Pb(II) adsorption behaviour onto raw and chemically activated waste activated sludge

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 with commonly used models. HCl and H2SO4 activation terminated any significant sludge-based adsorption. ZnCl2 activated WAS was found to have an adsorption capacity of approximately 274 mg/g, while raw, unactivated WAS had a capacity of approximately 307 mg/g. 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 surface structure. FTIR analyses 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 behaviour 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.