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

Abstract

Abstract K + ⇋ Ca 2+ exchange was performed on a mixed-layer (phlogopite-vermiculite) 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 Fe 2+ 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.