Cation migration

The AS-values increased with respect to those of the dehydrated samples (8), especially for the samples with high H20/cation ratios. This means that there is a distortion of the cationic hydration shell or a partial dehydration of the cations during migration (18). In other words, water around the migrating cations cannot be regarded water of hydration. In that respect, hydrated zeolites resemble concentrated cationic solutions (19). 

Standard cell sizes are up to 30 by 45 in. In an individual stack the compartments are in parallel, but several stacks in series are employed to achieve a high degree of ion exchange. The ion exchange membrane is not depleted and does not need regeneration. The mechanism is that an entering cation under the influence of an emf replaces an H+ ion from the resin and H+ from solution on the opposite face of membrane replaces the migrating cation. 

As shown in Eqs. (3.9) and (3.10), the concentration of migrating cations is a squared function of the adsorbate concentration in the outer volume of the solution. The Donnan distribution is a source of serious error when determining M of ionic polysaccharides by membrane osmometry. Polyanions may be freed of cations and excess HsO+ by electrodialysis. 

Na" " and Nd with increasing temperature, and that the ion-exchanged Nd -P"-alumina was not a pure trivalent Nd cationic conductor, but rather a Na and Nd mixed ionic conductor at elevated temperatures. The existence of other ion-exchanged Ln -P"-aluminas has also been in doubt, notably with regards to whether Ln is the only migrating cationic species, or not, and for the same reason as considered for Nd -P"-alumina. 

Garcia-Vergara S.J., Skeldon R, Thompson G.E. and Habazaki H. (2008), Behaviour of a fast migrating cation species in porous anodic alumina , Cotros. Set, 50, 3179-84. 

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