Functionalized Clays for Radionuclide Sequestration: A Review

Abstract

Performance assessment of nuclear waste disposal options requires implementation of effective buffer materials. Buffer materials must meet longevity requirements and scavenge challenging radioisotopes, e.g., iodine-129 (I-129) and technetium-99 (Tc-99), both long-lived, highly mobile, anionic species in oxic environments. In many proposed nuclear waste repositories, heat generating radioactive waste will be surrounded by clay buffer material, which swells to fill the gap between the waste package and the host geology, restricting radionuclide transport to diffusive processes for several hundred years. The clay can be functionalized to further the limit release of Tc-99, as pertechnetate (TcO 4 − ), and I-129, as iodate (IO 3 − ) and iodide (I − ). Here, we review clay buffer functionalization and the potential to enhance sequestration of anionic radionuclides that have an increased risk of leaching out of a disposal facility. Functionalization with quaternary amines, nanosilver, bismuth-based materials, silane, and aluminum pillars have been demonstrated to improve the removal of targeted contaminants from solution. This review defines key research questions that remain: (i) can functionalized clay immobilize TcO 4 − , IO 3 − , and I − to the same extent as the reactive components themselves? (ii) Does functionalization affect the ability of the clay barrier to perform its safety functions of protecting the waste canister and limiting radionuclide transport? In addition to radionuclide retention, a multimodal analytical approach is required to assess functionalized clay performance, and recommended techniques are reviewed here. The key parameters that can influence radionuclide sequestration by functionalized clay are also evaluated. Theoretical approaches, including both density functional theory calculations and molecular dynamics simulations, can inform the energetics and kinetics of radionuclide interactions with functionalized clays. This combined experimental and theoretical approach can link atomistic and microscopic processes to predict the macroscopic physical properties of the functionalized clays.

Preparation and properties of vermiculite modified by triphenylbutylphosphonium bromide and PBAT composite film

“…Compared with quaternary ammonium salts of the same molecular structure, quaternary phosphonium salts are easier to synthesize, have higher heat resistance, lower liquid crystal state onset temperature and wider liquid crystal phase temperature interval 16–18 . They are more and more popular among researchers because their thermal degradation temperature is above 300°C and they do not thermally degrade when used to modify polymer materials, which is more conducive to improving the thermal stability of materials 19–22 . However, foreign reports on their specific synthesis methods are incomplete, 23 and domestic research is also immature, so the synthesis methods need to be explored in terms of reaction conditions and reaction solvents.…”

“…[16][17][18] They are more and more popular among researchers because their thermal degradation temperature is above 300 C and they do not thermally degrade when used to modify polymer materials, which is more conducive to improving the thermal stability of materials. [19][20][21][22] However, foreign reports on their specific synthesis methods are incomplete, 23 and domestic research is also immature, so the synthesis methods need to be explored in terms of reaction conditions and reaction solvents.…”

Influence of Interfering Ions and Adsorption Temperature on Radioactive Iodine Removal Efficiency and Stability of Ni-MOF-74 and Zr-UiO-66

“…The build-up concentration of carbonate ions in the solution caused by its relatively high steric hinderance (bulkiness) increases the iodide ions flux towards the active sites of the MOF, thereby increasing the iodine update in the presence of CO 3 2– . The electronegativities of the elements that are contained in the three anion groups are listed in ascending order C ∼ I ≪ Cl < O. − Combining the aforementioned effects of CO 3 2– and Cl – on the uptake of I – , a solution of these three anions was prepared and their combined effects were studied accordingly. Figure revealed that the adsorption of I – in the Cl – and CO 3 2– containing solution was much more effective compared to a solution containing only iodide ion.…”

Strontium and Cesium Adsorption on Exopolysaccharide-Modified Clay Minerals

“…40,41,43 On the one hand, there should be the presence of substances with an amorphous structure 43 and/or the formation of a disordered pillared structure, 7 which was confirmed by SEM characterization (discussed below, Figure 5a,f), and was consistent with the basal spacing. On the other hand, the inner-sphere complexation may occur between fully or partially dehydrated Cs and the more durable siloxane groups where Cs irreversibly bound between the upper and lower tetrahedral sheets, resulting in collapsing interlayers 6,44,45 It was also shown in AFM (Figure 6f) that the distinct columnar, as well as the uniform, rounded, and thick structures appeared. Benedicto et al 46 also found that the interlayer of illite collapsed after it adsorbed the Cs ion.…”