Functionalized Organoclays for Increased Tc and I Sequestration

Nuclear energy production is a promising process for sustainable energy due to its relatively small carbon footprint and low carbon emission. However, the containment of highly mobile isotopes in nuclear waste such as technetium and iodine presents environmental challenges. Therefore, it is imperative to design new buffer materials to immobilize radionuclides to prevent waste from entering water streams. Organoclays, organically modified clays, are promising material systems for sequestration of radionuclides. Focusing on alkyl amine-based modifications, we have recently examined the role of carbon chain length and number of chains on the structure and Tc removal performance for montmorillonite. We will show that Tc removal performance and affinity are increased for longer chains and a greater number of chains. Functionalization with an 8-carbon chain length amine with 2 long chains shows a Tc removal > 90% and K_d of 4700 ± 300 mL/g while a single 8-carbon chain length amine shows < 10% removal and K_d of 10 ± 3 mL/g. Additionally, we will show that the performance of amine functionalized clays can be increased by additional functionalization with a cation such as Fe. For example, montmorillonite modified with a single 16-carbon chain length amine shows a Tc removal of just ~ 40% while the addition of Fe increases the removal to ~ 75%. We will demonstrate that these performance increases correlate with structural changes in the functionalized clays captured via Fourier-transform infrared spectroscopy (FTIR) and x-ray diffraction (XRD). Specifically, as the clay’s basal plane spacing is increased, the Tc removal performance is also increased and there are associated changes in the orientation and structure within the interlayer of the clay. To better understand the separate effect of the organic and cation modifications on sequestration performance, we will also show the performance in zirconium and amine functionalized clays focusing on the basal plane spacing and CH₂ vibrational bands as a function of concentration.