A theoretical model was developed by coupling mass transfer with biosorption kinetics for the removal of copper ions from aqueous solutions by Rhizopus arrhizus immobilized in sheets of porous biomass support materials. Internal mass transfer through immobilized biomass involved both convective and diffusional transport. The model also accounted for the external mass transfer limitation. The mass balance equation was solved using the orthogonal collocation method which gave the concentration of copper ions in the bulk liquid during the course of batch biosorption. The model was used for a sensitivity analysis of the system parameters and for prediction of experimental results.