Processing of Plutonium by Ion Exchange-VI. Plutonium (IV) Sorption Kinetics on Dowex 1×4 from Nitrate Solutions

The kinetics of the sorption of plutonium (IV) on Dowex 1 × 4 from nitrate solutions are presented. Sorption rates from various nitric acid and mixed aluminum-nitrate/nitric-acid solvents were studied. The particle-diffusion controlled reaction proceeds with an apparent average diffusion coefficient which decreases exponentially with increasing plutonium sorption. The results agree reasonably well with a computer solution of Fick's law with the local intraparticle diffusion coefficient proportional to the local intraparticle fraction of unreacted exchange sites. The trace-sorption diffusion coefficient is strongly dependent upon the composition of the aqueous phase, and is empirically shown to be roughly inversely proportional to the product of the trace-sorption distribution coefficient and the ratio of the hydronium ion-to-water concentrations. These kinetic results and previously reported equilibrium parameters may be coupled with the fundamental partial-differential equation which describes the operation of a fixed-bed anion-exchange column to allow computer optimization of plant-scale processing equipment. The effects of the variation of such parameters as volume and mass flow rate, temperature, plutonium feed concentration, and macro concentrations of aluminum nitrate in the feed are qualitatively discussed for one equipment design.