Removal of heavy metals (Cu, Pb) from aqueous solutions using pine (Pinus halepensis) sawdust: Equilibrium, kinetic, and thermodynamic studies

Natural Pinus halepensis sawdust has been explored as an alternative biosorbent of heavy metals from aqueous solutions. The effects of pH, adsorbent dose, contact time, metal concentration, and temperature on copper and lead sorption efficiency were investigated through batch experiments. The optimum pH range was 5-8 for Pb and 7 for Cu. Optimum adsorbent dose, achieving almost complete Cu and Pb removal was 10 g/L. Contact times at which maximum metal adsorption was achieved ranged between 5 min to 24 h. An increase in initial metal concentration had varying impacts yet always resulted in increased adsorption capacity. Equilibrium adsorption data were best fitted with Freundlich isotherm for Cu while Pb experimental data fitted equally both Freundlich and Generalized isotherm models. Metal adsorption kinetics was very well described by the pseudo second-order model. Higher metal removal efficiencies and improved equilibrium adsorption capacity were observed at higher temperature. The adsorption process was not spontaneous for Cu, and for Pb at lower temperatures. Adsorption was an endothermic chemical process and the positive values of AS suggest an increase in randomness at the solid/liquid interface during adsorption. (C) 2018 Elsevier B.V. All rights reserved.