Self-diffusion of Fe(III) in ion-exchanger dowex 50W-X8

Abstract

The isotopic exchange of ferric ion within Dowex 50W-X8 has been studied. The self-diffusion coefficients were calculated with Fick's law model, and found to increase from 3·46 to 10·45 × 10 −8 cm 2 sec −1 as the temperature is raised from 15° to 55°C. The activation energy is slightly reduced from 5·8 to 3·7 kcal/mole in the above temperature range. When the particle size of the resin is changed from 18 to 40 mesh, a linear plot is obtained for contact time vs. diameter of particle at a definite F( t) The organic solvent effect on the diffusion of cations in resin is also discussed with aid of Gainer and Metzner's equation of binary diffusion, and a conclusion is drawn that the self-diffusion of cation in resin is actually a binary diffusion; i.e., a solute diffusing through the medium of a solvent. Only when the temperature is high, the diffusion of cations is independent of the solvent flow. The distance between two successive equilibrium positions, λ, can be calculated by using Gainer's equation and Houghton's formula. In this research, λ is found to be 0·87 Å. This small value of λ indicates the concentratedness in the resineous phase, and thus explains the slowness of the self-diffusion of cations in the resin particles.