SREL Reprint #3576

Iodine immobilization by silver-impregnated granular activated carbon in cementitious systems

Dien Li1, Daniel I. Kaplan1, Kimberly A. Price2, John C. Seaman2, Kimberly Roberts1, Chen Xu3,
Peng Lin3, Wei Xing3, Kathleen Schwehr3, and Peter H. Santschi3

1Savannah River National Laboratory, Aiken, SC, 29808, United States
2Savannah River Ecology Laboratory, University of Georgia, Aiken, SC, 29802, United States
3Department of Marine Science, Texas A & M University at Galveston, Galveston, TX, 77553, United States

Abstract: Silver (Ag)-based technologies are amongst the most common approaches to removing radioiodine from aqueous waste streams. As a result, a large worldwide inventory of radioactive AgI waste presently exits, which must be stabilized for final disposition. In this work, the efficacy of silver-impregnated granular activated carbon (Ag-GAC) to remove iodide (I-), iodate (IO3-) and organo-iodine (org-I) from cementitious leachate was examined. In addition, cementitious materials containing I-, IO3-, or org-I loaded Ag-GAC were characterized by iodine K-edge XANES and EXAFS to provide insight into iodine stability and speciation in these waste forms. The Ag-GAC was very effective at removing I- and org-I, but ineffective at removing IO3- from slag-free grout leachate under oxic conditions. I- or org-I removal was due to the formation of insoluble AgI(s) or Ag-org-I(s) on the Ag-GAC. When I--loaded Ag-GAC material was cured with slag-free and slag grouts, I- was released from AgI(s) to form a hydrated I- species. Conversely, when org-I loaded Ag-GAC material was cured in the two grout formulations, no change was observed in the iodine speciation, indicating the org-I species remained bound to the Ag. Because little IO3- was bound to the Ag-GAC, it was not detectable in the grout. Thus, grout formulation and I speciation in the waste stream can significantly influence the effectiveness of the long-term disposal of radioiodine associated with Ag-GAC in grout waste forms.

Keywords: Iodine speciation; Cement; Slag; Immobilization; Redox; Silver-impregnated granular activated carbon

SREL Reprint #3576

Li, D., D. I. Kaplan, K. A. Price, J. C. Seaman, K. A. Roberts, C. Xu, P. Lin, W. Xing, K. A. Schwehr, and P. H. Santschi. 2019. Iodine immobilization by silver-impregnated granular activated carbon in cementitious systems. Journal of Environmental Radioactivity 208-209(2019): Article 106017.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).