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

• DOI: 10.1016/j.scitotenv.2019.136167
• Publication Date: 2019-12-18T10:23:01Z
• Authors: Carolyn I. Pearce; Elsa A. Cordova; Whitney L. Garcia; Sarah A. Saslow; Kirk J. Cantrell; Joseph W. Morad; Odeta Qafoku; Josef Matyáš; Andrew E. Plymale; Sayandev Chatterjee; Jaehyuk Kang; Ferdinan Cintron ...; Tatiana G. Levits...; Mark J. Rigali; Jim E. Szecsody; Steve M. Heald; Mahalingam Balasu...; Shuao Wang; Daniel T. Sun; Wendy L. Queen; Ranko Bontchev; Robert C. Moore; Vicky L. Freedman
• Keywords: i-129; bismuth-based materials; pertechnetate; iron oxides; sediments; layered double hydroxides; 01 natural sciences; 6. Clean water; metal organic frameworks; iodate; 13. Climate action; groundwater; 0105 earth and related environmental sciences

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.