The effects of accelerated carbonation on CO2 uptake and metal release from incineration APC residues

This work presents the results of a study on acceleratedcarbonationof incinerator air pollution control residues, with a particular focus on the modifications in the leaching behaviour ofthe ash. Aqueous carbonation experiments were carried out using 100% CO2 at different temperatures, pressures and liquid-to-solid ratios, in order to assess their influence on process kinetics, CO2 uptake and the leaching behaviour of major and trace elements. The ash showed a particularly high reactivity towards CO2, owing to theabundance of calcium hydroxides phases, with a maximum CO2 uptake of ∼250 g/kg. The main effectsofcarbonation on trace metal leaching involved a significant decrease in mobility for Pb, Zn and Cu at high pH values, a slight change or mobilization for Cr and Sb, and no major effects on the release of As and soluble salts. Geochemical modelling of leachates indicated solubility control by different minerals after carbonation. In particular, in the stability pH range of carbonates, solubility control by a number ofmetal carbonates was clearly suggested by modelling results. These findings indicate that acceleratedcarbonationof incinerator ashes has the potential to convert trace contaminants into sparingly soluble carbonate forms, with an overall positive effect on their leaching behaviour. Article Outline