PNNL

Abstract

In this study, silver-containing xerogel (Ag-Xero), faujasite (Ag-FAU) zeolite, and Ag-mordenite (Ag-MOR) zeolite sorbents were loaded with iodine gas [I2(g)] under saturated conditions at 150°C for 24 hours followed by densification and consolidation into monolithic waste forms using spark plasma sintering (SPS). For the Ag-Xero materials, some pellets were made with as-loaded powders, and some were made with preheated (PH = 500°C for 30 min) powders. The SPS processing was conducted at 50 MPa under different temperatures (T = 200–800°C) for different times (t = 0.5–30 min) so that the properties of the products could be evaluated and compared where eleven AgI-Xero samples, five AgI-FAU, and two AgI-MOR separate samples were produced. The Ag-Xero showed notably higher iodine loadings (qe = 470 mg g-1) than the Ag-FAU (qe = 368 mg g-1) and Ag-MOR (qe = 108 mg g-1). Iodine concentrations in SPS-processed pellets were highest in AgI-Xero samples without PH followed by AgI-Xero (PH) samples, AgI-FAU samples, and then AgI-MOR samples. Silver utilization (AgU = I/Ag on an mol% basis) values were in the order of AgI-MOR ~ AgI-Xero (no PH) > AgI-Xero (PH) > AgI-FAU. Chemical durabilities of the AgI-Xero (PH) pellets were very favorable with lower releases than SPS pellets made from AgI-Xero samples without the PH. These results show promise for an alternate method than hot isostatic pressing to make high density monolithic iodine waste forms for long-term disposal.