Abstract
The adsorption performance of milk thistle seeds (MTS), a low-cost and locally available biomaterial, for methylene blue (MB) removal from aqueous solutions was examined using a batch process. The effects of operational conditions such as initial dye concentration (50-250 mg/L), adsorbent dose (0.1-0.8 g/200 mL), temperature (25 degrees C-45 degrees C), ionic strength (0-500 mg/L) and pH 3-11 on the uptake of MB by MTS were examined. The adsorption of MB is favored by low temperatures. The ionic strength disfavors the sorption of dye. Near neutral and basic pHs are more favorable for the dye adsorption. Three models were employed to describe experimental adsorption isotherm data: Langmuir, Freundlich and Temkin equations. Experimental equilibrium data were best represented by the Freundlich isotherm model. The thermodynamic parameters such as Delta G degrees, Delta H degrees and Delta S degrees were determined for the adsorption of MB. The removal kinetics of MB by MTS was analyzed using the pseudo-first-order, pseudo-second-order model equations and intraparticle diffusion model. Pseudo-second-order model was found to describe the adsorption process better than the pseudo-first-order equation. Analysis of adsorption kinetic results indicated that both film-and particle-diffusion are effective adsorption mechanisms. The results of the present work indicated that MTS was an attractive candidate for removing cationic dyes from wastewater.