The sorption of binary mixtures of copper/cadmium and copper/zinc ions onto bone char was studied in fixed beds. The effects of solution flow rate, initial dye concentration, and bone char particle size range were investigated. A mass transport model based on film-surface diffusion and the IAS model for the equilibrium relationship was used to develop theoretical fixed-bed breakthrough curves. The model incorporates the Sips isotherm for the first time in fixed-bed predictions, since this isotherm gives an excellent correlation of the experimental equilibrium data. The model was used to determine the optimum surface diffusivities as 7.37 x 10(-10) and 2.73 x 10(-9) cm(2)/s for copper and cadmium in the Cu/Cd system; and 1. 61 x 10(-9) and 2.43 x 10(-9) cm(2)/s for copper and zinc in the Cu/Zn system. (C) 2004 American Institute of Chemical Engineers.