Influence of extraction techniques on the adsorption capacity of methylene blue on sawdust: Optimization by full factorial design

Wood wastes have been widely studied for their adsorption properties in recent years. Researchers have mainly been interested in Atlas cedar sawdust. The present work studies four adsorbents after different extraction (hydrodistillation, soxhlet, maceration, and ultrasound) for methylene blue adsorption. The points discussed concern the operating conditions used during adsorption, thermodynamic, kinetic and other models describing the adsorbent-adsorbate system, and the effect of the main operating parameters (adsorbate concentration, treatment pH, and adsorbent concentration) was investigated using the full factorial design. The best adsorbent is the residue of sawdust generated after extraction via maceration: the yield of methylene blue adsorption is 98.42 % and the adsorbed quantity (Q_ads = 7.84 mg/g) is close to that of powdered activated carbon used for comparison (Q_ads = 9 mg/g). According to the kinetic result, the second order describes well the adsorption of MB onto the four types of Cedar Sawdust. The thermodynamic study confirms the physisorption process in which the enthalpy was found low to 40 kJ·mol⁻¹.