Abstract
Extraction of uranium (U) from seawater for use as a nuclear fuel is a significant
challenge due to the low concentration of U in seawater (~3.3 ppb) and difficulties to
selectively extract U from the background of major and trace elements in seawater. The
Pacific Northwest National Laboratory (PNNL)’s Marine Sciences Laboratory (MSL) has
been serving as a marine test site for determining performance characteristics (adsorption
capacity, adsorption kinetics, and selectivity) of novel amidoxime-based polymeric
adsorbents developed at Oak Ridge National Laboratory (ORNL) under natural seawater
exposure conditions. This report describes the performance of three formulations (38H,
AF1, AI8) of amidoxime-based polymeric adsorbent produced at ORNL in MSL’s
ambient seawater testing facility. The adsorbents were produced in two forms, fibrous
material (40-100 mg samples) and braided material (5-10 g samples), exposed to natural
seawater using flow-through columns and recirculating flumes. All three formulations
demonstrated high 56 day uranium adsorption capacity (>3 gU/kg adsorbent). The AF1
formulation had the best uranium adsorption performance, with 56-day capacity of 3.9 g
U/kg adsorbent, saturation capacity of 5.4 g U/kg adsorbent, and ~25 days half-saturation
time. The two exposure methods, flow-through columns and flumes were demonstrated
to produce similar performance results, providing confidence that the test methods were
reliable, that scaling up from 10’s of mg quantities of exposure in flow-through columns
to gram quantities in flumes produced similar results, and that the manufacturing process
produces a homogenous adsorbent. Adsorption kinetics appear to be element specific,
with half-saturation times ranging from minutes for the major cations in seawater to 8-10weeks for V and Fe. Reducing the exposure time provides a potential pathway to
improve the adsorption capacity of U by reducing the V/U ratio on the adsorbent.
