Volume changes associated with zeolite ionic exchange

Abstract

Aqueous suspensions of zeolite(4A) in the potassium and sodium forms have been separately exchanged with Ca²⁺ at 25ºC in a precision dilatometer to measure the associated system volume change, ∆V_obs. Similar experiments partially exchanged K⁺ into sodium zeolite(4A) and Na⁺ into potassium zeolite(4A). Tris(ethane-1,2-diamine)cobalt(III) chloride was also exchanged with sodium zeolite(13X). For the overall process ∆V_obs is small, generally well under 10 cm³ per mole of incoming cation exchanged.

The results are discussed in terms of three contributions to the overall volume change: (i) the volume change of ionic replacement in the solution external to the zeolite (this is available from the known apparent molar volumes of the electrolytes); (ii) the small dimension changes of the zeolite lattices on exchange; (iii) the transfer of water between zeolite and the solution phase.