Adsorptive removal of cobalt ions on raw and alkali-treated lemon peels

Batch-wise biosorption of Co(II) from aqueous cobalt nitrate solution of different concentrations has been carried out on raw and NaOH-treated lemon peels. They were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, thermogravimetric analysis and Brunauer- Emmett-Teller surface area analysis. The influence of biosorbent dose, pH, contact time and temperature on the adsorption process has been studied. Maximum adsorption was observed at pH 6. The equilibrium adsorption on raw and NaOH-treated lemon peels was achieved in 150 and 210 min, the maximum adsorption capacity being 20.83 and 35.71 mg/g, respectively. Energy-dispersive X-ray spectroscopy and desorption study confirmed that the mechanism of adsorption is ion exchange. The Langmuir isotherm and pseudosecond-order kinetic model gave the best fit for the adsorption of Co(II). The desorption was found to be more than 96 % using 0.1 N HCl, and the adsorbent could be reused three times with intermediate alkaline regeneration stage. Experiments to establish the effect of competing metal ions on biosorption capacity were also performed. Thus, NaOH-treated lemon peels have shown the potential as a good biosorbent for treating industrial wastewater at low cobalt concentration.