Mechanistic insight into mineral carbonation and utilization in cement-based materials at solid-liquid interfaces

In order to ensure the viability of CO₂ mineralization and utilization using alkaline solid waste, a mechanistic understanding of reactions at mineral-water interfaces was required to control the reaction pathways and kinetics. In this study, we provided new information for understanding the reactions of CO₂ mineralization and utilization at mineral-water interfaces. Here we have carried out high-energy synchrotron X-ray analyses to characterize the changes of mineral phases in petroleum coke fly ash during CO₂ mineralization and their subsequent utilization as supplementary cementitious materials in cement mortars. The 2-D synchrotron patterns were converted to 1-D diffraction patterns and the results were then interpreted via the Rietveld refinement. The results indicated that there was a continuous source of calcium ions mainly due to the dissolution of CaO and Ca(OH)₂ in fly ash. This would actually enhance the driving force of saturation index at the solid-fluid interfacial layer, and then could eventually result in the nucleation and growth of calcium carbonate (calcite) at the interface. A small quantity of CaSO₄ (anhydrite) in fly ash was also dissolved and simultaneously converted into calcite. In addition, the calcium sulfate in fly ash would effectively prevent the early hydration of tricalcium aluminate in blended cement, and thus could avoid the negative impact on its strength development. The proposed reaction mechanisms were also qualitatively verified by X-ray fluorescence mapping and electron microscopy. These results would help to design efficient reactors and cost-effective processes for CO₂ mineralization and utilization in the future.