Equilibrium behaviour of exchange of [Coen3]3+ on vermiculite

Summary The cation exchange data of tris ethylene diamine cobaltic ion on H-vermiculite fit in with theLangmuir equation. The exchange of [Coen₃]³⁺ by different cations are in the order: Li < Na < NH₄ < K < Rb < H < Cs for the monovalent, Mg Ca < Ba for the bivalent and (C₂H₅)₄N < (CH₃)₄N CTA < CP for monovalent organic ions. Quaternary cations such as (C₂H₅)₄N⁺ exchange less than (CH₃)₄N⁺. This may be ascribed to the larger size of the former and also to the limitedc-axis expansion of vermiculite. By use of the equation ofKielland, thermodynamic equilibrium constants and standardGibbs free energy change have been evaluated. The plots of log (selectivity coefficient) vs. hydrated ionic radius and the reciprocal of theDebye Hückel parametera⁰, suggest that the parametera⁰ rather than the hydrated ionic radius may be found to correlate with the relative affinities of univalent cations for the vermiculite surface.