Optimization of a cationic dye adsorption onto a chemically modified agriculture by-product using response surface methodology

In the present study, Methylene Blue (MB) removal from aqueous solutions by orange tree sawdust was optimized using the Response Surface Methodology (RSM). The effects of the intensity of the chemical treatment with NaOH, the sawdust dose, contact time and the initial MB concentration were examined in batch system. Analysis of variance (ANOVA), F-test and Student's t-test revealed that the chemical treatment concentration is the most influencing parameter, followed by the contact time, treatment dose and the initial dye concentration. An optimum treatment/adsorption point was determined for a 100% MB removal yield using MINITAB's desirability function for the recommended optimum conditions of: NaOH concentration of 0.14 M, an adsorbent dosage of 50 g/L, a contact time of 1 hour and a MB concentration of 69.5 mg/L. The physical-chemical characterization of the generated sawdust through FTIR, SEM, EDX and BET analyses showed a non negligible shift in the hydroxyl and aromatic functional groups and an important variation of the surface morphology and texture. The Kinetic and isotherm MB adsorption experiments carried out on the chemically modified sawdust demonstrated that the pseudo-second order and Langmuir models fitted very well the kinetic and at equilibrium experimental data, respectively. These findings confirm that the MB adsorption is mainly governed by a chemisorption phenomenon and was driven with a monolayer fixation process. The MB adsorption capacity of the modified sawdust was relatively important and indicates that this solid matrix could be considered as a promising material for dyes removal from industrial effluents.