A simplified resistance model for reversible multicomponent ion exchange

Ion exchange resins have found increasing application in the metallurgical sector over the last few decades through resin-in-column (RIC) technology. These processes are usually simulated by using some form of resistance model. Furthermore, of these, a dual resistance approach incorporating both film and pore-wall diffusion is the most popular and widely used technique for simulations involving ion exchange and adsorption processes. This procedure assumes that equilibrium exists at the solid/liquid interface, an assumption easily applied to single-component systems. However, in multicomponent systems, this assumption makes the simulation procedure cumbersome. In addition, the inability of frequently used isotherms to accurately describe equilibrium conditions over a wide range of solution concentrations results in significant errors. This study investigates the use of a simple film-diffusion mechanism to describe mass transfer kinetics. Furthermore, a simplified Fritz and Schleunder isotherm was used to overcome complex iterative techniques in order to obtain equilibrium conditions at the solid/liquid interface. The procedure was evaluated using a chelating resin in a ternary system and proved to be very effective with reversibility well explained. Moreover, it has been shown that the effect of the counter-ion may be ignored in batch operations but not in column configurations because of the significant increase of the counter-ion in solution.