## 4 Conclusions  
This study investigated the potential of 4 AZWto remove two basic cationic dyes, MB and MG, from aqueous solutions under batch experimental conditions. It was observed that adsorption depends on the pH, adsorbent dose, contact time, and initial dye concentration. It is interesting to note that the initial solution pH is one of the key parameters in the MB and MG adsorption performance; the presence of salt in the solution decreased the adsorption by competitive inhibition. According to kinetic data, the adsorption process could be defined by a pseudo-second-order kinetic model. The Langmuir model represented both systems (4 AZW-MB and 4 AZW-MG) giving maximum adsorption capacity (qmax) values of 9.95 mg/g and 45.64 mg/g, respectively, at 25 \({}^{\circ}\)C. A thermodynamic study revealed that the adsorption was spontaneous, endothermic, and physical in nature. The analysis of our results performed by the Box-Behnken Design (BBD) for the adsorption of MB on 4 AZW allowed us to define the corresponding optimum conditions: More than 99.09% MB removal with pH = 9; 4 AZW load = 0.06 g in 50 mL; initial MB concentration = 8 mg/L and 70 min removal time at 25 \({}^{\circ}\)C.  
Thus, the large amounts of 4A zeolite generated as solid waste by the natural gas dehydration units after several treatment cycles of the gas can be efficiently used as an adsorbent for these cationic dyes, without any specific treatment. Although it is well known \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Dye** & **T (K)** & **SD** & **K\({}_{\mathrm{L}}\) (L/mg)** & **K\({}_{\mathrm{L}}^{\mathrm{o}}\)(\(\mathrm{\times}\)10\({}^{\mathrm{o}}\))** & **Ln K\({}_{\mathrm{L}}\)\({}^{0}\)** & **\(\Delta\)G\({}^{0}\)** & **\(\Delta\)H\({}^{0}\)** & **\(\Delta\)S\({}^{0}\)** \\  & & & & **(Dimensionsless)** & **(d/mol)** & **(d/mol)** & **(d/mol)** & **(j/mol.K)** \\ \hline \multirow{4}{*}{MB} & 298 & 0.241 & 4.45 \(\pm\) 0.54 & 1.42 \(\pm\) 0.20 & 14.16 \(\pm\) 0.14 & \(-\)35.41 \(\pm\) 0.37 & \multirow{4}{*}{18.68 \(\pm\) 1.37} & \multirow{4}{*}{180.64 \(\pm\) 4.09} \\  & 303 & 0.287 & 5.24 \(\pm\) 0.68 & 1.67 \(\pm\) 0.25 & 14.33 \(\pm\) 0.15 & \(-\)36.04 \(\pm\) 0.40 & \\ \cline{1-1}  & 313 & 0.338 & 6.71 \(\pm\) 0.75 & 2.14 \(\pm\) 0.28 & 14.57 \(\pm\) 0.13 & \(-\)37.85 \(\pm\) 0.37 & \multirow{4}{*}{18.68 \(\pm\) 1.37} & \multirow{4}{*}{180.64 \(\pm\) 4.09} \\  & 323 & 0.399 & 7.96 \(\pm\) 0.70 & 2.54 \(\pm\) 0.27 & 14.75 \(\pm\) 0.11 & \(-\)39.65 \(\pm\) 0.31 & \\ \hline \multirow{4}{*}{MG} & 298 & 0.315 & 4.34 \(\pm\) 0.20 & 1.58 \(\pm\) 0.10 & 14.27 \(\pm\) 0.07 & \(-\)35.41 \(\pm\) 0.19 & \multirow{4}{*}{25.53 \(\pm\) 1.12} & \multirow{4}{*}{204.53 \(\pm\) 3.28} \\  & 303 & 0.214 & 5.47 \(\pm\) 0.37 & 1.99 \(\pm\) 0.17 & 14.50 \(\pm\) 0.09 & \(-\)36.43 \(\pm\) 0.24 & \\ \cline{1-1}  & 313 & 0.384 & 7.20 \(\pm\) 0.28 & 2.62 \(\pm\) 0.15 & 14.78 \(\pm\) 0.06 & \(-\)38.48 \(\pm\) 0.18 & \\ \cline{1-1}  & 323 & 0.299 & 9.84 \(\pm\) 0.44 & 3.59 \(\pm\) 0.23 & 15.09 \(\pm\) 0.06 & \(-\)40.52 \(\pm\) 0.20 & \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Thermodynamic parameters for adsorption of MG and MB onto 4 AZW. that zeolite is not a renewable natural resource, its use as an adsorbent has both practical and cost-effective advantages. Conceptualization, A.I., S.C. and L.M. ; methodology, A.I., S.C., A.A. ([PERSON]) and L.M. ; software, L.B. and A.T.; validation, J.-C.B., L.B., A.T., A.A. ([PERSON]), A.E.J. and L.M. ; formal analysis, J.-C.B., L.B. and A.T.; investigation, A.I., A.A. ([PERSON]), L.B. and L.M. ; resources, A.A. ([PERSON]) and L.M. ; data curation, A.I., S.C.; writing--original draft preparation, A.I., S.C.; writing--review and editing, A.I., A.A. ([PERSON]), A.B., A.A. ([PERSON]) and L.M. ; visualization, A.I., S.C., L.B. and J.-C.B. ; supervision, J.-C.B. [PERSON] L.M. and A.A. ([PERSON]); project administration, L.M., A.A. ([PERSON]), A.E.J. ; funding [PERSON], A.E.J. All authors have read and agreed to the published version of the manuscript.