Resource extraction – Sorbent considerations

1. Resource extraction – Sorbent considerations In order to process the huge volumes of water necessary to recover U at the ppb level, it will be energetically necessary to utilize the ocean currents to move large volumes of water through the sorbent beds. On-shore processing of the laden sorbent means that the sorbent beds will have to be periodically transported to the processing plant, therefore the bulk (both weight and volume) of the sorbent material will be very important. Therefore, the sorbent bed will need to be designed around a nanoporous sorbent material with high functional density in order to maximize resource extraction efficiency and to minimize transportation costs. Chemical selectivity and ease of regeneration (stripping) of the nanoporous sorbent will be very important design features, as both will have a direct impact on the efficiency of the extraction process. Rigid nanoporous architecture prevents microbial access inside the pores, while maintaining free access to dissolved chemical species. Given the long-term exposure to ocean water, sorbents that are resistant to bio-fouling will be advantageous (and will undoubtedly save energy in the regeneration/stripping stage). Polymer-based sorbents may not be viable in this application due to fouling problems, swelling, and microbial degradation (depolymerization).

2. Functional nanoporous sorbents High functional density translates to minimal sorbent bed volume. High binding capacity comes from the marriage of the extremely high surface area and dense surface coverage. Fast sorption kinetics arise from the rigid, open pore structure. Chemical specificity dictated by monolayer interface – ligand field can be easily tailored for specific targets (in this case U). Existing expertise in actinide capture from natural waters (including sea water). Small pores prevent microbial access. Large particle size (many 10s of microns) are easily handled/packaged/processed. “Environmental and Sensing Applications of Molecular Self-Assembly” in “Encyclopedia of Nanoscience and Nanotechnology”; Dekker, 2004, pp. 1135-1145.

3. Examples of how nanoporous sorbents can be tailored for specific targets Env. Sci. & Tech. 2001, 35, 3962-3966. Chemistry of Materials 1999, 11, 2148-2154 J. Physical. Chem. B. 2001, 105, 6337-6346. J. Synchrotron Radiation, 2001, 8, 922-924 Cu-EDA Radiochimica Act 2003, 91, 539-545 Cu-FC-EDA Cs Env. Sci. & Tech. 2005, 39, 1324-1331 . Env. Sci. & Tech. 2005, 39, 1332-1337 . J. Materials Chemistry 2004, 14, 3356-3363 Chem. Comm. 2002, 1374-1375. Thiol Science, 1997, 276, 923-926. J. Synchrotron Radiation, 1999, 6,633-635 Sep. Sci. & Technol. 1999, 3411, 2329-2345 Mat. Tech. Adv. Perf. Mat. 1999, 14, 183-193 Surf. Sci. & Catalysis, 2000, 105, 729-738. ….all by varying the monolayer ligand field. HOPO Prop-Phos J. Mater. Chem.2007, 17, 2863-2874.

4. Key issues, new directions, science questions Existing methods are based on polymer fibers. Need to increase functional density of sorbent. Amidoximes have been popular for this chemistry, but which ligands are really best? New U-selective ligands have come along that are probably better. What is the best way to present these sorbents in a marine environment? Actual marine testing is critical for success. Biofouling will be an issue. How do we best address/mitigate this issue? Packaging of the sorbent bed will be key. How extensive is the regeneration processing required by a candidate sorbent? We want to make this as simple (and as sustainable) as possible. How many regen cycles can the sorbent realistically withstand? Life cycle costs drop with each additional regen cycle.