Details

Autor(en) / Beteiligte

• Saslow, Sarah A
• Kerisit, Sebastien N
• Varga, Tamas
• Mergelsberg, Sebastian T
• Corkhill, Claire L
• Snyder, Michelle M. V
• Avalos, Nancy M
• Yorkshire, Antonia S
• Bailey, Daniel J
• Crum, Jarrod
• Asmussen, R. Matthew

Titel

Immobilizing Pertechnetate in Ettringite via Sulfate Substitution

Ist Teil von

• Environmental science & technology, 2020-11, Vol.54 (21), p.13610-13618

Ort / Verlag

United States: American Chemical Society

Erscheinungsjahr

2020

Quelle

MEDLINE

Beschreibungen/Notizen

• Technetium-99 immobilization in low-temperature nuclear waste forms often relies on additives that reduce environmentally mobile pertechnetate (TcO4 –) to insoluble Tc­(IV) species. However, this is a short-lived solution unless reducing conditions are maintained over the hazardous life cycle of radioactive wastes (some ∼10,000 years). Considering recent experimental observations, this work explores how rapid formation of ettringite [Ca6Al2(SO4)3(OH)12·26­(H2O)], a common mineral formed in cementitious waste forms, may be used to directly immobilize TcO4 –. Results from ab initio molecular dynamics (AIMD) simulations and solid-phase characterization techniques, including synchrotron X-ray absorption, fluorescence, and diffraction methods, support successful incorporation of TcO4 – into the ettringite crystal structure via sulfate substitution when synthesized by aqueous precipitation methods. One sulfate and one water are replaced with one TcO4 – and one OH– during substitution, where Ca2+-coordinated water near the substitution site is deprotonated to form OH– for charge compensation upon TcO4 – substitution. Furthermore, AIMD calculations support favorable TcO4 – substitution at the SO4 2– site in ettringite rather than gypsum (CaSO4·2H2O, formed as a secondary mineral phase) by at least 0.76 eV at 298 K. These results are the first of their kind to suggest that ettringite may contribute to TcO4 – immobilization and the overall lifetime performance of cementitious waste forms.