Polyethylene fibers functionalized with amidoxime ligand have been conditioned with various base solutions at different temperatures, time periods, and ratios of base-solution volume to adsorbent mass. Infrared spectroscopy has been employed to provide a better understanding of the chemical interaction of the base with the amidoxime ligand. Results have shown that, as the conditioning period increases, the intensity of the C=N and N-O peaks decreases, while the intensity of the C=O peak increases. An optimal ratio of the C=N and/or N-O peak to the C=O peak seems to play a vital role in enhancing the uranium adsorption performance of the adsorbent. Testing of the adsorbent has been performed with 1-L synthetic solution and 5-gallon natural seawater. Kinetic data and mechanistic modeling were employed to determine the rate-limiting mechanism of the uranium uptake process. Four mechanisms were examined for investigation of the rate-limiting mechanism of the uranium uptake process: interparticle diffusion, external film mass transfer, intraparticle diffusion, and complexation reaction. It was revealed that the rate-limiting mechanism of the process is the complexation reaction between the amidoxime ligand and the uranyl ion in seawater. The hypothesis is that this reaction is slow in the presence of bicarbonate ions in seawater, which form uranyl tricarbonate. This species is stable, so that the amidoxime ligand competes with bicarbonate ions in reacting with uranyl ions, and this competition slows down the uranium uptake rate by the adsorbent. Controlled kinetic experiments with simulated uranium solutions have demonstrated the effect of bicarbonate and sodium ions on the uranium uptake process. One-liter batch experiments with synthetic uranium solution were also performed to investigate the effects of additional parameters including (i) presence of competitive ions in the solution such as those of vanadium, calcium, and magnesium and (ii) adsorbents having different uranium loading capacities. Modeling results are in good agreement with experimental data obtained from both 1-L synthetic uranium solutions and natural seawater.<br/>This research was sponsored by the US Department of Energy, Office of Nuclear Energy under contract DE-AC05-00OR22725 with Oak Ridge National Laboratory, managed by UT-Battelle, LLC.

Adsorbent pretreatment and batch kinetic experiments for uranium adsorption testing and modeling

249th National Meeting (2015)

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