Intraparticle mass transfer in bidispersed porous ion exchanger part I: Isotopic ion exchange

A simple theoretical equation of intraparticle effective diffusivity 𝒟e, in a bidispersed porous ion exchanger was derived under the assumption of parallel diffusion in the solid phase and the macropore. 𝒟e of Na+, CO2+, Zn2+ and Ce3+ in several MR‐type resins and other type of porous resins (P‐type resin) were measured by isotopic ion exchange. In MR‐type resin, 𝒟g was affected by the concentration of the bulk solution Co and was separated into a solid phase diffusivity 𝒟g and a macropore diffusivity 𝒟p by using the derived equation. Equations for estimating 𝒟g were obtained. The diffusivity ratio of 𝒟p to diffusivity in infinitely dilute aqueous solution for a monovalent ion agreed with the Neale and Neder's theoretical equation for tortuosity factor within 10%. In P‐type resin, it became clear that the effect of macropore diffusion is negligible. 𝒟e was little affected by Co. Separated 𝒟p was little larger than 𝒟g, and 𝒟g was nearly equal to 𝒟e. The equations for estimating 𝒟g of a P‐type resin were quite similar to those for gel‐type resins.