Evaluation of materials for iodine and technetium immobilization through sorption and redox-driven processes

• Published in: The Science of the total environment Vol. 716; no. C; p. 136167
• Main Authors: Pearce, Carolyn I., Cordova, Elsa A., Garcia, Whitney L., Saslow, Sarah A., Cantrell, Kirk J., Morad, Joseph W., Qafoku, Odeta, Matyáš, Josef, Plymale, Andrew E., Chatterjee, Sayandev, Kang, Jaehyuk, Colon, Ferdinan Cintron, Levitskaia, Tatiana G., Rigali, Mark J., Szecsody, Jim E., Heald, Steve M., Balasubramanian, Mahalingam, Wang, Shuao, Sun, Daniel T., Queen, Wendy L., Bontchev, Ranko, Moore, Robert C., Freedman, Vicky L.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 10.05.2020; Elsevier
• Subjects: aerobic conditions; anion exchange resins; bismuth; Bismuth-based materials; coordination polymers; environmental impact; ferrihydrite; groundwater; half life; Iodate; iodates; iodine; iron; Iron oxides; Layered double hydroxides; Metal organic frameworks; Pertechnetate; redox reactions; risk; scanning electron microscopy; sorbents; sorption; sulfides; technetium; toxicity; X-radiation; X-ray absorption spectroscopy; Iodate; Bismuth-based materials; Metal organic frameworks; Iron oxides; Pertechnetate; Layered double hydroxides
• ISSN: 0048-9697; 1879-1026; 1879-1026
• DOI: 10.1016/j.scitotenv.2019.136167

Radioactive iodine-129 (129I) and technetium-99 (99Tc) pose a risk to groundwater due to their long half-lives, toxicity, and high environmental mobility. Based on literature reviewed in Moore et al. (2019) and Pearce et al. (2019), natural and engineered materials, including iron oxides, low-solubility sulfides, tin-based materials, bismuth-based materials, organoclays, and metal organic frameworks, were tested for potential use as a deployed technology for the treatment of 129I and 99Tc to reduce environmental mobility. Materials were evaluated with metrics including capacity for IO3− and TcO4− uptake, selectivity and long-term immobilization potential. Batch testing was used to determine IO3− and TcO4− sorption under aerobic conditions for each material in synthetic groundwater at different solution to solid ratios. Material association with IO3− and TcO4− was spatially resolved using scanning electron microscopy and X-ray microprobe mapping. The potential for redox reactions was assessed using X-ray absorption near edge structure spectroscopy. Of the materials tested, bismuth oxy(hydroxide) and ferrihydrite performed the best for IO3−. The commercial Purolite A530E anion-exchange resin outperformed all materials in its sorption capacity for TcO4−. Tin-based materials had high capacity for TcO4−, but immobilized TcO4− via reductive precipitation. Bismuth-based materials had high capacity for TcO4−, though slightly lower than the tin-based materials, but did not immobilize TcO4− by a redox-drive process, mitigating potential negative re-oxidation effects over longer time periods under oxic conditions. Cationic metal organic frameworks and polymer networks had high Tc removal capacity, with TcO4− trapped within the framework of the sorbent material. Although organoclays did not have the highest capacity for IO3− and TcO4− removal in batch experiments, they are available commercially in large quantities, are relatively low cost and have low environmental impact, so were investigated in column experiments, demonstrating scale-up and removal of IO3− and TcO4− via sorption, and reductive immobilization with iron- and sulfur-based species. [Display omitted] •129I and 99Tc are a risk to groundwater due to toxicity, long half-life, and mobility.•Natural and engineered materials were tested for potential to reduce mobility.•Bismuth oxy(hydroxide) was the most promising material for iodate immobilization.•Anion-exchange resins outperformed all materials for pertechnetate sorption.•Immobilization capacity of material depends on uptake mechanism and reaction product.