Ion exchange selectivity of phillipsite for Cs and Sr as a function of framework composition

Cs and Sr exchange reactions for Na on sedimentary, hydrothermal and synthetic phillipsites are studied by determining their exchange isotherms at 25 degrees C and 0.1 total normality, and computing the related thermodynamic quantities K-a, and Delta G degrees. Sedimentary and synthetic phillipsite, characterized by a higher Si/Al ratio, display good selectivity for Cs and moderate selectivity for Sr. The more aluminous hydrothermal phillipsite displays a lower selectivity for Cs and a higher selectivity for Sr than sedimentary and synthetic phillipsite do. These results, perfectly explainable in terms of field strength of the anionic zeolite framework and of ion charge density, demonstrate that the joint removal of Cs and Sr from water by phillipsite would be possible, provided cheap widespread aluminous phillipsite-rich materials were available.