PNNL

Abstract

A prominent radionuclide of concern in nuclear wastes, 129I, is present in low-activity wastes (LAW) at the Hanford site. Several Ag-containing materials were tested as immobilization agents, or “getters”, for I (as iodide, I-) removal from deionized (DI) water and a liquid LAW simulant: Ag impregnated carbon (AgC), Ag exchanged zeolite (Ag-Z), and argentite. In anaerobic batch experiments with DI water, the AgC and argentite were most effective, with maximum Kd values of 6.2 × 105 mL/g for the Ag-C and 3.7 × 105 mL/g for the argentite after 15 d. Surface area and Ag content were found to influence the performance of the getters in DI water. In the anaerobic batch experiments with LAW simulant, Ag-Z vastly outperformed the other getters with Kd values of 2.4 × 103 mL/g at 2 h compared with 1.8 × 103 mL/g at 15 d by the argentite. All getters were stable over long periods of time (i.e., 40 d) in DI water, while the Ag-Z and argentite were also stable in the LAW simulant. Ag-Z was found to have consistent I removal upon crushing to a smaller particle size and in the presence of O2, making it a strong candidate for the treatment of LAW containing I and inclusion in low-temperature waste forms such as grouts.