for the incorporation of trivalent and tetravalent actinides and lanthanides by substitution for Ca in the interlayers and the Ca–O layer of C-S-H phases. It is still an open question whether or not larger actinyl ions such as UO22+ exhibit similar incorporation behaviour

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