Adsorption of salicylic acid from ethanol solutions onto activated carbon: Kinetics and equilibrium studies

This work examines the removal of salicylic acid (SA) from ethanol solutions by activated carbon (AC). Batch adsorption experiments were conducted to determine adsorption kinetics and equilibrium. The adsorption capacity q e was calculated from concentration changes, and kinetics were analyzed using pseudo-first-order and pseudo-second-order models. Equilibrium data were fitted to Langmuir and Freundlich isotherms. Results showed rapid uptake of SA: over 90 % adsorption occurred within 60 min, reaching equilibrium by ∼180 min. The pseudo-second-order model fitted the kinetic data exceptionally well (R 2 ~ 0.995), whereas the pseudo-first-order model was poorer (R 2 ~ 0.86), indicating that chemisorption controls the adsorption rate. Equilibrium behavior followed the Langmuir isotherm (R 2 ~ 0.993), yielding a high monolayer capacity (∼85 mg g −1 ). The Freundlich model was less suited (R 2 ~ 0.89), suggesting relatively uniform binding sites on the carbon. A Weber–Morris diffusion plot showed a two-stage uptake (initial film diffusion and slower intraparticle diffusion). These findings demonstrate that activated carbon effectively adsorbs SA from ethanol, with kinetics and capacity comparable to aqueous systems. • Activated carbon effectively adsorbs salicylic acid from ethanol solutions. • Kinetic data fit the pseudo-second-order model (R 2 > 0.99), indicating chemisorption. • Equilibrium adsorption follows the Langmuir isotherm (monolayer capacity). • High maximum capacity (∼85 mg g −1 ) demonstrates strong affinity of AC for SA. • Intraparticle diffusion analysis reveals a two-stage adsorption process.