Flow-through carbonation of waste incinerator bottom ash in a rotating drum batch reactor: Role of specific CO2 supply, mixing tools and fill level

Abstract Bottom ashes (BA) constitute the dominant solid residue of municipal solid waste incineration. Ageing of BA over a period of several months is known to reduce the reactivity and leachability of critical trace metals via carbonation by atmospheric CO 2 . This process may be accelerated by contacting the material with CO 2 -rich exhaust gas in rotating drum reactors. In this study, we investigated carbonation of BA under dynamic conditions with continuous feed of the reactant gas. This is of particular interest for the integration of the process with the management of BA at incinerator sites. The effects of specific CO 2 supply, mixing tools, and reactor loadings on process performance were assessed by the leaching behaviour of the treated BA. The experiments were performed in a rotating drum. Overall, carbonation improved the leachate quality of BA. Leachate values characterized the reactor output as a non-hazardous waste when the specific CO 2 supply was above 100 g CO 2 per kg BA. The reaction could be accelerated to around 100 min and was enhanced by the use of mixing tools. Of the configurations tested, a perforated mixing cage performed best even at fill levels of up to 50%. This set-up was also least prone to the formation of BA incrustations.