Treatment influence on green coconut shells for removal of metal ions: pilot-scale fixed-bed column

This work investigates copper, nickel and zinc ion biosorption in single- and multi-component systems in a fixed-bed column using green coconut shells (CS). Approximately 85% of biosorbents are in a particle size ranging from 0.25 to 2 mm. Operational parameters selected include a flow rate of 200 mL min-1 and a bed height of 100 cm, which were selected for a shorter execution time and good adsorption capacity. Empty-bed contact time and Thomas models were applied, showing a good fit with the experimental data. The column adsorption capacity increased after the green CS powder was treated in a column with NaOH at a concentration of 0.1 mol L-1. The highest values of adsorption capacities founded were 0.69, 0.45 and 0.39 mmol L-1 for Cu(II), Ni(II) and Zn(Il), respectively, using green CS treated inside a column with NaOH of 0.1 M. The pH and chemical oxygen demand were monitored in the treatment solution and indicated that the adjustment of these parameters is necessary before disposal of these solutions. A study of desorption using an acid solution was carried out for recovery of metal ions.