Removal of lead from aqueous solutions by ferric activated sludge-based adsorbent derived from biological sludge

Ferric activation was novelly used to prepare sludge-based adsorbent (SBA) through pyrolysis treatment of biological sludge, and the adsorbents were applied to adsorb Pb2+ ions from aqueous solution. The ferric-activated SBA showed a favorable porous structure development and enhanced Pb2+ ions removal, with the maximum sorption capacity of 42.96mg/g. The optimum adsorption was observed in a wide pH range of 4–6. The adsorption data fitted the Freundlich model well, indicating heterogeneous lead coverage on the adsorbents. Pseudo-second order model validated the kinetic data, suggesting that the rate-limiting step of the adsorption process was chemical sorption. The mechanism of Pb2+ ions removal involved ion exchange, precipitation, and surface complexation. The higher adsorption of ferric-activated SBA was due to the enhancive surface area that provided a larger number of active sites for adsorbate, the precipitation, and the formation of the surface complex FeOPb2+. The results demonstrate that ferric-activated SBA can be used as an effective adsorbent for Pb2+ ions removal from aqueous solution, which will also provide an option for sludge valorization.