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

The associated adsorption of ${\mathrm{Pb}}^{2+}$ and ${\mathrm{Zn}}^{2+}$ by a novel biosorbent extracted from waste-activated sludge (WAS) after short-time aerobic digestion is systematically investigated by using aqueous binary metal solutions. ${\mathrm{Zn}}^{2+}$ slightly inhibited ${\mathrm{Pb}}^{2+}$ adsorption onto the biosorbent, while ${\mathrm{Pb}}^{2+}$ markedly inhibited ${\mathrm{Zn}}^{2+}$ 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 ${\mathrm{Pb}}^{2+}$ and ${\mathrm{Zn}}^{2+}$ in the binary-metal solution was more than that for ${\mathrm{Pb}}^{2+}$ in a single-metal solution, but less than that for ${\mathrm{Zn}}^{2+}$ in a single-metal solution. Moreover, a rising proportion of ${\mathrm{Zn}}^{2+}$ 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 ${\mathrm{Pb}}^{2+}$ and ${\mathrm{Zn}}^{2+}$ 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.