Modeling of the adsorption kinetics of zinc onto granular activated carbon and natural zeolite

The isotherms and kinetics of zinc adsorption from aqueous solution onto granular activated carbon (GAC) and natural zeolite were studied using an agitated batch adsorber. The maximum adsorption capacities of GAC and natural zeolite to- wards zinc(II) from Langmuir adsorption isotherms were determined using experi- mental adsorption equilibrium data. The homogeneous solid diffusion model (HSD-mo- del) combined with external mass transfer resistance was applied to fit the experimental kinetic data. The kinetics simulation study was performed using a computer program based on the proposed mathematical model and developed using gPROMS. As the two-mass transfer resistance approach was applied, two model parameters were fitted dur- ing the simulation study. External mass transfer and solid phase diffusion coefficients were obtained to predict the kinetic curves for varying initial Zn(II) concentration at con- stant agitation speed and constant adsorbent mass. For any particular Zn(II) - adsorbent system, kf was constant, except for the lowest initial concentration, while Ds was found to increase with increasing initial Zn(II) concentration.