(505c) Uranium Adsorption from Seawater By Amidoxime-Functionalized Polyethylene Fibers: Modeling and Experiments
At a concentration or 3.3 ppb, uranium in seawater can become a valuable resource for future nuclear energy. This goal can be realized by developing cost-effective methods for extracting uranium from seawater. Based on recent work in Japan, Europe, and the U.S., a cost-effective approach should include development of a highly selective adsorbent of relatively high uranium capacity, on the order of 4-10 g U/kg-adsorbent that can be recycled over six times during its lifetime. The adsorbent has to work in a passive mode, taking advantage of the flow of seawater currents. Progress toward the development of such adsorbent will be reported in this presentation. Hollow, high-surface-area polyethylene fibers grafted with amidoxime ligands have shown a uranium capacity over 4 g U/kg-adsorbent in experiments with natural seawater. Attempts to optimize the adsorbent performance during the synthesis and conditioning steps will be discussed. Efforts to understand the adsorption mechanisms include spectroscopic characterization and transport and reaction-kinetic modeling. FTIR and NMR spectra are obtained to determine the reaction mechanism, which is still not fully understood. In earlier modeling work, we have shown that, under some circumstances, uranium uptake from seawater by amidoxime-based adsorbent is reaction limited due to the presence of carbonate ions which compete with amidoxime. In other circumstances, transport effects become important. A current modeling effort includes both transport and kinetic mechanisms to describe uranium uptake by single-adsorbent fibers and adsorbent braids.