Sorption of malachite green by a novel sorbent, dead leaves of plane tree: Equilibrium and kinetic modeling

In the present study, the dead leaves of plane tree (Platanus vulgaris) were investigated as a novel biosorbent of dyes taking aqueous malachite green solutions as a model system. Kinetic data and sorption equilibrium isotherms were carried out in batch process. The effect of different experimental conditions such as contact time, sorbent dose, initial concentration of dye, agitation speed, ionic strength, and temperature on the kinetics of malachite green removal was studied. Modeling of kinetic results shows that sorption process is best described by the type I expression of the pseudo-second order model. The sorption rate constant, the sorption equilibrium capacity, and the initial sorption rate were functions of the sorbent dose, the initial concentration, the temperature, and the ionic strength. The agitation speed showed a limited influence on the removal kinetics. The activation energy of the sorption process was also calculated. The malachite green uptake process was found to be controlled by pore diffusion. The average intraparticle diffusion coefficient (DO) was calculated and found to be 6.03 x 10(-4) min(-1). Equilibrium isotherm data could be well described by both the Langmuir and Freundlich models, but the Langmuir expression fits the equilibrium data better. The five Langmuir linear equations were discussed. The effect of temperature on the sorption isotherms of dye has been also studied and the thermodynamic parameters Delta G degrees, Delta H degrees, and Delta S degrees were determined. (C) 2007 Elsevier B.V. All rights reserved.