Film-Pore-[Concentration-Dependent] Surface Diffusion model for heavy metal ions adsorption: Single and multi-component systems

The present experimental work was performed in order to investigate the adsorption of several heavy metal ions including lead (Pb2+), cadmium (Cd2+) and nickel (Ni2+) onto a commercial kind of activated carbon (AC) in single and multi-component aqueous batch systems. Working on the equilibrium experimental data led to obtain the best-fitted isotherm model: Langmuir. The kinetic series of adsorption experiments were also performed to investigate the effects of several parameters like initial concentration, agitation speed and adsorbent dosage. In order to explain the adsorption kinetics and evaluation of the mass transfer coefficients, a diffusional kinetic model with some new suppositions was developed: the Film-Pore-[Concentration-Dependent] Surface Diffusion model (FPCDSD); a comprehensive model which could be easily reduced to describe other simplified ones. The FPCDSD model showed a high degree of correlation with the experimental data. The detailed calculation methods to determine the contribution of each resistance against mass transfer were addressed in the paper. The model with a single set of mass transfer parameters (with the order of magnitude of Dp ≈ 10−10 m2 s−1, Ds ≈ 10−15 m2 s−1 and kf ≈ 10−5 m s−1) was found successful in correlating adsorption data in ternary system under different operating conditions.