## 3 Results and Discussion  
### Sample Characterization  
The XRPD patterns of CLI and PHI samples are reported in Figure 2A,B. The CLI sample contains clinoptiolite as the only exchanger phase, while the PHI sample is more heterogeneous, containing at least three zeolitic exchangers, mainly phillipsite with minor amounts of chabazite and analcime. Quantitative X-ray analysis carried out using the RIR/Rietveld method supplied the following mineralogical composition: 79% clinoptiolite, 5% feldspar, 1% quartz, 15% clays minerals for CLI and 44% phillipsite, 4% chabazite, 10% analcime, 32% feldspar, 20% clays minerals for PHI, respectively. Concerning the clinoptiolite sample, XRPD analysis confirms that the sample consists of clinoptiolite  
Figure 2: XRPD characterization of clinoptiolite-rich twff (CLI) (**A**) and phillipsite-rich twff (PHI) sample (B). CM = Clay Minerals, C = Clinoptiolite, P = Phillipsite, F = feldspar, Q = quartz, A = analcime. as the only phase with exchange properties. Therefore, the CLI sample can be considered as a single exchanger containing only 21% of non-exchanging phase. Concerning the PHI sample, the analysis underlined its heterogeneity, although phillipsite is the zeolite present in the maximum concentration. The second zeolite in order of abundance, the analcime, has a much denser microstructure than the other two (phillipsite and chabazite), which makes its contribution to the exchange process negligible, at least up to the end of our experiments. The last zeolitic phase, chabazite, is present in a very low concentration. This makes it possible to describe the PHI sample as a single exchanger phase with a Si/Al ratio of 2.38. Table 1 reports the chemical analysis after acid digestion of the selected samples. Although it is a bulk analysis, it is possible to highlight how the CLI sample is mainly a potassic/calcic tuff, while PHI is a potassic/sodic/calcic tuff. This is perfectly in agreement with the genesis and origins of the two selected tuffs. The CEC of the two samples was 1.97 meg g\({}^{-1}\) and 2.03 meg g\({}^{-1}\) for CLI and PHI, respectively. These relatively close values arise from the higher cation content of the phillipsite in the PHI sample that compensates for its amount, which is lower than that of clinoptilolite in the CLI sample. The ECEC values were 0.142 meg g\({}^{-1}\) and 0.130 meg g\({}^{-1}\), for CLI and PHI, respectively. Such values are for both materials roughly 1 out of 10 of the total exchange capacity, which accounts for the surface/bulk ratio of the tuff grains. Finally, the AEC values obtained for the four samples are: CLI-Br = 0.142 meg g\({}^{-1}\); CLI-Cl = 0.071 meg g\({}^{-1}\); PHI-Br = 0.115 meg g\({}^{-1}\); PHI-Cl = 0.058 meg g\({}^{-1}\). The data show the following evidence:  
* The AEC value of both HDTMA-Br modified samples is about equal to the ECEC values: this indicates that a double layered micelle is formed on the zeolite surface;
* On the contrary, the AEC value of both HDTMA-Cl modified samples is lower than the ECEC values: in this case, a patchy bilayer is formed on the zeolite surface. This demonstrates that the counterion affects the micelle formation more than the zeolite present in the sample: even if the genesis and structure of the two tuffs are different, the morphology of the zeolites present is almost the same, characterized by a rigid framework with internal channels oriented along two preferential directions (planar-like structure). This type of morphology, together with the high Si/Al ratio typical of these natural zeolites, leaves many free surfaces available to interact with large surfactant molecules, which, however, cannot access the most internal cationic sites of the zeolitic framework, but are able to micellize on the surface of the same tuffs. The obtained results are confirmed by previous experiments in which a clinoptilolite-rich sample coming from New Mexico was also used [31; 42].