CO2 sequestration by direct gas-solid carbonation of air pollution control (APC) residues

Direct gas-solid carbonation of alkaline residues from air pollution control (APC) systems was investigated with the aim of evaluating its contribution as a CO2 storage option as well as its effect on the properties of the residues, namely, the leaching behavior, which may affect the strategies for their disposal or reuse. APC residues from a medical solid-waste incinerator located in the vicinity of Rome, Italy, were selected for performing carbonation experiments with pure CO2 at reaction temperatures in the 200-500 degrees C range. The extent of calcium conversion to the carbonate form was found to be negligible below 300 C, whereas the maximum conversion of 57% was already measured at 400 degrees C. This implies a storage capacity of 0.12 kg of CO2/kg of dry solid. Considering that the APC residues production in the EU25 equals 1260 kiloton/year, this translates in a CO2 storage potential for the European market of 0.15 megatons of CO2/year. On the basis of the ENV 12457-2 leaching test procedure performed after accelerated carbonation, the concentrations of Cd, Cu, and Cr in the leachate were below the limits imposed by the Italian regulation for disposal in nonhazardous waste landfills, whereas only the lead concentration still exceeded the corresponding limit value. These results indicate that accelerated carbonation of alkaline residues could be suitable to address the issue of CO2 storage, especially for niche applications such as at steel plants and solid-waste incinerators, where both the residues and the CO2 are present.