Ion exchange and fixation of rare-earth cation into expandable tetrasilicic fluorine mica

Rare-earth cation (Nd3+) are incorporated into the interlayer spaces between the silicate layers of synthetic fluorine mica, Na0.665Mg2.68(Si3.98Al0.02)O10.02F1.98, by conventional ion exchange reaction. Subsequent migration of the interlayer cations upon calcination into the vacant octahedra of 2:1 layers is followed by powder X-ray diffraction, diffuse-reflectance UV spectroscopy, and X-ray absorption spectroscopy as a function of calcination temperature. It is found from the spectroscopic analyses that the interlayer cations start to migrate into the octahedral vacant sites from 400 degreesC through the hexagonal siloxane ring of the tetrahedral silicate layers. According to the Nd L-III-edge XANES spectra, the normalized absorption intensity gradually decreases while the FWHM increases with temperature, suggesting that the bonding character of rare-earth cations and silicate lattices evolves from ionic to covalent as the calcination temperature increases.