Binary metal sorption on bone char mass transport model using IAST

The binary sorption of Cu-Cd, Cd-Zn, and Cu-Zn onto bone char has been studied using an equilibrium and batch agitation system. The sorption capacities and the selectivity of metal ions onto bone char follows the order Cu²⁺ > Cd²⁺ > Zn²⁺, which is in the reverse order of the hydrated ionic radii. The binary sorption equilibria were predicted by the ideal adsorbed solution theory (IAST) on the basis of single component isotherm data using a Langmuir or Langmuir-Freundlich isotherm. The overall performance of the IAST provides a reasonable curve fitting to the experimental data. The single component film-pore diffusion model was extended to the multicomponent systems to correlate the batch kinetic data by incorporating the shrinking core model and the IAST. All the diffusivities in the binary systems are similar to or less than the pore diffusivities in single component systems.