Abstract
The adsorption characterizations of the biosorbent extracted from waste activated sludge after short-time aerobic digestion were investigated by adsorbing Pb2+ and Zn2+ from aqueous single metal solutions. The adsorption kinetics were well fit for the pseudo-second-order model. Compared with Freundlich and Temkin models, Langmuir model better described the adsorption isotherms. The maximum adsorption capacities of the biosorbent (793.61 mg Pb2+/g and 408.38 mg Zn2+/g) were markedly higher than those of the reported biosorbents. Thermodynamic analyses indicated that the sorption processes were feasible and spontaneous in nature. The surface morphology of the biosorbent showed a meshy structure with small branches, which was ideal for the biosorbent to quickly capture the metal ions. The energy dispersive X-ray spectra confirmed that the adsorbed metal ions lay in the precipitates of the adsorption reactions. Fourier transform infrared analyses showed that the major functional groups are responsible for the adsorption. The adsorption of the biosorbent for Pb2+ and Zn2+ was mainly physisorption in nature enhanced by chemisorption. Complexation and ion exchange between the functional groups and the metal ions played an important role in the chemisorption.
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