Determination of solid-phase loading for the removal of metal ion from effluents using fixed-bed adsorbers

The sorption of cadmium and copper ions from aqueous solutions onto bone char using fixed-bed adsorbers has been studied. A film pore diffusion model has been utilized to predict theoretical breakthrough curves, which are compared with experimental breakthrough curves by means of error analysis. The key parameters for correlating the theoretical model are the external film mass-transfer coefficient (k_f), the effective diffusion coefficient (D_eff), and the solid-phase loading (q). The k_f is determined from fixed-bed empirical correlations, and D_eff is determined by a best-fit optimization routine. The q value has traditionally been determined using the equilibrium isotherm, which is applicable when the column adsorbent reaches equilibrium, or using the breakthrough curve mass balance when the column does not reach equilibrium. The breakthrough curve mass balance method needs experimental curves for each system and is not a practical solution for general design models. This paper presents two novel predictive equations for q in terms of process variables. The accuracy of the equations is sufficient for application in design models for nonequilibrium and equilibrium systems.