A role for adsorption in lead leachability from MSWI bottom ASH

Owing to its high porosity and large surface area, bottom ash from municipal solid waste incineration (MSWI) has been previously suggested as an adsorbent for removing heavy metals from wastewater. However, since lead leachability is not clearly understood, this study reports the behavior of lead for leaching from MSWI bottom ash, classified as NH, W and H. Leaching kinetics show a sorption/desorption mechanism producing equilibrium in the leachates. Adsorption experiments reveal a similarly high saturation coverage for NH, W and H bottom ash, demonstrating a considerable adsorption capacity. Adsorption mainly reflects an ion exchange mechanism. Successive leaching experiments prove that at least two species of lead can be stripped from bottom ash: one is Pb(OH)42- and the second, identified by XAS, is a lead complex sorbed on the surface of Fe colloïd or FeOOH polymers.