LOCAL-STRUCTURE OF THE INTERLAYER ION IN SYNTHETIC FLUORINE MICA

Na-form tetrasilicic fluorine micas, i.e., sodium taeniolite (NaT, NaM g2LiSi4O10F2.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 select ivity for K+, Rb+, and Cs+ and NaH does for Rb+ and Cs+. XAFS of the e xchanged ions in NaT and NaH were analyzed and powder X-ray diffractio ns were measured to investigate the layer stacking. Characteristics of ion-exchange selectivity of these micas were revealed by the local st ructure of the interlayer ion. Rb K-edge EXAFS of all samples show sli ghtly longer Rb-O-1st distance than K-O-1st in taeniolite (its origina l anhydrous K-form). It indicates that Rb+ for the micas is exchanged as an anhydrous state. X-Ray diffraction patterns showed hydrated inte rlayer-ion phases at low-exchanged NaT and NaH. The hydrated phases de creased with increasing the exchange ratio and then less-hydrous Ph-ph ase increased. Although Cs+-exchanged NaT show only an anhydrous state in XAFS, Sr2+ and Ba2+ in NaT was hydrous as if in aqueous solution.