ADSORPTION OF SALICYLIC ACID BY WHEAT STRAW BIOCHAR: KINETICS, ISOTHERM AND THERMODYNAMIC STUDIES

摘要

To remove salicylic acid from aqueous solutions, Biochars (BC300, BC400 and BC500) as a low-cost adsorbent derived from wheat straw was pyrolyzed under different temperatures, characterized by surface area determination, CHN elemental analysis, FTIR spectroscopy, scanning electron microscopy and X-ray diffraction. Batch sorption studies were carried and the adsorption kinetics, isotherm and thermodynamic were investigated. The results showed that pseudo second-order kinetics were the best model (R2>0.99) for describing the adsorption of salicylic acid onto biochars. Equilibrium data were well fitted to the Langmuir (R2> 0.9779) and Freundlich (R2 > 0.9264) isotherm models. The maximum monolayer coverage capacity (Qm) was calculated according to the linear form of the Langmuir equation was 60.24 mg.g-1 for BC300, 50.25 mg.g-1 for BC400, 30.67 mg.g-1 for BC500 and 21.83 mg.g-1 for BC600. The values of Qm increased with operating temperatures among four adsorbents. Various thermodynamic parameters such as Gibbs free energy (AG0), enthalpy (AH°), and entropy (A50) changes were computed, and the data showed that the sorption process of salicylic acid solution onto BC300, BC400 and BC500 were spontaneous and endothermic but that they were spontaneous and exothermic for BC600.