Mango seed, an abundant residue of the food industry, was used in its natural form (MS) and protonated form (AMS) as a biosorbent for the removal of Victazol Orange 3R (VO-3R) dye from its aqueous solutions. These biosorbents were characterized by infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and by nitrogen adsorption/desorption curves. Optimization of the effects of the initial pH of the dye solution, biosorbent dosage and contact time between the dye and the biosorbents on the biosorption capacities of the biosorbents was studied. Based on an error function (F-error), the general order kinetic model provided the best fit to the experimental data when compared to the pseudo-first order and pseudo-second order kinetic biosorption models. The equilibrium data were fitted to Langmuir, Freundlich and Liu isotherm models. For both biosorbents, the equilibrium data were best fitted to the Liu isotherm model. Finally, the mechanism of biosorption involving VO-3R and lignin-cellulose was evaluated using the hybrid quantum mechanical/molecular mechanical (QM/MM) approach and molecular dynamic (MD) simulations. The results suggest that water molecules play a key role in the biosorption process. (C) 2012 Elsevier B.V. All rights reserved.