The isotopic exchange kinetics of Zn2+ ions in hydrated Zn-A zeolite of composition Zn5·55Na0·90(AlO2)12(SiO2)12·aq were investigated by measuring the fractional attainment of isotopic equilibrium between a ZnCl2 solution and a 65Zn-labelled Zn-A zeolite (30 and 45μm particle radii) as a function of time, at 25 to 60C. The exchange mechanism was a two-step process which was resolved, using the Brown-Sherry-Krambeck model, into diffusion in the solid particles, with a Zn2+ diffusivity described by:

D(m2/s) = 10-3.97exp[-67.1(kJ/mol)/RT]

and an intracrystalline first-order exchange between bound and mobile Zn2+ ions in the network, with a rate constant given by k2(/s) = 103.05exp[-

56.5(kJ/mol)/RT].

V.M.Radak, I.J.Gal, J.J.Salai: Journal of the Chemical Society - Faraday Transactions 1, 1976, 72, 1150-6