Time evolution of a natural clinoptilolite in aqueous medium:: conductivity and pH experiments

The chemical behavior in an aqueous medium of a natural zeolitic material, NZ (mainly consisting in crystals of the zeolites clinoptilolite/heulandite) has been studied through electrochemical techniques, complemented by atomic absorption spectrometry. The time dependence of the conductivity of the aqueous medium in the presence of NZ, showed a steep increase at the beginning followed by a slower increase for longer times until saturation of the system is reached. The release of the ions present in the zeolitic material at different times, was followed by means of atomic adsorption spectroscopy, which indicated that the sodium ion is the main responsible for the conductivity response. The interaction of NZ with the aqueous medium revealed a pH increase in the weakly acid region and a decrease in the basic region. The correlation between conductometric and pH-metric studies suggests that an ion-exchange mechanism takes place within the very first minutes of the interaction of NZ with the aqueous medium, followed by the temperature-dependent dissolution of minority phases up to several days. Finally, a comparative study between NZ and a modified form of this zeolite with sodium carbonate (NZ1), showed a faster pH increase with time for NZ1. (C) 2000 Elsevier Science B.V. All rights reserved.