Carbon reclamation from biogas plant flue gas for immobilizing lead and neutralizing alkalis in municipal solid waste incineration fly ash

• Flue gas was utilized towards MSWI-FA for immobilizing Pb and neutralizing alkalis. • A maximum 95.66% of Pb leaching toxicity was reduced after 4.5 h carbonation. • A standardized leaching pH of 8.80 was realized after 4.5 h carbonation. • The co-treatment was mainly attributed to the protection from CaCO 3 boundary layer. • The reduction of carbon emission and operation cost were achieved in this study. Immobilizing heavy metal lead (Pb) and controlling alkalinity are crucial for municipal solid waste incineration fly ash (MSWI-FA) while carbon emission from incineration flue gas has hardly peaked yet. In this study, an actual flue gas from biogas plant was used for stabilizing Pb and neutralizing alkalis in MSWI-FA. Results indicated that carbonation process further incremented the Pb immobilization rate by 58.99%–95.66% based on agent treatment. With increasing carbonation time to 4.5 h, the unstable exchangeable fraction tended to zero, contributing to a leaching decrease of Pb correlated with pH, except in a strongly acidic environment. The formation of calcium carbonate boundary layer made Pb leachability less susceptible to the influence from curing time, while reduced the leaching pH to standard-satisfied 8.80. After the carbonation, 0.13 g CO2 /g MSWI-FA was calculated as the theoretical carbon dioxide (CO 2 ) capture capacity, with a cost reduction of 5.5% compared to direct agent treatment. All the results demonstrated that the flue gas carbonation combined with agent stabilization was a promising choice for MSWI-FA treatment due to the upgrade of economy and downgrade of carbon emission.