Optimization of Acid Blue 113 Adsorption from Aqueous Solutions by Natural Bentonite Using Response Surface Model: Isotherm and Kinetic Study

Background & objectives: Dyes are one of the main environmental pollutants of textile industrial wastewater which are toxic, carcinogenic, mutagenic, and non-biodegradable. Therefore, in this study, Response Surface Methodology (RSM) was used to investigate the operational parameters and determine the optimum conditions for the removal of acid blue 113 in the presence of bentonite. Methods: The structure and morphology of bentonite adsorbent was investigated by XRD, FESEM and XRF techniques. Experiments were carried out as central composite design with four input parameters namely reaction time, initial pH, adsorbent dosage and initial concentration of dye at three levels. Adsorption isotherms and kinetics model were investigated to evaluate the adsorption process in different concentrations. Results: The results of physical-chemical analysis confirmed the structure of bentonite. The proposed model (Quadratic) was confirmed with high correlation coefficient (R2=0.9872 and R2Adj=0.9724) indicated that the experimental and predicted results were very consistent with the model. Finally, under optimal conditions (initial concentration=10.32 mg/L, absorbent dose=0.53 g/L, reaction time=82.94 min and pH=3.06) the removal efficiency was 98.62% with a desirability of 0.945 for acid blue 113. Adsorption isotherm and kinetic studies indicated that adsorption process followed Freundlich isotherm (0.9216), whereas the kinetic model found to fit well with pseudo-second-order kinetics (0.9985). Conclusion: The present study demonstrated that natural bentonite absorbent had high ability to remove acid blue 113. In addition, the central composite design could be used as an effective method to optimize the dye adsorption from industrial wastewater containing high concentrations of dye.