Natural zeolites and their ion exchange behavior towards chromium

Zeolitic material synthesised from fly ash: use as cationic exchanger

“…This phenomenon has been previously described by other authors. 17 On the other hand, the zeolite saturation process and pH trends are similar to those for the ion exchange resin, but in the latter case exchange is completed in a shorter period of time (Fig 4). It could be said that in spite of the higher valence of this cation its access to the channels is not dif®cult because it has the smallest size, therefore the retention capacities are similar to the other cations.…”

The removal of heavy metal cations by natural zeolites

“…The chemical composition, the theoretical exchange capacity, and the Si/Al ratio, generally ranging from 4 to 5.5, are typical for clinoptilolite [28][29][30]. Low-silica members are enriched with calcium, whereas high-silica clinoptilolites are enriched with potassium, sodium, and magnesium.…”

Ion exchange studies on natural and modified zeolites and the concept of exchange site accessibility

“…Diffusion coefficients for Pb 2+ and Cd 2+ in Na-rich and natural clinoptilolite have been measured [3,[14][15][16] and for Cu 2+ on Na-and Ca-rich clinoptilolite [17]. Kinetics of Pb 2+ and Cu 2+ in Narich clinoptilolite has been reported [13], for Pb 2+ and Cd 2+ on natural and Na-rich clinoptilolite [18,19], for Cr 3+ ions [20], and for Pb 2+ and Cu 2+ , but without determination of diffusion coefficients [11].…”