Application of film-pore diffusion model for methylene blue adsorption onto plant leaf powders

In the present work kinetics of methylene blue adsorption onto three low-cost adsorbents namely guava leaf powder (GLP), teak leaf powder (TLP) and gulmohar leaf powder (GUL) was predicted using film-pore diffusion model. The model equations were solved numerically by method of lines using Excel. Initial estimates of mass transfer parameters namely external-film transfer coefficient and internal diffusion coefficient were obtained using single resistance models at temperatures 303, 313 and 323 K and for initial dye concentrations 50, 100, 150 and 200 mg dm−3. Film-pore diffusion model was then used to determine the concentration-independent values of these mass transfer coefficients. Thus, external-film transfer coefficients were found to be in the range of 3 × 10−6 to 35 × 10−6 m s−1, 1 × 10−6 to 8 × 10−6 m s−1 and 1 × 10−6 to 11 × 10−6 m s−1 for guava, teak and gulmohar leaf powders, respectively, in the chosen temperature range. At the same time internal diffusion coefficients were in the range of 0.1 × 10−12 to 1.9 × 10−12 m2 s−1, 0.1 × 10−12 to 0.6 × 10−12 m2 s−1 and 0.2 × 10−12 to 1.3 × 10−12 m2 s−1 for guava, teak and gulmohar leaf powders, respectively. It was evident that film-pore diffusion model could satisfactorily describe kinetics of methylene blue adsorption onto the three low-cost adsorbents used.