Peculiarities of the Dynamics of Ion Exchange in Supersaturated Solutions and Colloid Systems

This paper reports the results obtained by experimental and theoretical study of the dynamics of ion exchange accompanied by the ion-exchange isothermal supersaturation (IXISS) effect. This effect is observed for a number of ion-exchange systems where the frontal or the reverse frontal separation is accompanied by the formation of extremely stable supersaturated solutions of low solubility substances in the interstitial space of ion-exchange columns. After leaving the column, a supersaturated solution crystallizes spontaneously, which allows for designing a practically ideal ion-exchange process where a crystalline product is obtained directly after the ion-exchange treatment cycle. The paper comprises results on the experimental investigation of IXISS of magnesium carbonate on carboxylic resins, which is observed in desorption of Mg 2+ from the resin in the Mg form with Na 2 CO 3 solutions or with solutions of Na 2 CO 3 −NaHCO 3 mixtures. The physical and mathematical models of the kinetics and the dynamics of the ion-exchange processes proceeding in a colloid system comprising a supersaturated solution and an ion exchanger, which surface is partially blocked by adsorbed precrystalline aggregated (micelles), are proposed, and their validity is experimentally confirmed.