Associated Adsorption Characteristics of Pb(II) and Zn(II) by a Novel Biosorbent Extracted from Waste-Activated Sludge

The associated adsorption of Pb2+ and Zn2+ by a novel biosorbent extracted from waste-activated sludge (WAS) after short-time aerobic digestion is systematically investigated by using aqueous binary metal solutions. Zn2+ slightly inhibited Pb2+ adsorption onto the biosorbent, while Pb2+ markedly inhibited Zn2+ adsorption onto the biosorbent. When the total mass concentrations of metal ions in the disposed solutions were the same, the total adsorption capacity of the biosorbent for Pb2+ and Zn2+ in the binary-metal solution was more than that for Pb2+ in a single-metal solution, but less than that for Zn2+ in a single-metal solution. Moreover, a rising proportion of Zn2+ concentration in the binary-metal solution was found to increase the total adsorption capacity of the biosorbent. Both the Langmuir model and Freundlich model commendably described the adsorption isotherms of Pb2+ and Zn2+ in the associated adsorption system. The maximal adsorption capacity for each metal ion in the binary-metal solution was obviously clearly lower than that in the single-metal solution. The spectra of energy dispersive X-ray confirmed that the adsorbed metal ions lay in the precipitates of the adsorption reactions. The spectra of Fourier transform infrared spectroscopy revealed that complexation and ion exchange between the functional groups and the metal ions played an important role in the associated adsorption process.