Transition metal ion exchange in zeolites. Part 2.—Ammines of Co3+, Cu2+ and Zn2+ in clinoptilolite, mordenite and phillipsite

Abstract

Exchange of cuprammine and zincammine ions in ammonium forms of clinoptilolite, mordenite and phillipsite has been studied in ammoniacal solution, pH > 10, and similar investigations are reported on the [Co(NH₃)₆]³⁺ ion at pH values of ∼5 and ∼10 in mordenite. Isotherms were too rectangular to calculate values of the standard free energy of exchange, and selectivities were very much higher than for the corresponding aquo ions in mordenite at low pH. Analyses of the zeolites revealed that the intracrystalline Cu²⁺ and Zn²⁺ ions had ∼three NH₃ ligands and that the cobaltic ion retained six NH₃ molecules. The increase in selectivities observed with mordenite when the cobalt, copper and zinc ions were complexed with ammonia has been rationalised in terms of dielectric theory.