The Influence of Liquid/Solid Ratio and Pressure on the Natural and Accelerated Carbonation of Alkaline Wastes

The purpose of this research is to assess the yield and reaction rate potential of carbon dioxide (CO2) sequestration through mineralisation using readily available and inexpensive resources by exploiting waste materials. In this case, a blend of four different kinds of ashes and combustion by-products were used, namely, coal fly ash (CFA), flue gas desulphurization (FGD) residues, municipal solid waste incineration fly ashes (MSWI FA) and bottom ash (MSWI BA), produced at the same location. To highlight the impact of these materials on the carbonation process, various factors were analysed, including particle size distribution, immediately soluble contents, mineralogy, particles’ detailed structure, and chemical composition. After preparing the samples, two carbonation processes were tested: natural carbonation and accelerated carbonation. To evaluate the impact of the water content on the reaction rate and yield of the mineral carbonation, various liquid-to-solid (L/S) ratios were used. The results demonstrate that the water content and pressure play a significant role in the CO2 sequestration during the accelerated carbonation, the higher the L/S, the greater the yields, which can reach up to 152 g CO2/kg with MSWI FA, while no substantial difference seems to emerge in the case of the natural carbonation.