BISMUTH-FUNCTIONALIZED SORBENTS FOR RADIOIODINE CAPTURE
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Authors
Baskaran, Karthikeyan
Issue Date
2023
Type
Dissertation
Language
Keywords
Aerogel , Functionalization , Iodine , Xerogel
Alternative Title
Abstract
The soybean oil was used as a porogen to tailor porestructure of gels made with tetraethoxysilane (TEOS) and TEOS + methyltrimethoxysilane (MTMS) silica precursor. Oil concentrations of 9.09 v/v% and 33.33 v/v% were studied. The miscibility of the oil and precursor decreased as the silica gel network formed, leading to oil-rich regions within the silica matrix. Upon removal of oil, oil rich regions form a macroscale pore. Solvent exchange and calcination were performed to remove oil from silica xerogels. TEOS precursor gave isolated but larger pores while TEOS + MTMS precursor gels gave finer and interconnected pores. As a result of finer pore structure gels made with TEOS+MTMS have a higher surface area of 1068 ± 113 m2g-1. Bismuth nanoparticles were loaded into silica xerogel during the sol-gel process and its iodine capture performance was evaluated. Xerogel made with porogens captured more iodine (526 ± 31 mg g-1) compared to xerogel without porogen of same bismuth loading level (359 ± 53 mg g-1). The bismuth loaded xerogels were aged in an oxidizing atmosphere using 1% NO2 gas before and after iodine capture. Xerogel showed gradual decline in iodine capture with longer aging time and performed better when compared to free standing nanoparticles, suggesting the protective action of surrounding xerogel. After aging, 82 mass% of the Bi-NPs were converted to Bi2O3 with only a small amount of iodine captured as BiOI (18 mass%). After aging TEO-5 for 3 h, iodine was captured as both BiI3 (26%) and BiOI (74%) and no Bi2O3 was detected. The iodine captured sorbents were leached with water to simulate a flooded situation. A steady increase in iodine concentration was observed until all nanoparticles were converted to bismuth oxy iodide, a water insoluble compound. Carbon foam loaded with bismuth nanoparticle through electrodeposition was studied as an alternative to silica sorbents. Alternative to silica xerogel is required as humid off-gas stream as seen in Hanford legacy waste processing plant can degrade the xerogel. Carbon foam without bismuth loading showed equal amount of physisorption to chemisorption. The Quantity of iodine adsorbed as chemisorbed iodine compound increased with bismuth loading level. The particle size influenced the quantity of iodine captured per unit mass of sorbent as iodine diffusion in bismuth is limited. The highest iodine loading of 953.0 ± 20 mg g�"1 was achieved with bismuth loaded carbon foam. Overall, the experiments discussed in this dissertation demonstrate the potential of using different material and approaches to manufacture the materials for the capture of radioactive iodine from oxidizing off-gas stream. These findings could have implications for improving human health and environmental safety in the reprocessing of used nuclear fuel and processing legacy nuclear waste.
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Creative Commons Attribution-NonCommercial 4.0 United States