A new strategy to stabilize the heavy metals in carbonized MSWI-fly ash using an acid-resistant oligomeric dithiocarbamate chelator.

Fly ash (FA) derived from municipal solid waste incineration (MSWI) requires safe handling before landfilling due to its extremely high salt content and the risk of leaching heavy metals (HMs) under acidic conditions. Herein, aimed at improving the acid stability of dithiocarbamates, a cost-effective oligomeric dithiocarbamate (ODTC) was developed to stabilize HMs from carbonated MSWI-FA. Spiking of 3.6 wt% ODTC reduced the HM leaching below landfill standards in China, even across the pH range of 2.0–13.0 or 8-week exposure to the natural environment. Stabilization decreased the acid-soluble/exchangeable fractions of Cd, Pb, and Zn from 22.2%, 4.49%, and 21.9% to 0.14%, 0.11%, and 12.2%, respectively, resulting in safe levels for Pb and Cd with risk assessments. Compared to DDTC and SDD, ODTC exhibited higher stability under acidic conditions after chelation with the HMs, minimized the risk of HM leaching, and significantly reduced stabilization costs. In-depth studies proved that the stabilization mechanism involved the ability of ODTC to chelate HMs strongly and form acid-resistant ODTC-HM complexes, agglomeration of the MSWI-FA grains to encapsulate the ODTC-HM complexes, transformations of the HMs from acid-soluble species to stable oxidizable and residual species, and specifically ODTC reducing high-valent Pb to more stable Pb(II) species. [Display omitted] • Acid-resistant ODTC was innovatively synthesized for MSWI-FA stabilization. • Up to 99.8% of Cd and Pb were transformed into stable forms resisting leaching. • ODTC minimized the environmental risks of MSWI-FA even at extreme pHs of 1.0 and 13.5. • Stabilization with ODTC substantially reduced costs outshining other stabilizers. • Mechanistic insight into MSWI-FA stabilization by ODTC was thoroughly conducted. [ABSTRACT FROM AUTHOR]