An activity model for multi-component ion exchange

Ion exchange resin is used extensively in the mineral processing industry to recover dissolved species form solution. These processes are usually modeled using a dual resistance model incorporating both external film diffusion and some form of intraparticle diffusivity. Although this type of model is tested and proven in many systems, certain assumptions relating to the model makes it impractical to apply to certain ion exchange operations, especially those involving multi-component ion exchange. This study addresses these short-comings by using a dual kinetic rate model which does not rely on accurately predicting equilibrium conditions. The model assumes that ion exchange takes place from a liquid layer surrounding the particle and that a single rate constant can be used to explain ion exchange kinetics from this ‘proximity’ layer. Furthermore, the concentration of a species in the bulk solution is influenced by the rate at which it is transported into the ‘proximity’ liquid layer. The model has been applied to various systems and proved to be extremely effective. Also, the model was able to describe reversible ion exchange.