The chemical behavior of natural zeolites in aqueous environments: Interactions between low-silica zeolites and 1 M NaCl solutions of different initial pH-values

A natural zeolitic material composed of microscale intergrowths of the low-silica zeolites natrolite and thomsonite (NAT/THO) was found to be more reactive in distilled water compared to the high-silica zeolites heulandite and stilbite. Relevant experiments using 1 M NaCl solutions of different initial pH-values revealed a pH increase in the acidic region and an analogous decrease in the basic region, indicating that the NAT/THO material shows a tendency to neutralize the solutions behaving either as a proton acceptor or as a proton donor. This amphoteric character is related to the H+ uptake, as well as to the OH- attack to surface reactions sites of the crystals. However, phase transformations to analcime in the base-treated low-silica zeolites were also noted. The interaction of the hydrogen ions with the aluminosilicate framework of the zeolites caused in a small extent, degradation-dissolution phenomena, resulting in surface-eroded crystals.