IMPLICATIONS OF WEAK DONNAN POTENTIAL IN ION-EXCHANGE REACTIONS - AN ALTERNATE STRATEGY FOR MODELING SORPTION PROCESSES

Donnan potential generated during an ion-exchange process is conventio nally believed to play an important role in partitioning co-ions in th e resin and solution phases; most earlier studies implied near total e xclusion of co-ions from the resin pores. The present work attempts to investigate implications of weak Donnan potential with specific refer ence to the sorption of acids on weak base resins. An alternate mathem atical treatment has been proposed to describe the sorption behavior o f any type of acid by assuming diffusion and sorption of single specie s, the composite acid molecule, in the resin pores. Fick's law is then used to characterize the diffusion process. The proposed model is val idated using data reported in the literature for the sorption of a str ong monobasic acid (HCl) and also for a weak monobasic acid (HCOOH). T he fit of the model is excellent, and the regressed values of the effe ctive diffusion coefficient are shown to be reasonable and correct to the order of magnitude. The model is expected to offer a simpler and u nified approach for modeling sorption behavior of different types of a cids and will be more useful in problems of acid separation from mixtu res.