Characterization of uranium uptake kinetics from seawater in batch and flow-through experiments

A laboratory study of uranium uptake from seawater has been conducted using batch and flow-through recycling experiments. Uranium adsorption from seawater, using amidoxime-based polymeric adsorbents, has been described by transport and kinetic models under the assumption of transport-limited or reaction-limited process for batch adsorption experiments. Mathematical models based on liquid film mass transfer, diffusion, or reaction kinetics have been evaluated in terms of the Sherwood number and the Thiele modulus to provide insight into the limiting mechanism. The value of the Sherwood number suggests that the external mass-transfer resistance is much smaller than the intraparticle diffusion resistance. The Thiele modulus was estimated on the basis of the rate constants from independent batch tests analyzed by a reaction kinetic model, and its value suggests that the uranium binding is the rate-limiting step compared to diffusion. The uranium uptake in batch experiments reached 4 mg U/g adsorbent over a period of nine weeks, which is much higher than the uranium uptake by a leading previously developed adsorbent tested at conditions similar to those in this study. The maximum uranium uptake in the flow-through recycling experiments was approximately 3.3 mg U/g adsorbent over a period of six weeks.