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.