Interdiffusion of A and B in Zeolite Crystals as the Limiting Step

If the electrolytic solution has a very high volume and, consequently, the concentration of the cation A is practically constant throughout the ion-exchange process, the experimental setup exhibits the following initial and boundary conditions [44]  

For the calculation of the effective diffusion coefficient, De, a procedure where the series in Equation 7.27 is truncated can be applied, and taking the first four terms, that is, 

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