Maxwell-Stefan based modelling of ion exchange systems containing common species (Cd²⁺, Na⁺) and distinct sorbents (ETS-4, ETS-10)

Cadmium(II) is a toxic hazardous cation, whose presence in the environment causes great concern because of its bioaccumulation in organisms and bio amplification along food chain. Hence, the removal of cadmium compounds from industrial waters and wastewaters is particularly essential, which requires intensive experimental and modelling studies to deal with the problem. In this work, the ion exchange of Cd²⁺ ions from aqueous solution using microporous titanosilicates (ETS-4 and ETS-10) has been modelled using adapted Maxwell-Stefan equations for the ions transport inside the sorbent particles. The fundamentals of the Maxwell-Stefan equations along with correlations for the convective mass transfer coefficients have been used with advantage to reduce the number of model parameters. In the whole, the model was able to represent successfully the kinetic behaviour of 11 independent and very distinct curves of both studied systems (Cd2^+/Na⁺/ETS-4 and Cd²⁺/Na⁺/ ETS-10). The predictive capability of the model has been also shown, since several uptake curves were accurately predicted with parameters fitted previously to different sets of experimental data.