Far infrared study of K+, Rb+ and Cs+ during their exchange with Na+ and Ca2+ in vermiculite

All the exchange isotherms of Na + or Ca 2+ in vermiculite for K + , Rb + or Cs + show two kinds of exchanges sites: the first corresponds to sites located in phlogopite-like interlamellar spaces and the second to sites located in smectite-like interlamellar spaces. During the exchange, three mineralogical phases are formed: Na- or Ca-vermiculite; K-, Rb- or Cs-vermiculite and a mixed-layer phase. Far infrared absorption bands of K + , Rb + and Cs + located in the phlogopite-like interlamellar spaces are at 72, 59 and 53 cm -1 , respectively. These frequencies are characteristic of a trioctahedral mixed-layer phase. Selectivity is greater for cations with a low hydration energy (K + , Rb + , Cs + ) than for cations with a high hydration energy (Na + , Ca 2+ ). On the other hand, for cations with a low hydration energy, structural parameters such as the tetrahedral rotation angle, α, have to be taken into account.