Na-form tetrasilicic fluorine micas, i.e., sodium taeniolite (NaT, NaMg2LiSi4O10F2.nH2O) and sodium hectorite (NaH, Na1/3Mg8/3Li1/3Si4O10F2.nH2O), exchanges their Na+, the interlayer cation, for K+, Rb+, Ca2+, Ni2+, and other cations in solutions. NaT shows remarkably high selectivity for K+, Rb+, and Cs+ and NaH does for Rb+ and Cs+. XAFS of the exchanged ions in NaT and NaH were analyzed and powder X-ray diffractions were measured to investigate the layer stacking. Characteristics of ion-exchange selectivity of these micas were revealed by the local structure of the interlayer ion. Rb K-edge EXAFS of all samples show slightly longer Rb-O1st distance than K-O1st in taeniolite (its original anhydrous K-form). It indicates that Rb+ for the micas is exchanged as an anhydrous state. X-Ray diffraction patterns showed hydrated interlayer-ion phases at low-exchanged NaT and NaH. The hydrated phases decreased with increasing the exchange ratio and then less-hydrous Rb-phase increased. Although Cs+-exchanged NaT show only an anhydrous state in XAFS, Sr2+ and Ba2+ in NaT was hydrous as if in aqueous solution.
Journal de Physique IV, 7 (Colloque 2) C2-1165 - 1166 (1997).
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