CO2 mineralization of bottom ash and decarbonation of waste-to-energy plants

Following the Paris agreements on climate change, CO₂ emissions from large emitters have become the focus of particular attention. With a national average of 0.4 kg of fossil CO₂ emitted per kg of Municipal Solid Waste (MSW) incinerated, bottom ash (BA) residues from waste-to-energy (WtE) plants in France are possible candidates for CO₂ mitigation by mineralization, considering BA as feedstock for CO₂ capture and production of alternative construction materials.

BA samples collected from an operating WtE plant in the suburb of Lyon were carbonated under slurry or humidity-controlled conditions. It was found that 35 kg of CO₂ could be captured per tonne of minus 100 μm ground BA in 30–120 min at ambient conditions. A water pre-washing stage was necessary to prevent the production of H₂ by oxidation of Al metal during carbonation and removed chlorides and sulfates that are undesirable in construction materials.

While it is argued that CO₂ mineralization is of limited interest for mitigating the CO₂ emissions of WtE facilities, a conservative analysis of a production system that associates a WtE plant and a cement plant reveals that the net carbon footprint of such a combined production system could be reduced by 15 % with an added mineralization process.