A far infrared study of K+ ions during K+ ⇆ Ca2+ exchange in vermiculite

K+ reversible arrow Ca2+, exchange was performed on a mixed-layer (phlogopite-vermiculitc) sample from Palabora, Republic of South Africa. Exchange isotherms, X-ray diffraction patterns and far infrared (FIR) spectra of the mineral were obtained. Different mineralogical phases were identified during the exchange process: K-vermiculite, Ca-vermiculite and a regular mixed-layer (V-K-V-Ca) phase. Two types of exchange sites for K+ were identified by FIR during the exchange process. The first type, dominant in the K-vermiculite. gives an absorption band at 76 cm(-1). The other, which Was the most pronounced site in the mixed-layer phase, gives an absorption band at 72 cm(-1). The mixed-layer phase was formed only when oxidation of Fe2+ resulted in the internal compensation of part of the negative charge of vermiculite. This study shows that the high selectivity displayed by vermiculite for K+ is enhanced by the formation of the mixed-layer phase.