Modification of Desulfurization Ash via Thermal CO₂ Treatment: Oxidation Behavior, Carbonation Characteristics, and...

Desulfurization ash (DA) is a kind of industrial solid waste generated during flue gas desulfurization. To overcome the limited utilization of reactive calcium-bearing constituents and the insufficient mineralogical stability of DA, this study proposes a thermal CO₂ modification approach based on the synergistic coupling of oxidation and carbonation, and systematically investigates the associated evolution of mineral phases and microstructural features. The effects of reaction temperature, CO₂ flow rate, and reaction time are evaluated using TG-DSC, XRD, FT-IR, SEM-EDS, particle size analysis, and carbon-sulfur analysis to elucidate the reaction behavior of DA under a CO₂ atmosphere. The results demonstrate that reaction temperature is the dominant factor governing the modification process. During heating, CaSO₃ is preferentially oxidized to CaSO₄ under the CO₂ atmosphere, thereby stabilizing the sulfur-bearing components. Subsequently, Ca(OH)₂ undergoes carbonation to form CaCO₃, simultaneously contributing to CO₂ sequestration. Under the optimized conditions of 450 °C, a CO₂ flow rate of 120 mL/min, and a reaction time of 60 min, the resulting CaCO₃ exhibits a pronounced needle-like CaCO₃ morphology, while the CO₂ uptake reaches a maximum of 16.71%. These findings clarify the coupled oxidation-carbonation mechanism and mineral transformation behavior of DA during thermal CO₂ modification, providing a theoretical basis and technical reference for the low-carbon utilization of industrial solid wastes.