Application of accelerated carbonation on MSW combustion APC ash for metal immobilization and CO2 sequestration

The present study focuses on the application of an aqueous phase accelerated carbonation treatment on air pollution control (APC) residues from municipal solid waste combustion, aimed at assessing its influence on the environmental behaviour of the residue under concern, as well as the potential of the process in terms of sequestration of the CO2. APC residues are considered hazardous waste and must be treated before final disposal in order to achieve the immobilization/mobilization of critical contaminants such as heavy metals as well as mobilization of soluble salts. The treatment applied proved to be effective in reducing the mobility of Pb, Zn, Cr, Cu and Mo, the optimum final pH for the carbonated APC residues being in a range of 10–10.5, whilst a mobilization effect was noticed for Sb and no effect was assessed for chlorides. The effect of carbonation treatment on the contaminant release was further evaluated by means of a sequential extraction procedure, indicating that the distribution of contaminants on water soluble, exchangeable and carbonate fraction was modified after treatment. The CO2 sequestration potential assessed for the APC residues showed that the carbonation technology could be a technically viable option in order to reduce emissions from WtE plants.