Equilibrium, kinetic, and thermodynamic studies for biosorption of cadmium and nickel on grapefruit peel

The biosorption of cadmium and nickel onto grapefruit peel from aqueous solution has been investigated using batch technique. Experiments are carried out as a function of solution pH, biosorbent dosage, contact time and temperature. The equilibrium adsorption data are fitted to Langmuir and Freundlich isotherm models and the model parameters are evaluated. The Freundlich model fits the equilibrium data better than the Langmuir model. The maximum uptakes of Cd(II) and Ni(II) by grapefruit peel are found to be 42.09 and 46.13 mg/g, respectively. The kinetics of the biosorption process is found to follow the pseudo-second-order kinetic model. Thermodynamic parameters depict the endothermic nature of biosorption and the process is spontaneous and favorable. Release of cations and protons from the biosorbent during sorption of Cd(II) and Ni(II) reveals that the main sorption mechanism is ion exchange. FTIR analysis demonstrates that carboxyl and hydroxyl groups were involved in the biosorption of the metal ions. The recovery of the Cd(II) and Ni(II) from grapefruit peel is found to be more than 97% using 0.1 M HCl. The results suggest that grapefruit peel can be used effectively for the removal of Cd(II) and Ni(II) ions from wastewaters.

► Grapefruit peel shows high capacity for removing of heavy metals from wastewaters.
► The maximum uptakes are 42.09 and 46.13 mg/g for Cd(II) and Ni(II), respectively.
► The biosorption process is a feasible and endothermic process in nature.