Mass-transfer processes in the adsorption of cationic dye by sawdust

Abstract

Adsorption kinetic and equilibrium studies of cationic dye namely, Astrazon Yellow (AY) from aqueous solution at various initial dye concentration (15–50 mg/l), pH (2–9), particle size <1600 μm on Aleppo pine-tree sawdust were studied in a batch mode operation. Batch studies revealed that the potential of Aleppo pine-tree sawdust in dye removal was dependant on initial pH and initial dye concentration. In order to select the main rate-limiting step in the overall uptake mechanism, a single external mass transfer diffusion model, Urano and Tachikawa model and intraparticle diffusion model were used. The external mass transfer rate constant β was found to be 8.5 10-5 m-1 at initial concentration 50 mg/l of AY and 1.14 10-4 m-1 at initial concentration 15 mg/l of AY. It was observed multi-linearity in the shape of the intraparticle diffusion plot. The two phases in the intraparticle diffusion plot suggest that the sorption process proceeds by surface sorption and an intraparticle diffusion stage. The effective diffusion coefficients Di were found to be 3.88 10-11 cm2/s and 4.2 10-11 cm2/s for initial concentration of AY of 15 mg/l and 50 mg/l respectively, indicating a poor intraparticle diffusion into Aleppo pine-tree sawdust . AY sorption onto sawdust was mainly located on the surface. The equilibrium isotherms were analysed using the Langmuir, Freundlich, Temkin and Elovich models. It was seen that the sorption data fitted to Langmuir, Freundlich, Temkin and the Elovich isotherms, but they were very well described by the Langmuir model.