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The Pacific Northwest National Laboratory (PNNL) is evaluating the performance of adsorption materials to extract uranium from natural seawater. Testing consists of measurements of the adsorption of uranium and other elements from seawater as a function of time using flow-through columns and a recirculating flume to determine adsorbent capacity and adsorption kinetics. The amidoxime-based polymer adsorbent AF1, produced by Oak Ridge National Laboratory (ORNL), had a 56-day adsorption capacity of 3.9 ± 0.2 g U/kg adsorbent material, a saturation capacity of 5.4 ± 0.2 g U/kg adsorbent material, and a half-saturation time of 23 ± 2 days. The ORNL AF1 adsorbent has a very high affinity for uranium, as evidenced by a 56-day distribution coefficient between adsorbent and solution of log KD,56day = 6.08. Calcium and magnesium account for a majority of the cations adsorbed by the ORNL amidoxime-based adsorbents (61% by mass and 74% by molar percent), uranium is the fourth most abundant element adsorbed by mass an...

A variety of adsorbent materials have been developed to extract uranium from seawater as an alternative traditional terrestrial mining. A large-scale deployment of these adsorbents would be necessary to recover useful quantities of uranium, and this raises a number of concerns regarding potential impacts on the surrounding marine environment. Two concerns are whether or not the adsorbent materials are toxic and any potentially harmful effects that may result from depleting uranium or vanadium (also highly concentrated by the adsorbents) from the local environment. To test the potential toxicity of the adsorbent with or without bound metals, Microtox assays were used to test both direct contact toxicity and the toxicity of any leachate in the seawater. The Microtox assay was chosen because it detected nonspecific mechanisms of toxicity. Toxicity was not observed with leachates from any of the 68 adsorbent materials that were tested, but direct contact with some adsorbents at very high adsorbent concentrati...

The Marine Science Laboratory at the Pacific Northwest National Laboratory evaluated the impact of biofouling on the performance or uranium adsorbents. A surface-modified polyethylene adsorbent fiber provided by Oak Ridge National Laboratory, AF adsorbent, was tested in either the presence or absence of light to simulate deployment in shallow or deep marine environments. Samples of the adsorbent fiber were exposed to seawater as loose fibers packed with glass beads in columns and as >10-cm-long braids of fiber placed in a flume that provided a continuous flow representative of natural ocean currents. Exposure tests (42 days) in column and flume settings showed that biofouling resulted in decreased uranium uptake by the adsorbent fiber. Uranium uptake was reduced by up to 30%, in the presence of simulated sunlight, which also increased biomass accumulation and altered the microbial community composition on the fibers. These results suggest that deployment below the photic zone would mitigate the effects of...