Abstract

Background: Conserving water for human survival and providing future security are important issues that need to be addressed. Methods: In this study, a zeolite modified with hexadecyl trimethyl ammonium bromide (HDTMA-Br), a cationic surfactant, and its application in removing direct blue 129 (DB129) was examined. Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) were used to characterize both modified and unmodified zeolites. The effects of operational parameters such as the amount of adsorbent, initial dye concentration and pH on the removal efficiency of the dye were examined. Results: The results showed that in the initial dye concentration of 50 mg/L, the optimum amounts of adsorbent and pH were 0.3 g and 7, respectively. Increasing the dye concentration from 20 to 100 mg/L resulted in the reduction of the removal efficiency from 100% to 79% in the contact time of 90 minutes. The results indicated the highest attracting correlation with Langmuir model. The maximum adsorbent capacity obtained from Langmuir model was 25 mg/g. The kinetics of the dye adsorption on the modified zeolite followed pseudo-second-order kinetics model. Calculated thermodynamic parameters showed that Gibbs free energy changes (DGo) at temperatures of 20 and 45°C were -29.41 and -35.20 kJ/mol, respectively. Enthalpy (DHo) and entropy changes were equal to 41.181 kJ/mol and 0.241 J/mol K, respectively. The results showed that the processing was a spontaneous endothermic reaction. The process modeled by artificial neural networks (ANN) showed that the experimental results can be accurately modeled using neural network model. The correlation coefficient found between the experimental and the model results was 0.951. Conclusion: Due to the low cost, high abundance and availability of zeolite, the removal efficiency of this adsorbent can be increased to desirable levels by modifying.

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