Diffusional mass transfer model for the adsorption of food dyes on chitosan films

Abstract

The adsorption kinetics of erythrosine B and indigo carmine on chitosan films was studied by a diffusional mass transfer model. The experimental curves were obtained in batch system under different conditions of stirring rate (80–200 rpm) and initial dye concentration (20–100 mg L−1). For the model development, external mass transfer and intraparticle diffusion steps were considered and the specific simplifications were based on the system characteristics. The proposed diffusional mass transfer model agreed very well with the experimental curves, indicating that the surface diffusion was the rate limiting step. The external mass transfer coefficient (kf) was dependent of the operating conditions and ranged from 1.32 × 10−4 to 2.17 × 10−4 m s−1. The values of surface diffusion coefficient (Ds) increased with the initial dye concentration and were in the range from 0.41 × 10−14 to 22.90 × 10−14 m2 s−1. The Biot number ranged from 17.0 to 478.5, confirming that the intraparticle diffusion due to surface diffusion was the rate limiting step in the adsorption of erythrosine B and indigo carmine on chitosan films.