Uranium from Seawater Marine Testing Program at the University of Miami’s Broad Key Island Research Station

Abstract

Marine testing at Broad Key Island (BKI), FL was conducted to validate adsorption capacity and adsorption kinetics results obtained for several formulations of the ORNL amidoxime-based polymeric adsorbents in Sequim Bay, WA 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, approximately 30 miles south of Miami. The Rosensteil School of Marine and Atmospheric Sciences (RSMAS) of the University of Miami operates a research station on the island. 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

Results of an Ocean Trial of the Symbiotic Machine for Ocean uRanium Extraction

“…The uranium adsorbed during this study may also have been much less than was previously observed at BKI due to the other metal ions present in the water, specifically vanadium and copper. Vanadium exists at higher molar concentrations than uranium in seawater and has been observed to out-compete other ions, including uranium, from adsorption, though binding remains unclear. , Compared to marine deployments of the AI8 adsorbents at BKI (summarized in Table ), while the vanadium concentration did not differ considerably between the deployments, the average V:U mass ratio adsorbed by the fibers in this study was almost 2.7 times higher than observed at BKI . Figure S4 in the Supporting Information details a time series of the the mass ratio of V:U adsorbed for fibers in each enclosure on each system throughout hte 56-day deployment.…”

“…This is much lower than has been observed for other ocean tests of the AI8 adsorbent. Specifically, marine testing of the AI8 adsorbent at Broad Key Island (BKI), FL showed a maximum uranium adsorption of over 6.5 g U/kg adsorbent . Because uranium adsorption by amidoxime fibers favors warmer temperatures, − part of this difference may be due to the fact that the ambient seawater temperature at the BKI marine testing location was much warmer, ranging from 26 to 31 °C, than the ocean site in this study, which varied from 17 to 5.8 °C.…”

“…Specifically, marine testing of the AI8 adsorbent at Broad Key Island (BKI), FL showed a maximum uranium adsorption of over 6.5 g U/kg adsorbent. 31 Because uranium adsorption by amidoxime fibers favors warmer temperatures, 21−23 part of this difference may be due to the fact that the ambient seawater temperature at the BKI marine testing location was much warmer, ranging from 26 to 31 °C, than the ocean site in this study, which varied from 17 to 5.8 °C. Results from dock tests at the Woods Hole Oceanographic Institution conducted in the same manner as this experiment found the highest adsorption on AI8 fibers to be approximately 2.78 and 2.74 g U/kg adsorbent for experiments averaging 21.7 °C and 18.2 °C respectively.…”

“…20 The copper concentration during this ocean trial averaged almost twice that measured during the BKI deployment and correlated to a 5-fold difference in average Cu:U mass ratio adsorbed by the fibers. 31 These differences from previous marine deployments suggests that seawater concentrations of other ions may greatly impact uranium uptake and should be investigated further.…”

“…12,32 Compared to marine deployments of the AI8 adsorbents at BKI (summarized in Table 1), while the vanadium concentration did not differ considerably between the deployments, the average V:U mass ratio adsorbed by the fibers in this study was almost 2.7 times higher than observed at BKI. 31 Figure S4 in the Supporting Information details a time series of the the mass ratio of V:U adsorbed for fibers in each enclosure on each system throughout hte 56-day deployment. This may be due to the fact that vanadium has been found to load the adsorbent at much higher rates at colder temperatures, with vanadium saturation capacity being almost 14 times higher than the uranium saturation capacity for 8 • C and only about three times higher for 31 °C.…”