November 3, 2020
Journal Article

Immobilizing Pertechnetate in Ettringite via Sulfate SUbstitution


Until recently, a nuclear waste form did not exist for the immobilization and long-term storage of the anionic form of radionuclide technetium-99 (99Tc), pertechnetate (TcO4-). Across international nuclear waste sites, the inability to capture TcO4- poses a threat to the local environment due to the anion’s long half-life and environmental mobility under environmentally oxic conditions. To combat this challenge, most waste forms would capture 99Tc using materials that reduce TcO4- to Tc(IV) species, e.g. 99Tc oxides or 99Tc sulfides. However, this is a short-lived solution unless reducing capacities can be regenerated to last over the long life expectancy of some nuclear waste forms (~10,000 years). In light of recent experimental observations gained from the development of cementitious waste forms and unconfirmed hypotheses from the literature, this work explores how ettringite, a common mineral formed in cementitious materials with demonstrated success in incorporating oxyanions, may be used to immobilize TcO4- directly and over the life-time of the waste form. Using batch precipitation experiments, solid phase characterization techniques, and ab initio molecular dynamics simulations, we demonstrate herein successful incorporation of TcO4- into ettringite via substitution for SO42- within the ettringite crystal structure. These results are first of their kind and confirm the hypothesis that ettringite acts as an immobilizing mineral within cementitious waste forms for the highly mobile TcO4- oxyanion, enhancing the overall performance of these waste forms over time.

Revised: November 16, 2020 | Published: November 3, 2020


Saslow S.A., S.N. Kerisit, T. Varga, S.T. Mergelsberg, C.L. Corkhill, M. Snyder, and N.M. Avalos, et al. 2020. "Immobilizing Pertechnetate in Ettringite via Sulfate SUbstitution." Environmental Science & Technology 54, no. 21:13610–13618. PNNL-SA-147963. doi:10.1021/acs.est.0c03119