Uranium from Seawater Marine Testing Program at the University of Miami's Broad Key Island Research Station
Marine testing at Broad Key Island (BKI), Florida was conducted to validate adsorption capacity and adsorption kinetics results obtained for several formulations of the ORNL amidoxime-based polymeric adsorbents in Sequim Bay, Washington in another location with different oceanographic and water quality conditions (e.g. temperature, dissolved organic carbon, salinity and trace element content). Broad Key is a small island off the southeast coast of Florida at the southern end of Biscayne Bay. Flow-through column and recirculating flume experiments were conducted at BKI using ambient filtered seawater and identical exposure systems as were used at the Pacific Northwest National Laboratory’s (PNNL) Marine Sciences laboratory (MSL). Testing was conducted in two periods in FY 2015 and FY 2016 with five different amidoxime-based adsorbent materials, four produced by ORNL (AF1, AI8, AF8, and AF1-DMSO) and one by LCW technologies (LCW-10). All exposures were conducted at ambient seawater temperatures, with moderate temperature control on the ambient seawater to mitigate large daily swings in the seawater temperature. The ORNL adsorbents AF1, AI8 and AF1-AO-DMSO all had fairly similar adsorption capacities (6.0 to 6.6 g U/ kg adsorbent) after 56 days of exposure at ambient temperature (26 to 31 °C) and salinity (35.7 to 37.4), but the AF8 adsorbent was considerably lower at 4.4 g U/kg adsorbent. All the adsorbents tested at BKI had higher capacities than was observed at PNNL, with the higher temperatures likely a major factor contributing to this difference. In general, the elemental distribution (expressed as a relative percentage) on all the adsorbents agreed well, including good agreement with the elemental distribution pattern for AF1 adsorbent exposed at PNNL. The most notable exception to a uniform elemental distributional pattern across the various adsorbents occurs with vanadium. The relative mass percentage for vanadium retained by the adsorbents ranged from a minimum of 13% for the AF8 formulation to a maximum of 29% for the AI8 formulation. All the V/U mass ratios at BKI are lower than observed for the AF1 adsorbent at PNNL (3.0). Temperature likely plays a significant role in the V/U mass ratio difference between BKI and PNNL. Because uranium has a higher adsorption capacity at higher temperatures, one would expect that warmer exposures would favor a lower V/U mass ratio, which could explain why the V/U mass ratio for the PNNL exposures are higher than observed for the BKI exposures. Marine Testing at BKI offers the opportunity to test adsorbent performance under warmer ambient and more saline conditions than exist at the marine test site on Sequim Bay. This is particularly important since the amidoxime-based adsorbents respond strongly to temperature. In addition, since salinities are about 15% higher at BKI compared to Sequim Bay (36 vs. 31), uranium adsorption capacities are about 15% higher at the BKI site compared to Sequim Bay.