Resin-phase diffusivity in isotopic ion exchange was measured by the single-particle method.
The effect of resin diameter, the degree of crosslinking and the concentration and valence of ionic species on resin-phase diffusivity were studied with a macroscopic model by which the diffusivity may be predicted. From these results, the estimating equation of resin-phase diffusivity for sulfonated styrene type resin in the range of the degree of crosslinking 3-16% was obtained.