Abstract
High-surface-area amidoxime and carboxylic acid grafted polymer adsorbents developed
at Oak Ridge National Laboratory were tested for sequestering uranium in a flowing seawater
flume system at the PNNL-Marine Sciences Laboratory. FTIR spectra indicate that a KOH
conditioning process is necessary to remove the proton from the carboxylic acid and make the
sorbent effective for sequestering uranium from seawater. The alkaline conditioning process also
converts the amidoxime groups to carboxylate groups in the adsorbent. Both Na2CO3H2O2 and
hydrochloric acid elution methods can remove ~95% of the uranium sequestered by the adsorbent
after 42 days of exposure in real seawater. The Na2CO3H2O2 elution method is more selective
for uranium than conventional acid elution. Iron and vanadium are the two major transition metals
competing with uranium for adsorption to the amidoxime-based adsorbents in real seawater. Tiron
(4,5-Dihydroxy-1,3-benzenedisulfonic acid disodium salt, 1 M) can remove iron from the adsorbent very effectively at pH around 7. The coordination between vanadium (V) and
amidoxime is also discussed based on our 51V NMR data.
