High capacity Pb(II) adsorption characteristics onto raw- and chemically activated waste activated sludge.

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 HSO activation terminated any significant sludge-based adsorption. Raw and ZnCl activated WAS displayed Langmuir adsorption capacities of 307 mg/g and 274 mg/g, respectively. Surface characterization revealed that chemical activation with ZnCl increased the BET surface area for raw WAS from 0.97 m/g to 1.78 m/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 pH was determined as 2.58 and 2.30 for ZnCl activated WAS and raw WAS respectively. HNO and Ca(NO) demonstrated sufficient elution properties for WAS recovery. For authentic industrial effluent both raw and ZnCl 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.