Transition metal ion exchange in zeolites. Part 1.—Thermodynamics of exchange of hydrated Mn2+, Co2+, Ni2+, Cu2+ and Zn2+ ions in ammonium mordenite

Authors:
  • RBRichard M. Barrer
    Richard M. Barrer
  • RTRodney P. Townsend
    Rodney P. Townsend
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Abstract
Ion exchange of Mn2+, Co2+, Ni2+, Cu2+ and Zn2+ in ammonium mordenite has been studied in aqueous solution over a pH range of 4–7 at 25°C. Values of the thermodynamic equilibrium constant Ka and the standard free energy of exchange ΔG⊖ were calculated for reversible systems. In no case at 25°C did the degree of exchange of metal ions exceed 50%, and pH and anion were found to have no significant effect on the equilibria. A thermodynamic affinity sequence of Mn2+ > Cu2+ > Co2+∼ Zn2+ > Ni2+ was established and thermodynamic affinities of the zeolite for pairs of metal ions were calculated using the triangle rule. Selectivity quotients indicated that mordenite would preferentially remove manganese(II) or copper(II) from a binary solution mixture of one of these ions with cobalt(II), nickel(II) or zinc(II).