Methodology for Evaluating the CO₂ Sequestration Capacity of Waste Ashes

The concentration of CO₂ in the atmosphere is constantly increasing, leading to an increase in the average global temperature and, thus, affecting climate change. Hence, various initiatives have been proposed to mitigate this process, among which CO₂ sequestration is a technically simple and efficient approach. The spontaneous carbonation of ashes with atmospheric CO₂ is very slow, and this is why accelerated carbonation is encouraged. However, not all ashes are equally suitable for this process, so a methodology to evaluate their potential should be developed. Such a methodology involves a combination of techniques, from theoretical calculations to XRF, XRD, DTA-TG, and the calcimetric determination of the CaCO₃ content. The present study followed the approach of exposing ashes to accelerated carbonation conditions (4% v/v CO₂, 50-55% and 80-85% RH, 20 °C) in a closed carbonation chamber for different periods of time until the maximum CO₂ uptake is reached. The amount of sequestered CO₂ was quantified by thermogravimetry. The results show that the highest CO₂ sequestration capacity (33.8%) and carbonation efficiency (67.9%) were obtained for wood biomass bottom ash. This method was applied to eight combustion ashes and could serve to evaluate other ashes or comparable carbon storage materials.