Thermodynamic study of alkali and alkaline-earth cation-exchanged natrolites

A series of synthetic natrolites with different non-framework cations (Li-NAT, Na-NAT, K-NAT, Rb-NAT, Cs-NAT, Ca-NAT, Sr-NAT and Pb-NAT) are investigated by high temperature oxide melt solution calorimetry. The formation enthalpy from the component oxides (Delta H-f,H-ox) becomes less exothermic with increasing ionic potential (Z/r) of the cations. The dehydration behavior of NATs is examined using TG-IDSC. The strength of water binding decreases with increasing cation size. Similar to the trend seen in anhydrous zeolites, a linear dependence of Delta H-f,H-ox on Al/(Al + Si) ratio for hydrous zeolites is established. (C) 2012 Elsevier Inc. All rights reserved.