Potential applications of nanostructured materials in nuclear waste management.

Abstract

This report summarizes the results obtained from a Laboratory Directed Research & Development (LDRD) project entitled "Investigation of Potential Applications of SelfAssembled Nanostructured Materials in Nuclear Waste Management". The objectives of this project are to (1) provide a mechanistic understanding of the control of nanometerscale structures on the ion sorption capability of materials and (2) develop appropriate engineering approaches to improving material properties based on such an understanding. 4 The project has been focused on two types of nanostructured materials: self-assembled mesoporous materials and layered double hydroxides. The major results are summarized below:• Acid-base titration experiments were performed on both mesoporous alumina and alumina particles under various ionic strengths. Under the same chemical conditions, the surface charge per mass on mesoporous alumina was as much as 45 times higher than that on alumina particles. This difference cannot be fully explained by the surface area difference between the two materials. The titration data have demonstrated that the nano-scale confinement has a significant effect, most likely via the overlap of the electric double layer (EDL), on ion sorption onto mesopore surfaces. This effect cannot be adequately modeled by existing surface complexation models, which were developed mostly for an unconfined solid-water interface.• As the pore size is reduced to a few nanometers, the difference between surface acidity constants (∆pK = pK 2 -pK 1 ) decreases, giving rise to a higher surface charge density on a nanopore surface than that on an unconfined mineral-water interface. The change in surface acidity constants results in a shift of ion sorption edges and enhances ion sorption on nanopore surfaces. Also, the water activity in a nanopore is greatly reduced, thus increasing the tendency for inner sphere complexation and mineral precipitation. All these effects combine to preferentially enrich trace elements in nanopores. This enrichment mechanism has a significant implication to many fundamental geochemical issues such as the irreversibility of ion sorption/desorption and the bioavailability of subsurface contaminants. The discovery of this mechanism provides a scientific basis for engineering high-performance ion adsorbents for nuclear waste management.• Layered double hydroxides (LDH) have shown a great promise for removing anionic contaminants. The anion sorption coefficients (K d ) have been measured for both activated and non-activated Mg-Al LDH materials. The activated material has a much higher anion sorption coefficient than the non-activated one, indicating that calcination can significantly improve anion sorption capacity of LDH. Sorption isotherms for Re and Se on the activated LDH material roughly follow the Freundlich isotherm, indicating the existence of various sorption sites with different sorption capabilities. Anions tend to first sorb on the external surface sites. As the anion concentration or the ionic strength ...

A Cationic Silver Pyrazine Coordination Polymer with High Capacity Anion Uptake from Water

“…Permanganate, perrhenate, and tetrafluoroborate were studied as initial examples. The latter was chosen as a comparative tetrahedral anion whereas permanganate and perrhenate were selected as group 7 surrogates for pertechnetate, which is a problematic radioactive pollutant during the vitrification of nuclear waste . An equimolar amount of permanganate and as-synthesized SPN were introduced into aqueous solution under mild stirring.…”

“…The latter was chosen as a comparative tetrahedral anion whereas permanganate and perrhenate were selected as group 7 surrogates for pertechnetate, which is a problematic radioactive pollutant during the vitrification of nuclear waste. 48 An equimolar amount of permanganate and as-synthesized SPN were introduced into aqueous solution under mild stirring. As monitored by UV−vis spectroscopy, the permanganate concentration rapidly decreased by 32% to 57% with reaction intervals of 0.5 to 3 h, respectively (Figure 10).…”