Abstract
As a precursor to some detailed studies on the selectivity of the minerals clinoptilolite, ferrierite and mordenite for lead and cadmium, the equilibrium properties of the ammonium/sodium exchange have been studied in all three zeolites. With no zeolite was full replacement of sodium by ammonium ion observed, a result which conflicts with earlier work on clinoptilolite. In natural mordenite, only 50% of the sodium ions were replaced by ammonium; this shows a significant difference in properties between natural and synthetic mordenite. In ferrierite, the exchange was found to be ternary in nature, involving sodium, ammonium and potassium. Substantial quantities of calcium were found in solution after equilibrations of sodium/ammonium with either natural clinoptilolite or mordenite. This calcium arose however primarily through dissolution of calcite, and the exchange in these cases appeared to be primarily binary in nature.
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