Application of branched-pore diffusion model in adsorption of reactive dyes on activated carbon

In this work, the branched pore diffusion model (BPDM) was applied to the single component adsorption of three reactive dyes on activated carbon in a batch stirred vessel. Results are in terms of theoretical concentration decay curves, characterised by the non-linear combination of four mass transfer parameters namely the external mass transfer coefficient k(f), the solid diffusivity D-s, the micropore rate coefficient k(b) and the fraction micropores f. An 'improved' solution technique was presented where an optimising subroutine was employed to select 'best' combination of the mass transfer parameters. Compared to the existing methods, this yielded more accurate results over a longer period of adsorption and shorter computational time. Also, equilibrium was accurately described by the Fritz-Schlunder isotherm. Results showed that, over a wide range of system conditions, a single k(f), k(b) and f value described each dye/carbon system; while D-s increased with the initial solution concentration, C-0. Furthermore, D-s was mathematically related to the surface loading q(s). This paper provides an in-sight into the relation between the sorbent surface, the solute properties and the adsorptive characterictics. (C) 2001 Elsevier Science B.V. All rights reserved.