Ricerc@Sapienza

This study deals with the evaluation of the single and binary removal of Pb2+ and Cd2+ from aqueous solutions using HNO3 modified olive pomace (N-OP) as a biosorbent, as well as the development of a renovative model for the binary adsorption isotherm. The biosorbents were characterized and batch adsorption experiments were used to investigate the optimum conditions for pH, adsorbent dose, and contact time. The effect of the initial metal ion concentration, pH, ionic strength, and temperature on the adsorption of the single Pb2+ and Cd2+, and their varying initial metal ion concentration ratios on the binary adsorption from the bimetallic systems were evaluated. The reuse capacity of the biosorbent was confirmed with four consecutive adsorption and desorption cycles. The kinetic studies indicated that the adsorption of Pb2+ and Cd2+ followed a pseudo-second-order model. The N-OP displayed equilibrium adsorption capacities of 64 mg g-1 for Pb2+ and 20.5 mg g-1 for Cd2+ from the single metal ion solutions using 1.0 g L-1 N-OP at the optimum pH of 5.5 and 6.0, respectively. The results were best fitted with the Langmuir model for Pb2+ and Radke-Prausnitz model for Cd2+ adsorption at 25°C. The themodynamic study showed that the adsorption of Pb2+ was exothermic and that of Cd2+ was an endothermic process. For the specific binary adsorption behavior, an extended isotherm model was developed based on the addition of the single adsorption contributions of Pb2+ and Cd2+ calculated from binary data. The existence of Cd2+ in a binary solution increased Pb2+ removal while the existence of Pb2+ reduced the Cd2+ removal with N-OP, indicating that the Pb2+ adsorption was preferential. This behavior may contribute to a selective removal of the heavy metal ions from the mixture.