## 3 Results and Discussion  
### Characterization  
Figure 1 shows the X-ray diffraction (XRD) patterns of non- and acid-modified clinoptilolite-rich tuffs. It can be observed that all samples contained clinoptilolite as the principal mineral which is defined by its main characteristic peaks at 20 = 9.85\({}^{\circ}\), 11.19\({}^{\circ}\), 22.21\({}^{\circ}\), 22.34\({}^{\circ}\), 25.96\({}^{\circ}\), and 28.09\({}^{\circ}\) according to JCPDS card 25-1349 [34]. Furthermore, comparative analysis of the XRD patterns did not show significant changes in the positions of most of the reflexions before and after the acid treatments. However, a decrease can be observed in the relative intensity of the reflexions of HCLI with the increase in sulfuric acid concentration from 0.1 to 1 M. These results suggest that the treatment of natural zeolite with H\({}_{2}\)SO\({}_{4}\) caused some structural changes and loss of crystallinity in the clinoptilolite phase. This can be attributed to dealumination of the clinoptilolite as verified by the EDS analyses [29; 35]. [PERSON] et al. [36] present the reaction mechanism which take place when the clinoptilolite-rich tuffs are  
in contact with a strong acid media (HNO\({}_{3}\)). Basically they mention the break of the primary structure of the zeolite network and the formation of Al(NO\({}_{3}\))\({}_{3}\) because the dealumination of the zeolitic material. In the present work could be a similar mechanism with the formation of Al\({}_{2}\)(SO\({}_{4}\))\({}_{3}\). The scanning electron microscopy (SEM) images of non- and acid-modified clinoptilolite-rich tuffs are shown in Figure 2. It can be observed that all of the samples presented similar morphologies and also showed the tabular and coffin shapes typical of heulandite/clinoptilolite crystals [13]. In other investigations, the morphology of synthetic zeolite as chitosan had changed [37], whereas it remained unchanged for modernite after chemical treatment [38]. This indicates that the change in morphology of the natural zeolites with acid treatment depends on the nature as well as the crystalline structure of these zeolitic materials. Table 1 shows the average chemical composition expressed in terms of % weight as obtained by EDS at different points on the surface of non- and acid-modified clinoptilolite-rich tuffs. As expected, the chemical composition changed drastically following the acid treatment of natural zeolite. A total elimination of Na\({}^{+}\) and Mg\({}^{2+}\) can be observed from the extra-framework of natural zeolite when the concentrations of H\({}_{2}\)SO\({}_{4}\) are 0.1M and 0.2M, respectively; whereas the amount of Ca\({}^{2+}\) and K\({}^{+}\) ions decrease with increasing sulfuric acid concentration as result of H\({}^{+}\) exchange or by the loss of Al\({}^{3+}\) from the zeolite network showing that its cation exchange capacity was lost. It is clear that the H\({}^{+}\) is preferentially exchanged by Na\({}^{+}\) and Mg\({}^{2+}\) from the zeolitic network rather than Ca\({}^{2+}\) and K\({}^{+}\) and this depends of the exchangeable sites that they occupy into the zeolite network [39]. It is important to mention that the Fe could be as an associated mineral (Fe\({}_{2}\)O\({}_{3}\)) of the zeolitic rock. Moreover, a significant increase in the Si/Al ratio with increasing acid concentration can be observed, due to the Al leaching from the clinoptilolite framework and the consequent loss of its crystallinity. This result is consistent with those observed by XRD analysis. Figure 3 shows the IR spectra of the non- and acid-modified clinoptilolite-rich tuffs. The spectra have been shifted by 5% from each other starting from that corresponding to Nat-CLI in order to better appreciate the differences in the absorption bands of all the materials. A broad band appears at 3446 cm\({}^{-1}\) for Nat-CLI, corresponding to the symmetric and asymmetric stretching vibration of the O-H groups, while the bending of the H-O-H vibration occurs at 1636 cm\({}^{-1}\).