Experimental Study of Mineral Carbonation of High-Calcium Fly Ash: CO₂ Sequestration and Its Effect on Pozzolanic Reactivity

Mineral carbonation of industrial wastes offers a sustainable approach to carbon sequestration and waste valorization. This study investigates the aqueous mineral carbonation of three high-calcium fly ashes under ambient conditions using recyclable sodium carbonate solutions. The effects of operational parameters, including liquid-to-solid ratio (L/S), sodium carbonate concentration, and carbonation duration, were systematically analyzed using response surface modeling. A degree of carbonation (DOC) up to 52% was achieved within one hour under ambient conditions, with calcite (CaCO3) identified as the dominant product phase. Advanced characterization techniques revealed significant transformations in the physicochemical properties of carbonated fly ashes (CFAs), including increased particle size and reduced density. Notably, the carbonation process induced a linear decrease in pozzolanic reactivity, with a reduction in cumulative heat release from 19.2 J/g to 15.8 J/g per gram of CO2 sequestered. Despite the reduction, CFA with 9.5 wt% CO2 sequestered meets RILEM criteria for pozzolanic reactivity, demonstrating its potential as a sustainable component in low-carbon concrete systems.