The cation-exchange kinetics and thermodynamic equilibria for alkaline-earth metals by Na-3-mica [chemical composition of Na2.94(Mg5.55Ti0.07Fe0.04)oct(Al2.07Si5.83)tetO20F4·1.72H2O] with a high layer charge were investigated at room temperature. The Ba, Sr, Ca and Mg uptake kinetics were determined and first-order, modified Freundlich, parabolic diffusion and Elovich kinetic models were examined for the experimental data. The first-order model gave a relatively good fit throughout for these cations and indicated a kinetic selectivity order of Ca2+ < Mg2+ < Sr2+ < Ba2+. The cation exchange isotherms for Ba, Sr, Ca and Mg uptakes with the Na-3-mica were also determined. The Kielland plots evaluated from the cation exchange isotherms showed a thermodynamic selectivity order of Ba2+> Sr2+> Ca2+ > Mg2+. The above basic studies on the selective cation exchange of the highly charged ion exchanger are of relevance in the separation, immobilization and disposal of 90Sr from aqueous nuclear wastes.
All Science Journal Classification (ASJC) codes
- Materials Chemistry