Competitive TcO4 –, IO3 –, and CrO4 2– Incorporation into Ettringite

• Published in: Environmental science & technology 2021-01, Vol.55 (2), p.1057-1066
• Main Authors: Gillispie, Elizabeth C, Mergelsberg, Sebastian T, Varga, Tamas, Webb, Samuel M, Avalos, Nancy M, Snyder, Michelle M. V, Bourchy, Agathe, Asmussen, R. Matthew, Saslow, Sarah A
• Format: Article
• Language: English
• Subjects: Contaminants in Aquatic and Terrestrial Environments
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/acs.est.0c06707

Ettringite is a naturally occurring mineral found in cementitious matrices that is known for its ability to incorporate environmentally mobile oxyanion contaminants. To better assess this immobilization mechanism for contaminants within cementitious waste forms intended for nuclear waste storage, this work explores how mixed oxyanion contaminants compete for ettringite incorporation and influence the evolving mineralogy. Ettringite was precipitated in the presence of TcO4 –, IO3 –, and/or CrO4 2–, known contaminants of concern to nuclear waste treatment, over pre-determined precipitation periods. Solution analyses quantified contaminant removal, and the collected solid was characterized using bulk and microprobe X-ray diffraction coupled with pair distribution function and microprobe X-ray fluorescence analyses. Results suggest that ≥96% IO3 – is removed from solution, regardless of ettringite precipitation time or the presence of TcO4 – or CrO4 2–. However, TcO4 – removal remained