Iodine Capture with Mechanically Robust Heat-Treated Ag–Al–Si–O Xerogel Sorbents

High Resolution Image Download MS PowerPoint Slide Various radionuclides are released as gases during reprocessing of used nuclear fuel or during nuclear accidents including iodine-129 ( 129 I) and iodine-131 ( 131 I). These isotopes are of particular concern to the environment and human health as they are environmentally mobile and can cause thyroid cancer. In this work, silver-loaded heat-treated aluminosilicate xerogels (Ag-HTX) were evaluated as sorbents for iodine [I 2(g) ] capture. After synthesis of the base NaAlSiO 4 xerogel, a heat-treatment step was performed to help increase the mechanical integrity of the NaAlSiO 4 gels (Na-HTX) prior to Ag-exchanging to create Ag-HTX xerogels. Samples were characterized by powder X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, Brunauer–Emmett–Teller analysis, gravimetric iodine loading, nanoindentation, and dynamic mechanical analysis. The structural and chemical analyses of Ag-HTX showed uniform distribution of Ag throughout the gel network after Ag-exchange. After I 2(g) capture, the AgI crystallites were observed in the sorbent, verifying chemisorption as the primary iodine capture mechanism. Iodine loading of this xerogel was 0.43 g g –1 at 150 °C over 1 day and 0.52 g g –1 at 22 °C over 33 days. The specific surface area of Ag-HTX was 202 m 2 g –1 and decreased to 87 m 2 g –1 after iodine loading. The hardness of the Na-HTX was >145 times higher than that of the heat-treated aerogel of the same starting composition. The heat-treatment process increased Young’s modulus (compressive) value to 40.8 MPa from 7.0 MPa of as-made xerogel, demonstrating the need for this added step in the sample preparation process. These results show that Ag-HTX is a promising sorbent for I 2(g) capture with good iodine loading capacity and mechanical stability.