## 3 Results and Discussion
### Syntheses by the Conventional Hydrothermal Method  
The study of syntheses using light ash from mineral coal as the primary source of Si and Al was carried out, modifying parameters such as the stirring time, Na/T ratio, OH/T ratio (where T = Si + Al), synthesis time, the temperature of agitation of the synthesis gel, the sonochemical treatment, and the alkaline fusion of the residue. Table 2 shows the general picture of the changes made in the study of the syntheses of the LTA-type zeolite samples using fly ash. The materials are denoted as ZACF (Zeolite A from Coal Ash) plus the number of the experiment. \begin{table}
\begin{tabular}{c c} \hline \hline
**Component** & **(\%)** \\ \hline Na\({}_{2}\)O & 1.50 \\ MgO & 2.00 \\ Al\({}_{2}\)O\({}_{3}\) & 24.09 \\ SiO\({}_{2}\) & 54.25 \\ K\({}_{2}\)O & 4.03 \\ CaO & 2.60 \\ TiO\({}_{2}\) & 1.75 \\ Fe\({}_{2}\)O\({}_{3}\) & 8.12 \\ Others & 4.26 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Composition of the CF residue. Figure 2: (a) X-ray diffractogram of the CF residue where m—mullite and q—quartz, and (b) SEM image of the CF residue. Comparing the ZACF-1 and ZACF-2 samples with the standard LTA (Figure 3), the variation of the Na/T and OH/T ratios in the synthesis gel did not lead to the formation of the LTA structure (the crystallinities of the samples were below 20%). In Figure 3b, the diffractogram demonstrates the effect of the crystallization time; small peaks indicative of the LTA zeolite appear after 4 h in the ZACF-2 sample. The quartz and multite that did not dissolve can be observed, and this dissolution is necessary for the formation of the zeolitic structure. At longer times, there is no increase in the dissolution of these phases, but rather sodalite appears, which is a more stable zeolitic phase than LTA. Quartz is a very stable phase, and therefore, remains in the product; for its complete dissolution, an alkaline fusion is necessary [21]. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **Gel Stirring Time** & **Resolute** & **Reflux at** & & & **Time Studied** \\  & **(min/Temperature** & **Ultrasonated** & **80 °C for** & **Al Added \({}^{*}\)** & **Na/T Ratio** & **OH/T Ratio** & **(h)** \\  & (°C) & **30 min** & **120 min** & & & & \\ \hline LTA & 30/25 & - & - & - & 1.6 & 1.25 & 4 \\ ZACF-1 & 30/25 & - & - & - & 1.6 & 1.25 & 2, 4, 6, 24, 48 \\ ZACF-2 & 30/25 & - & - & - & 2.0 & 1.66 & 2, 4, 6, 24, 48 \\ ZACF-3 & 120/80 & - & Yes & - & 1.6 & 1.25 & 2, 4, 6, 24, 48 \\ ZACF-4 & 120/80 & Yes & Yes & - & 1.6 & 1.25 & 2, 4, 6, 24, 48 \\ ZACF-5 & 120/80 & Yes & Yes & Yes & 1.6 & 1.25 & 2, 4, 6, 24, 48 \\ ZACF-6 & 120/80 & - & Yes & Yes & 1.6 & 1.25 & 2, 4, 6, 24, 48 \\ \hline \hline \end{tabular}  
* Sodium aluminate added after 120 min of stirring under reflux. After adding the aluminate, the reaction remained under stirring at reflux for another 30 min.  
\end{table} 
Table 2: Nomenclature and parameters studied for the samples. Figure 3: X-ray diffractogram of (**a**) ZACF-1, (**b**) ZACF-2, and (**c**) ZACF-3 zeolites; where: m—mullite, q—quartz, sa—SAPO, p—zeolite P, s—sodalite, x—zeolite X, a—zeolite LTA. In the ZACF-3 and ZACF-4 samples, the synthesis gel was refluxed at 80 \({}^{\circ}\)C for 120 min under magnetic stirring. In the ZACF-4 sample, the fly ash residue was also subjected to a sonochemical treatment. The X-ray diffractograms for these samples are shown in Figures 3c and 4a. The increase in temperature and the sonochemical treatment favor the formation of the LTA zeolite after 2 h of crystallization. At longer times, more stable phases are observed, such as sodalite (20 = 13.96), P (20 = 17.8; 28.02; and 33.38), and Chabasite (20 = 24.2), leading to a decrease of the crystallinity of the LTA zeolite. The quartz and multite phases were not fully dissolved. The crystallinity of the product obtained in the ZACF-4 samples was below 20%, and there was no formation of the desired zeolitic phase in the ZACF-3.