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

Li, Dien; Kaplan, Daniel I.; Price, Kimberly A.; Seaman, John C.; Roberts, Kimberly; Xu, Chen; Lin, Peng; Xing, Wei; Schwehr, Kathleen; Santschi, Peter H.

doi:10.1016/j.jenvrad.2019.106017

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

Journal Article · Wed Jul 17 00:00:00 EDT 2019 · Journal of Environmental Radioactivity

DOI:https://doi.org/10.1016/j.jenvrad.2019.106017· OSTI ID:1561205

Li, Dien ^[1]; Kaplan, Daniel I. ^[1]; Price, Kimberly A. ^[2]; Seaman, John C. ^[2]; Roberts, Kimberly ^[1]; Xu, Chen ^[3]; Lin, Peng ^[3]; Xing, Wei ^[3]; Schwehr, Kathleen ^[3]; Santschi, Peter H. ^[3]

Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)
Univ. of Georgia, Aiken, SC (United States)
Texas A & M Univ., Galveston, TX (United States)

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.