Cation‐exchange Equilibria With Vermiculite

Summary The exchange of Na, Mg, Ca, Sr, and Ba ions has been studied in the temperature range 25° C‐70° C. Vermiculite shows a preference for divalent ions over Na ions at 25° C and the preference increases very greatly at higher temperatures. The preference is largely determined by the increase in entropy which accompanies the replacement of monovalent ions by divalent ions in the vermiculite. Preference is less marked between divalent ions. These ions are similarly hydrated in vermiculite, which differs in this respect from resins and most other clay minerals. The greater affinity of Mg ions compared with other divalent ions is explained by their closer approach to the silicate surfaces.