A model for pH dependent equilibrium of heavy metal biosorption

Biosorption of heavy metals can be an effective process for the removal and recovery of heavy metal ions from aqueous solutions. The biomass of marine macro algae has been reported to have high uptake capacities for a number of heavy metal ions and the uptake capacities are strongly influenced by th e value of the solution pH. In this paper, a modified Langmuir model was pr oposed for describing the pH dependent biosorption equilibrium and validate d with isotherm data obtained from batch experiments and from the literatur e. The model assumes that the functional groups for heavy metal interaction s are weakly acidic and the uptake capacities of the biomass are affected t hrough the association and dissociation equilibrium between two apparent io nic forms. The model equations fitted the experimental data well, which sup ports the biosorption mechanism proposed.