T he sorption of cadmium and copper ions onto bone char has been studied. The equilibrium data have been analysed using the Langmuir and the Sips isotherm equations. A series of fixed bed sorption studies have been undertaken for the two single component systems to study the effects of various system parameters, including initial metal ion concentration, solution flowrate and bone char particle size. A new mass transfer model has been developed based on external mass transfer and surface diffusion. This model has been tested using both isotherms and incorporating a variable surface coverage. Both metal ion systems have been correlated using this diffusion model and the experimental breakthrough curves with good agreement.