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 investigated in a batch mode operation.

Batch adsorption studies revealed that the potential of Aleppo pine-tree sawdust in dye removal was dependant on initial pH and initial dye concentration.

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 50mg/L of AY and 1.14 × 10⁻⁴ m⁻¹ at initial concentration 15 mg/L of AY. The multilinearity obtained in the intraparticle diffusion plot showed that both film diffusion and pore diffusion are important in controlling the overall adsorption rate. The effective diffusion coefficients D_i 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 that intraparticle diffusion may not be the sole dominating factor controlling the mechanism of the process into Aleppo pine-tree sawdust. AY sorption onto sawdust was mainly located on the surface. The equilibrium isotherms were analyzed 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. © 2011 American Institute of Chemical Engineers Environ Prog, 2011