Effect of solvents on the properties of Ag0-containing aluminosilicate sorbents for iodine capture

Radioiodine, which is generated during the reprocessing of nuclear fuel, must be immobilized on sorbents to convert it into a stable waste form. In this study, to capture iodine, Ag0-containing aluminosilicate sorbents (Ag0ASSs) were synthesized via sol-gel method using Na, Al, and Si alkoxides; co-solvent exchange; Ag/Na ion exchange; solvent exchange with solvents having different surface tensions; and ambient pressure drying. Three different Na+AlSi-OH sols were synthesized using sodium methoxide (NaOMe): aluminum tri-sec-butoxide [Al (OsBu)3]: tetraethyl orthosilicate (TEOS) with molar ratios of 1.05:1:1, 1.3:1.1:1, and 1.5:1.3:1. The solvent effect on textural properties such as surface area and pore size distribution, Ag0 particle size, and total iodine capture capacity of Ag0ASSs was investigated using two types of solvents: 1) a solvent with high surface tension (water) and 2) solvents with low surface tension (isopropanol and n-heptane). The textural properties and particle size distribution of Ag0 in the Ag0ASSs were dependent on the type of solvents used for exchange. The average pore diameter and cumulative pore volume of the Ag0ASSs, except the Brunauer-Emmett-Teller (BET) surface area, significantly increased with decreasing surface tension of solvent and increasing Al/Si atomic ratios. Although the increase in pore diameter and volume resulted in larger particle sizes of Ag0 in Ag0ASSs, the total and chemisorbed iodine-capture capacities of the Ag0ASSs increased. Therefore, the total and chemisorbed iodine -capture capacities depends on the pore size distributions of the Ag0ASSs. These Ag0ASSs have the potential to immobilize radioiodine, which could be further processed into stable compounds.