ABSTRACT
The Pb(II) adsorption characteristics of chemically activated waste activated sewage sludge (WAS) were compared to raw WAS. Adsorption kinetics and equilibrium isotherm parameters were fit using classic adsorption models. HCl and H2SO4 activation terminated any significant sludge-based adsorption. Raw and ZnCl2 activated WAS displayed Langmuir adsorption capacities of 307 mg/g and 274 mg/g, respectively. Surface characterization revealed that chemical activation with ZnCl2 increased the BET surface area for raw WAS from 0.97 m2/g to 1.78 m2/g, but did not significantly change the surface structure. FTIR analyzes and XPS were used to further investigate the nature of lead binding. The relationships between equilibrium ion concentration and Pb(II) adsorption suggest cationic exchange with hydrogen, calcium, and zinc as a significant mechanism of Pb(II) removal alongside electrostatic attraction. The pHPZC was determined as 2.58 and 2.30 for ZnCl2 activated WAS and raw WAS respectively. HNO3 and Ca(NO3)2 demonstrated sufficient elution properties for WAS recovery. For authentic industrial effluent both raw and ZnCl2 activated WAS displayed Pb(II) removal behavior comparable to simulated Pb(II) solutions. In comparison with modified and unmodified sludges from literature, this study demonstrates the auspicious potential of raw WAS as an effective Pb(II) adsorbent independent of pyrolytic or chemical activation.