Removal of lead(II) from aqueous solutions by activated carbon developed from surplus sludge

JIANG Zhu-wu(蒋柱武)^{1, 2}, WANG Xue-jiang(王学江)², NING Xue(宁薛)²

(1. State Key Laboratory of Pollution Control and Resources Reuse (Tongji University), Shanghai 200092, China;
2. Faculty of Environmental Science and Engineering Technology, Fujian University of Technology,
Fuzhou 350118, China)

Abstract:Activated carbon (AC) was prepared from surplus sludge using chemical activation method with the assistance of ZnCl₂. The influences of process parameters on the AC’s specific surface area and adsorption capacity for Pb²⁺ were examined to optimize these parameters. The optimal conditions for the preparation of AC were determined to be activation temperature of 500 °C, activation time of 1 h, impregnation ratio of 1:1 (solid-to-liquid volume) with the 30% ZnCl₂ solution (mass fraction), giving the BET surface area of 393.85 m²/g and yield of 30.14% with 33.45% ash. Also, the pyrolysis temperature was found to be the most important parameter in chemical activation. FTIR spectra provided the evidence of some surface structures such as C=C and C—O—C. In the adsorption studies, a rise in solution pH led to a significant increase in adsorption capacity when the pH value varied from 3.0 to 7.0, and the optimal pH for removal of Pb²⁺ was 7.0. It was observed that the pseudo-second-order equation provided better correlation for the adsorption rate than the pseudo-first-order and the Langmuir model fitted better than the Freundlich model for adsorption isotherm. The adsorption capacity of AC to Pb²⁺ was 11.75 mg/L at solution pH 7.0, the equilibrium time 480 min and 25 °C. Moreover, the adsorption process is endothermic according to the value of enthalpy change.

Key words:sludge-based activated carbon; surplus sludge; preparation; Pb²⁺; adsorption