Natural and Sodium Clinoptilolites Submitted to Acid Treatments: Experimental and Theoretical Studies

In the present work, the effect of
acid treatments on the structure
of a natural and sodium exchanged clinoptilolite was evaluated using
experimental and theoretical methods. The results demonstrated the
good stability of the samples submitted to HCl treatments, although
it was proven that aluminum was extracted from the framework. It was
verified that the sodium clinoptilolite (AZ) is more resistant than
its natural form (NZ) to the acid treatment since the aluminum extraction
is smaller and the percent of estimated crystallinity is higher in
AZ. An increase in the micropore volume, as well as the creation of
new narrow micropores, was also verified. The simulation results indicated
that the aluminum at T2 position is the easiest to remove during the
dealumination process, and it was also noted that, during dealumination,
different slabs are formed in the structure, creating a framework
like a clay. Calculations suggested that the stability of the dealuminated
frameworks was related to attractive and repulsive interactions, which
take place between the species involved in the dealumination process.
Our work demonstrates that sodium modification is an essential step
to obtain a structurally stable acidic natural clinoptilolite.