Encapsulation of iodine-loaded metallated silica materials by a geopolymer matrix

The development of a wasteform for the disposal of I-129 would enable a change in waste management of iodine from recycling of nuclear fuel. Initial results investigating the encapsulation of iodide-loaded metallated silica sorbents into a geopolymer matrix are presented. Two silica materials, with a mercapto and a thiourea functionality, were found in scoping trials to have modest iodide loading capacities [72.9 ± 5 mg(I)/g, 119.5 ± 5 g(I)/g]]. Loaded sorbents were encapsulated in a geopolymer (GP) matrix at a conservative 2 wt% loading of capture material to test whether a wasteform could be created. A Blast Furnace Slag:Portland Cement (BFS:PC) cement was created as a benchmark reference. Successful formation of both BFS:PC and GP wasteforms was achieved, but the silica matrix in the GP samples was found to break down due to the high pH (~ 14) of the fresh geopolymer paste. Bleed water from one of the GP samples was analysed showing formation of Ag2S.