Calcium and fluoride release from ion exchange polyphasic systems

The present study concerns the kinetics of ion exchange accompanied by CaF2 precipitation in tri-phasic and quadri-phasic systems involving a weak base anionic exchanger and a carboxylic cationic exchanger in the F- and Ca2+ forms, respectively, in contact with a solution of artificial saliva. It was shown that in both systems the rate of Ca2+ release from the cationic exchanger is much lower than that of F- from the anionic one. The rate of release for both ions, controlled by intraparticle diffusion, has been characterized by a Pick's law model. The kinetic parameters of effective rate of release (B) and diffusion coefficient (D) of the respective ion in the resin phase depend on the type of resin and the presence of different numbers of phases. The amount of the precipitate crystallizing on the surface of the resin beads depends on the type of the ion exchange resin, its particle size and on the ratio of resin components. By varying this ratio and the particle size of the ion exchangers it is possible to accomplish the precipitation mostly on the larger surface of the ionic exchanger. © 2003 Society of Chemical Industry.