Modeling chromate ion-exchange processes



In spite of chromate's very high selectivity at acidic pH, fixed-bed chromate-exchange processes always suffer from severe gradual breakthroughs of chromate during column runs. Earlier, Sengupta and Clifford confirmed that such a gradual breakthrough is an equilibrium phenomenon and provided the underlying ion-exchange mechanism. An algorithm, developed with the aid of the governing chromate ion-exchange mechanism, is presented here to predict the salient properties of chromate-exchange processes in a multicomponent system. The model predicts the gradual chromate breakthroughs during column runs fairly accurately and also accounts for other unusual characteristics of chromate ion exchange. Average separation factor models, often used for designing fixed-bed ion-exchange processes, are unable to predict the gradual breakthrough characteristics of a preferred component such as chromate.