Marine testing of adsorbent fibers is being conducted in packed columns using flow-through filtered natural seawater in which temperature and flow-rate are controlled at realistic marine conditions.  Measurements of the adsorption of uranium and other elements from seawater as a function of time onto the adsorbent materials are used to determine the adsorbent capacity and adsorption rate (kinetics) of uranium and other elements.  The Oak Ridge National Laboratory (ORNL) amidoxime-based adsorbent, 38H, developed in 2012, had an adsorption capacity of 3.26 ± 0.70 mg U/g adsorbent after 56 days of exposure at 20 °C (normalized to a salinity of 35 psu).  Applying a one-site ligand saturation model predicts a saturation adsorption capacity of 4.89 ± 0.80 mg U/g of adsorbent material (normalized to a salinity of 35 psu) and a half-saturation time of 28 ± 10 days.  A newer amidoxime-based adsorbent developed by ORNL,   AF1, had a 56 day adsorption capacity of 3.85 ± 0.20 mg U/g adsorbent, a saturation adsorption capacity of 5.3 ± 0.2 mg U/g adsorbent, and a half-saturation time of 21 ± 2 days.  Marine testing of braided adsorbents is being conducted in temperature and flow-rate controlled flumes. The AF1 adsorbent had a slightly higher 56 day adsorption capacity (4.1 ± 0.2 mg U/ g adsorbent), a slightly higher saturation capacity (6.4 ± 0.2 mg U/ g adsorbent), and a slightly longer half-saturation time (32 ± 2 days) in the flume studies. Time series experiments were conducted with three separate formulations of the ORNL amidoxime-based polymeric adsorbent (38H, AF1 and AI8) to assess the impact of adsorption capacity due to temperature. For all three adsorbents, a strong, fairly linear, relationship was observed between temperature and adsorption capacity; as the temperature increased, so did the adsorption capacity.  However, the three adsorbents showed different temperature responses.   For the ORNL 38H, AF1 and AI8 adsorbents, the adsorbent capacity increased 40, 180, and 237 µg U/ g adsorbent/1°C, respectively.  The amidoxime-based adsorbent materials are not element specific. The majority of the binding sites are occupied by the major cations in seawater (Mg, Ca, and Na).  For the trace elements, the order of importance for a suite of trace elements (in units of mol/g) observed for the AF1 adsorbent was V, Fe, Zn, K, U, Cu, Ni, Sr, Ti, Cr, Co, Mn and Mo.

Characterization and testing of adsorbent materials to extract uranium from natural seawater

249th National Meeting (2015)

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