NH4 exchange in chabazite, heulandite–clinoptilolite, and phillipsite

Abstract

In order to evaluate the NH4 exchange capacity of the chabazite, heulandite–clinoptilolite, and phillipsite zeolite species, crystals of “amygdaloidal” occurrence with different chemical compositions were treated in batch (static method) and in column (dynamic method) with 1 N NH4Cl solution in varying experimental conditions (temperature, grain size). The degree of exchange was expressed as the percentage of each exchanged cation (Ca, Na, and K) with respect to the theoretical value calculated from the original chemical composition. The total percentage of the exchanged cations was also reported. The 70 °C static treatments evidenced that the exchange was especially high in chabazite. At the same temperature the exchange increased in heulandite–clinoptilolite at decreasing grain size. With respect to the 70 °C treatments, the room temperature static treatments showed a lowered exchange in phillipsite and heulandite–clinoptilolite, and subordinately in chabazite. In the dynamic treatments, the exchange was significantly higher in chabazite than in phillipsite and heulandite–clinoptilolite, and increased at decreasing grain size. On the whole, chabazite revealed the highest degree of exchange. The exchange capacity was slightly influenced by the Si/(Si + Al) ratio, and strongly influenced by the type of exchangeable cation present in the examined zeolite species, since the degree of Na and K exchange is generally higher than that of Ca. The ratio between divalent and monovalent cation exchange resulted to be roughly correlated to the total degree of exchange, thus suggesting that kinetic factors are involved in the monovalent vs. divalent cation exchange processes, also according to their ionic potential values.